Implementing a Biointensive Strategy for Caterpillar Control in Sweet Corn

Final Report for LNE99-118

Project Type: Research and Education
Funds awarded in 1999: $68,265.00
Projected End Date: 12/31/2003
Matching Non-Federal Funds: $19,102.00
Region: Northeast
State: Massachusetts
Project Leader:
Ruth Hazzarad
University of Massachusetts
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Project Information

Summary:

One-third of the vegetable acreage in the Northeast is devoted to sweet corn, and it plays a vital role in direct retail sales as an anchor crop that attracts customers into markets. Insecticide use remains high in sweet corn despite widespread implementation of IPM, primarily because of two caterpillar pests, corn earworm (Helicoverpa zea, Boddie) (CEW) and European corn borer (Ostrinia nubilalis, J. E. Smith) (ECB). Left uncontrolled, these caterpillars render sweet corn unmarketable as a result of feeding damage and frass in the ears. Ecologically sustainable methods for weed, soil and nutrient management have been developed, but corn earworm, in particular, remains a critical barrier for farmers who seek to produce marketable corn without broad-spectrum insecticides. Through previous SARE-funded projects we have developed an integrated bio-intensive strategy for caterpillar control using vegetable oil and Bacillus thuringiensis.

The bio-intensive caterpillar control strategy consists of IPM methods of monitoring for moths and scouting insect damage in corn, foliar sprays of Bt to control ECB and the fall armyworm (FAW) when present, and a single application of vegetable oil with added Bt to the silk for CEW control. At the outset of the project this bio-intensive system was sufficiently developed to test it on vegetable farms throughout the New England region. A hand-held pump applicator, called the ‘Zea-later’® had been designed and patented at the University of Massachusetts and Hampshire College, was in the process of being commercialized, and could provide an economically viable means of applying the treatment.

In this project, the efficacy of this integrated bio-intensive strategy was evaluated on eight cooperating farms throughout New England. On these same cooperating farms a qualitative assessment of the impact of using this caterpillar control strategy on production and marketing of sweet corn and other crops was conducted through a series of interviews.
Significant reductions in the amount of caterpillar damage were achieved on all farms. Six of the eight growers are continuing to grow corn and all of those will continue to use the bio-intensive control strategy and techniques after the completion of the project.

Further experiments were conducted to determine the optimal timing and longevity of oil and Bt treatments for highest ear quality and greatest corn earworm control, by examining how direct silk applications of oil influence the developing ear kernels and larval mortality. Oil treatments were shown to interfere with silk pollination and kernel development; treatments applied before day 3 resulted in severe underdevelopment and unmarketable corn ears. The best time to treat the ears for greatest caterpillar control and the least amount of undeveloped kernels is between days 5 and 7 after first silk appearance.

Introduction:

OBJECTIVE 1

Eight diversified vegetable farmers in five New England states, hoping the bio-intensive system could open the door to season-long organic production of clean corn, tested the method through on-farm experiments over three years. The first year of trials, 1999, was funded by a separate grant from the Organic Farming Research Foundation and followed very similar protocols; hence, results from all three years will be reported here. Each winter during project years (2000, 2001, and 2002) growers and researchers met for a day long meeting to review the previous season’s results, discuss improvements, and plan for the coming season.

The bio-intensive system was subjected to a wide variety of field conditions and pest pressures on the participating farms. Two of the farms are located on the New England coast in the direct migratory path of the corn earworm and receive regular visits from large numbers of CEW each summer. Another four farms are within 120 miles of the coast and usually have significant numbers of CEW by the end of the summer. Two farms are further up the Connecticut River Valley in southern Vermont, within 3 hours of the southern coast of New England, and usually get CEW, but are sometimes spared. The farms represent a wide diversity of size, management styles, and markets for their vegetables, including wholesale, farmers’ market, farmstand, and Community Supported Agriculture (CSA).

OBJECTIVE 2

The impact of the bio-intensive caterpillar control strategy on the whole-farm system could be significant, and unique, at each of the participating farms. These eight farms have different kinds of markets, including farmstands (4 farms), farmers markets (3 farms), Community Supported Agriculture (CSA) (2 farms), and wholesale (1 sells exclusively wholesale, 2 others partially). They grow from 7 to 36 acres of vegetables, farm in 5 states, and are in coastal, river valley or interior locations. A successful corn earworm strategy will open the door to marketing clean organic corn on five of the farms, will bring the option of organic instead of IPM corn (and whole-farm organic certification) to one farm, and will make it feasible to grow corn for the first time on two of the farms.

OBJECTIVE 3

The three experiments in Objective 3 were designed to develop a better understanding of how direct silk applications of oil influence the developing ear kernels, especially at the tip, and larval mortality, in order to determine the optimal timing of oil treatments for highest ear quality. Experiment 1 looks at the effect of the day of oil application on the final ear quality at harvest. Experiment 2 examines the longevity of the oil treatment over time, and Experiment 3 looks more closely at the timing of pollination of the silks and subsequent development of the ear.

EXPERIMENT 1

Oil applications can result in slightly reduced tip fill and ear length. This effect, called cone-tip or tip stunting, has been identified in previous studies (Carruth, 1942; Siedlecki et. al., 1996). In one study, canola oil reduced total ear length by an average of 1.8 cm and the proportion of the ear with fully developed kernels by 6% (Hazzard and Gault, 1993). This effect occurs with both mineral and vegetable oil and is only slightly influenced by oil dose (Hazzard et. al., 1997). Previous studies suggested that it can be reduced, though not eliminated, by waiting until at least 4 days after visible silk initiation to apply oil; however, waiting more than 6 days after silk initiation may allow higher levels of feeding damage to occur (Carruth, 1941; Siedlecki, 1996; Hazzard, 1997).

The objective of this experiment was to determine the optimal timing of oil treatments by exploring the relationship of the timing of oil application to the development of ear kernels, especially in the tip, as well as to larval mortality and feeding damage to kernels.

EXPERIMENT 2

Migrating flights of corn earworm reach Massachusetts in late July and may continue through August and September. The number of moths varies considerably from year to year and week to week, which may result in continuous or fluctuating activity throughout the silking period of any given planting of corn. While corn earworm moths prefer to deposit eggs on fresh silks, they may lay eggs on silks throughout the three-week silking period. Depending on the temperature, eggs hatch in 3 to 7 days, thus, larvae could enter the silk channel any time from a few days after first silk to harvest. Since the oil is only applied once during the silking stage, it is critical to know how long the oil applications will protect the ears. The objective of this experiment was to compare oil and Bt, alone and in combination, to determine their effectiveness against the CEW over time.

EXPERIMENT 3

Development of the silks begins at the base of the cob and proceeds up the tip (Duncan, 1975). It appears that oil may cause cone-tip through interference with pollination. The tip silks are still growing towards the husk opening long after the silks from base of the ear have emerged from the husk and been fertilized, thus the bottom kernels are pollinated first. If silks become covered with oil at this point, the oil may prevent pollination and subsequent fertilization of the kernels at the tip. An additional experiment was conducted to study kernel growth over time and how this was affected by oil or other interruptions of pollination.

Project Objectives:
  1. 1) Evaluate the efficacy and cost of an integrated bio-intensive strategy using Bacillus thuringiensis and vegetable oil for control of key caterpillar pests of fresh market sweet corn on eight cooperating farms.

    2) On the same cooperating farms, conduct a qualitative assessment of the impact of using the caterpillar control strategy on production and marketing of sweet corn and other crops.

    3)a. Develop a better understanding of how direct silk applications of oil influence the developing ear kernels in order to determine the optimal timing of oil treatments for highest ear quality.
    b. Determine the timing (day) of the oil application to achieve the best corn earworm control.
    c. Evaluate the effect of corn oil based insecticide on sweet corn ear development.

Cooperators

Click linked name(s) to expand
  • Anne Carter
  • Andy Caruso
  • Doug Coldwell
  • Rosalind Cook
  • Tom Harlow
  • Rob Johanson
  • Dan Kaplan
  • Jack Manix
  • Steve Mong
  • Skip Paul
  • Eric Sideman
  • Pamela Westgate

Research

Materials and methods:
OBJECTIVE 1

Eight diverse farms throughout New England participated in this 3-year study. Five participating farms are certified organic, one is in transition from conventional to organic, and two use mostly organic techniques but are not certified. See Objective 2 for more detailed farm profiles.

Planting & experimental design: On each of eight farms 3 blocks of corn of the same variety were planted at least 7 days apart after May 30 in 1999 and 2000, and after May 24 in 2001. Blocks were planted in succession so that they would be subject to a range of pest conditions during the latter part of each season when corn earworm pressure is the highest, in August and September. In 2000 and 2001 the Delectable variety (82DH, bicolor SE+) was selected by the growers and planted in all experimental blocks (Crookham Seed Co, Caldwell, Idaho). Each planting was at least 8 rows wide by 200′ long, and split into two blocks that measured 8 rows x 50-75′. In this split-block design one block was not treated with oil. In the other block the top ear on each plant was treated, by the grower or a farm employee, with 0.5 ml of emulsified corn oil mixed with Bacillus thuringiensis, subs. kurstaki. When foliar sprays of Bt were applied, they were applied to all of the corn (treated and untreated) in a planting. One of the eight participating growers planted only one block of corn in 2000 (early May) and did not participate in 2001 (see case studies, Objective 2). The seven other farms participated for all three years and harvested 1 to 3 blocks per year.

Each grower was provided with a Zea-later® oil applicator (prototypes in 1999 and 2000, market version in 2001). They were also provided with mixing instructions, measuring devises, corn oil (Stop & Shop brand), Bt and Nufilm 17 (Miller Chemical & Fertilizer Corp., Hanover, PA) as a spreader-sticker for the foliar sprays. In 1999 the growers were provided with corn oil and the Bt formulation, Condor WP wettable powder (Ecogen Inc., Langhorne, PA); however, a dry Bt product when mixed directly in oil does not achieve a stable suspension and the Bt particles remained large and clogged the applicator. In 2000 and 2001, this problem was solved by providing the growers with corn oil containing 10% emulsifier (Cirrasol 1087, Uniquema, New Castle, DE), and by dissolving the Bt dry flowable (Dipel DF, Valent Agricultural Products, Richardson, Texas) in water prior to mixing with oil. This produces an even suspension of fine particles. The growers mixed batches of the oil/ Bt suspension the day of use at a rate that gives the equivalent of approximately 0.5 lb/acre (for Dipel DF: 3 Tbls + 1 tsp granules in 100 ml water per 900 ml emulsified oil) in a stand of corn at 16,000 ears/acre.

Monitoring: On each farm the flights of the corn earworm, European corn borer and fall armyworm were monitored. The fall armyworm traps were located in the youngest corn and were moved between blocks accordingly until they reached the third planting. Here they remained until the corn matured and was harvested. Two Heliothis traps, one with a lure for the Iowa (Z) and one for the N.Y. (E) strains of European corn borer (ECB-1 & ECB-2, Trécé Inc., Salinas, CA), were located at the field edges in weeds or grass throughout the growing season and were removed at the final harvest. Each farm also had two Heliothis traps, each with one corn earworm lure (Hercon 700310, Hercon Environmental Corp., Emigsville, PA). These were placed in each planting as it entered fresh silk and left there for 2-3 weeks during ear development. In 1999 and 2000 foliar Bt sprays were applied only when the European corn borer pest reached threshold numbers as determined by IPM scouting methods. Specifically, we recommended spraying 1.5 lb / acre of Dipel DF, using NuFilm 17 (8 oz./acre) as the spreader-sticker, when >15% of the corn plants had one or more ECB caterpillars or fresh ECB caterpillar damage. The corn was scouted starting at late whorl/pre-tassel stage through early silk by checking 50-100 plants in groups of ten scattered throughout the field. In each group every other plant was examined for caterpillars or signs of fresh feeding until a count of ten plants. When the plants were at pre-tassel stage, the tassels were removed and checked, while in the older corn evidence of ECB was found by examining the stalks, particularly between the stalks and the growing ears.

Foliar Sprays: Because of variability in ECB infestation, not all blocks were sprayed with Bt. In the 2000 season all of the blocks on Walker, Kestrel, Coolwater, and Wishing Stone Farms exceeded the threshold and were sprayed with foliar applications of Bt for ECB. No blocks were treated on Brookfield, Goranson, or The Upper Forty farm and one was treated on Applefield Farm. In some cases these growers chose not to spray even though thresholds were exceeded, either because they lacked spray equipment or because they preferred not to spray. In 2000 fish emulsion was used for a spreader-sticker at Walker and Kestrel Farms instead of NuFilm, and Dipel ES was used to spray all three of the blocks at Walker Farm. In order to achieve consistency in this component of insect management across all blocks the growers were asked in 2001 to apply two foliar Bt sprays of Dipel DF and NuFilm to all of their corn (control and treatment blocks, both), once during green tassel and once during early silk.

Harvest & Scoring: At harvest the top corn ears from untreated and treated corn plants (100 each), of similar stage and appearance, were picked out of the inner six rows at least 5′ from the ends in each block. Each ear was then scored for number, size and type of caterpillars, position of damage relative to the tip and side, and husk damage. Husk damage was scored as present or absent. Caterpillar sizes were scored as follows: first and second instars were grouped together as smalls, while third, fourth and fifth instars were scored separately. Tip or side damage ratings were given depending upon the entry site of the caterpillar: if the caterpillar obviously entered the ear through the side the damage was recorded as side damage, whereas, if the entry was through the side but above the level of the ear tip, or if an entry hole was not visible (ie, the caterpillar came down the silk channel), then the damage was scored as tip damage. Damage was scored as follows: 0=no damage, 1= silk damage only, 2 = damage within top 2” of ear, 3 = damage within top 3”, and 4 = below 3”. After scoring, the corn was returned to the growers for distribution or sale.

The amount of clean corn was determined for each treatment in each block (each planting of corn per farm) for all three years. The number of clean (marketable) ears was defined as the number of ears that had no damage to the ear kernels. Ears that had damage to the silk but no damage to the kernels were considered clean. In practice this definition was more restrictive than a grower would actually need to use because ears that had minor kernel damage and no caterpillar, or a very small caterpillar, were counted as not marketable when they could actually have been sold under most fresh market conditions.

OBJECTIVE 2

The diversity of these farms makes it difficult to conduct a statistically valid systems study of the impact of this new technology. Furthermore, the record-keeping requirements needed to quantify the economic impacts would be very burdensome for growers. Qualitative assessments were therefore conducted to determine the impacts of this method on the farms. We gathered information about each farm and how the bio-intensive caterpillar control in sweet corn affected their operations in four surveys throughout the project and through farm visits and conversations with the farmers during the growing seasons. Initial interviews at the beginning of the project were followed up with a winter survey and grower meeting each year. We used these interviews to get feedback about how the project was going, what questions the growers still had, the design of the Zea-later, and to report the results to date from the experiment. In this section we will describe each of the farms and how corn and the bio-intensive method for caterpillar pests fit into their operation.

OBJECTIVE 3: Experiment 1

Four field studies were conducted, two in 2000 and two in 2001, to measure the effectiveness of corn oil mixed with Bacillus thuringiensis Berliner, subs. kurtaki (Bt) when applied as a direct silk application on 9 different days. Studies were conducted late in the growing season (maturing in late August and September), so that plots would be subject to infestations by migratory flights of corn earworm as well as the second generation of European corn borer . Corn oil + Bt (0.5 mL) were applied directly to the silk channel of the ears using a Zea-later® on silk days 3-11. One treatment did not receive any oil/Bt application.

Planting and experimental design. The sweet corn variety “Delectable” (The Crookham Company, Caldwell, Idaho) was chosen for the study because it is widely used by fresh market sweet corn growers and it was known to be susceptible to cone-tip. “Delectable” is a mid-main season bicolor sugar-enhanced corn. Trials were established at the University of Massachusetts Agronomy Farm in South Deerfield, Massachusetts.
Corn was grown under conventional sweet corn production practices (NE Vegetable Management Guide, 2002-03) in an Occum fine sandy loam variant. In each year (2000 and 2001), two planting were made (designated ‘early’ and ‘late’), planted two weeks apart in 2000 and three weeks apart in year 2001 to achieve varying levels of infestation from migrating populations of corn earworm and the second generation of European corn borer during the silking period.

The planting dates were 9 June (early) and 23 June (late) 2000. Early and late planting dates in 2001 were 5 June and 28 June, respectively.
For each planting, blocks were planted in rows 300 ft long and six rows wide on 5 ft centers. Seeds were planted at a rate of 5 seeds per cm using a six-row seeder. The two outer rows in each block served as guard rows, and all first ears on the stalk in the four inner rows were treated. Within each block 10 plots (30ft) were randomly assigned, representing nine treatment days and one untreated plot. The treatment days were 3, 4, 5, 6, 7, 8, 9, 10, and 11 days from first silk. There were four replications of each block.

First silk, or silk day 1, was defined as the day when 50% or more of the ears show 2.5 cm or more of silk protruding (Adams and Clark, 1995). Day 1 for the early and late plantings in 2000 was 3 August and 17 August, respectively (14 days apart). August 5 and 27 August (22 days apart) were designated as day 1 for the early and late planting in 2001. In each planting, any corn stalks with a first ear that was behind or beyond this day 1 stage were cut down, and the remaining plants were assumed to be developmentally uniform.
Monitoring and Foliar Sprays. Moth flights and caterpillar infestations were monitored using the same protocols as in the grower trials (Objective 1). Pre-silk foliar applications were purposely not applied in 2000 to assess the total level of damage that could be caused by both corn earworm and European corn borer. In 2001, in order to reduce the confounding effects of side damage to ears, plots were scouted prior to silking and foliar sprays were applied based on standard IPM thresholds for infestation with fall armyworm (Pseudaletia unipuncta, Haworth) or European corn borer. An unusual area-wide invasion of fall armyworm in whorl-stage stage corn was controlled on 6 July 2001 with Spintor 2SC (spinosad, Dow AgroSciences, Indianapolis, Ind.) at a rate of 133 ml·ha-1. In the late planting of 2001 Dipelâ DF (Bacillus thuringiensis kurstaki, Valent BioSciences Corp., Richardson, TX) at a rate of 1.9 lb/acre with a sticking agent (Nufilm-17, Miller Chemical & Fertilizer, Hanover, PA) added at the rate of 0.16 gal/acre was used as a foliar spray against European corn borer on 23 August 2001, prior to silking.

Oil Treatments. The oil + emulsifier + Bt treatment materials and preparation were identical to the oil preparation described in the grower trials (Objective 1). All liquids were agitated manually and regularly during application to keep materials in suspension. The treatments were applied at 1030 HR starting 3 days after first silk and on silk days 4, 5, 6, 7, 8, 9, 10, and 11.

Harvest, larval and damage assessment. Ears were harvested at maturity, on silk day 25, for both plantings in both years. At the time of harvest, ears were at milk stage and suitable for direct market sale. In 2000, this was 28 August (early) and 11 September (late). In 2001, harvest took place on 28 August 2001 (early), and 15 September 2001 (late). Twenty-five ears were selected randomly within each plot, placed in bags, and stored in a 3.3 °C cooler overnight. The next day, the number of corn earworm and European corn borer found on each ear were recorded and the location and level of the damage was assessed as in Objective 1. Any presence of feeding injury or frass was assessed as damage. The husk was considered damaged if an entry hole was found in the husk. Total ear and cone-tip length (length of undeveloped kernels) was measured. Cone-tip was expressed as a percent of total ear length (length of cone-tip divided by the total length of the ear, expressed as a percentage).

Design and statistics. Due to differences in environmental and physical conditions in 2000 and 2001, the data for each year was analyzed separately. The experimental design was a randomized complete block within each planting date and each year, with four replications. The data from 25 ears in each plot and 4 replications (total of 100 ears per treatment day) were analyzed using the general linear model (GLM) of SAS (SAS v.8.2 for Windows, SAS Institute, Cary, NC) to evaluate significance of treatment dates on number of corn earworm, the number of European corn borer, and the type and location of damage on the ears. Linear regression was used to evaluate the relationship between the location of damage or number of larvae and treatment day. Regression was also used to determine the relationship between percent cone-tip and treatment day. The comparison between the treatments and the control was done using a two-tailed Dunnett’s test at P< 0.05 (Dunnett, 1955).

OBJECTIVE 3: Experiment 2

Field studies were conducted in 2000 and 2001 to rate the efficacy and longevity of four pesticide treatments against corn earworm larvae (CEW) in sweet corn. The four treatments used were 1) corn oil, 2) Bacillus thuringiensis, Berliner, subs. kurstaki [(Bt) Dipel DFÒ], 3) oil + Bt, and an 4) untreated plot. All treatments were applied on silk day 5. Silk day 1 was the first day that more than 50% of the ears had 2.5 cm (1 in.) or more of silks emerging using a hand-held pump applicator. Two first-instar CEW larvae were placed directly into silk channel of selected ears on 6 different days (days 3, 6, 9, 12, 15, and 18 after first silk). The same six ears were then harvested 4 days later.
Raising corn earworm. This experiment was started early in the growing season to avoid wild populations of CEW in the field; hence, laboratory-raised larvae were used.

Sixty-four pupal stage insects were shipped to the University of Massachusetts from the USDA Southern Insect Management Research Laboratory collection (Stoneville, Miss.) on 5 April 2000 and 7 May 2001. The pupae were placed in containers (Solo, Inc., Chicago, Ill., 473 mL cup #116MR with plastic lid #624-P) and kept in a rearing room at a constant temperature of 25 °C. Male and female pupae were separated and kept in the cups until the moths emerged.

As the moths emerged from the pupal casings, they were transferred into new cups to mate, along with a strip of dental wicking (Richardson Dental, Charlotte N.C.) immersed in a sugar water solution (10% sucrose solution mass:volume) for feeding.

Each cup with breeding moths was covered by a mesh metal screen (with 1 mm squares) that provided a structure for the females to hold when they laid eggs and a paper towel. Eggs were collected by removing the paper towel and placing it over another cup (Solo 148 mL #TS-5 with lid #662-P) that was filled with a commercially purchased CEW diet (Southland Company, Lake Village, Ark.: 163 mL of dry diet mixed with 900 mL H2O and 7 mL raw linseed oil). The cups were numbered with the date that the eggs were laid.
Larval emergence is temperature dependent, as are other stages of the CEW life cycle (Butler, 1976). In a room at 21 °C, the eggs took approximately 2 to 3 days to hatch. To manipulate hatching time, eggs were placed in a refrigerator at 13 °C, then moved to 21 °C to progress them towards hatching. Adjustments were made to rearing temperatures to slow or speed the development of the colony. The goal was to have a minimum of 400 first-instars available to use in the field experiment every 3 days over a 15 day period.

Planting and experimental design, Year 1. A 70 m x 25 m (331 ft. x 119 ft.) portion of a grower’s cornfield in Deerfield, Massachusetts was rented for this research. The grower took responsibility for all field work until the corn was approximately 10 days away from first silk. After that time, he did not enter the plots nor spray any pesticides within 7 m (approximately 25 ft.) of the experimental area.

The soil type in the first year was a Limerick silt loam (coarse silty, mixed, mesic). The corn cultivar “Temptation” (Sieger’s Seed Company, Zeeland, Mich.) was planted on 20 April 2000 and grown using standard sweet corn production practices except that no pesticides were used. The field was irrigated as deemed necessary by the farmer.

Plots were four rows wide on 1.2 m (4 ft.) centers with two outer rows as guard rows. This was a split-plot design with eight replications. Each main plot was 11 m (36 ft.) long and each sub-plot was 1.8 m (6 ft.) long. The main plot was the four pesticide treatments: 1) an untreated plot (no oil and no Bt); 2) Stop & Shop brand corn oil; 3) Dipel DFÒ [Bacillus thuringiensis, Berliner, subs. Kurstaki; (Valent Agricultural Products, Richardson, Texas)]; and 4) oil + Bt. Pesticide treatments were applied on silk day 5 (18 July 2000). Silk day 1 (13 July 2000) was designated as the day that a minimum of 50% of the corn ears (only the primary ear was used on each stalk) within the experimental area had approximately 2.5 cm (1 in.) of silk protruding from the ear (Adams and Clark, 1996).

Within each main plot were six split-plots delineating larvae application days (silk days 3, 6, 9, 12, 15, and 18. Six ears were chosen randomly in each sub-plot and labeled. Two first-instar larvae were laid near the opening of the silk channel with a soft-tipped paintbrush at 1000 hr on the appropriate day. Preliminary data showed that four days was sufficient time for larvae to move into the silk channel and feed.
The pesticide treatments were applied at 1030 hr on silk day 5. The oil and Bt mixture was prepared, and applied using the zea-later, as described in the methods for Objective 1. The Zea-later® was used to deliver 0.5 mL of suspension directly into the silk channel of each corn ear. All liquids were agitated manually and regularly during application to keep materials in suspension.

The same six ears from each plot were harvested 4 days after each larvae application (silk days 7, 10, 13, 16, 19, and 22). Day 22 also represented the day a grower would normally harvest ears for market (milk stage). The ears were placed in bags, then immediately taken to the laboratory for evaluation. The ears were inspected for signs of damage caused by larval feeding, and for the number of live CEW. Caterpillar damage was assessed as in Objective 1. Total ear and cone tip length (area of undeveloped kernels) was also measured. Cone tip was expressed as a percent of total ear length. The number of marketable ears was based on a percentage of ears receiving a damage rating of 0. Cone tip was not used as a criterion for marketability.
Planting, Year 2. A different piece of land in Deerfield, Massachusetts was rented from the same grower as in 2000. In year 2, “Peto 6803” (Sieger’s Seed Company, Zeeland, Mich.) was planted into a Hadley loam (coarse-silty, mixed, mesic) on 1 May 2001.

In year 2, silk day 1 was 8 July 2001. The four pesticide treatments were applied on 12 July. Larval application (days 3, 6, 9, 12, 15, and 18) and harvest (7, 10, 13, 16, 19, and 22) took place on the same silk days as the first year. All other aspects of the fieldwork in 2001 were conducted in the same manner as noted above in 2000.

Monitoring and foliar sprays. WarriorÒ [lamda-cyhalothrin (Zeneca Agrochemical Products, Wilmington, Del.) was applied on 20 June and 29 June 2001 at a rate of 30 mL.ha-1 (0.24 lb active ingredient per acre) to combat high numbers of European corn borers in the tassel prior to silk initiation. Moth flights and caterpillar infestations were monitored using the same protocols as in the other trials after silk initiation.

Data analysis. The data from six ears in each split-plot for the four treatments and eight replications for this factorial experiment (treatment x time) were analyzed using the general linear model (GLM) of SAS (SAS v.8.2 for Windows, SAS Institute, Cary, N.C.).

Research results and discussion:
OBJECTIVE 1

In the 2000 and 2001 growing seasons 37 experimental plantings of corn were successfully grown, treated with oil, and harvested. An additional 20 plantings of corn from 1999 are included in the results. Plantings were subject to a wide range of field conditions and pest pressure. The 2000 season was very wet and cold resulting in poor crop emergence and slow growth, and there was significant pest pressure from CEW and ECB. The 2001 season was drier and hot with almost no CEW pressure, except on coastal farms.

Oil treatments gave statistically significant improvements in the percent of marketable ears and tip damage ratings on all farms for almost every planting. An analysis of all of the blocks on all of the farms shows a statistically significant increase in the percentage of clean, marketable corn in the treated (oiled) verses the untreated samples for each year of the experiment: the overall mean improvement in the percentage of clean ears between the untreated and the oiled ears for all plantings on all of the farms was 21.6% and ranged from 0-56% (Figure 1), with the highest levels of improvement generally occurring on farms with the greatest pest pressure. Significant reductions were also achieved in the number of caterpillars found and in the percent of ears with side damage. The number of plantings with differences in the amount of side damage between the treated and untreated ears decreased in the last year of the project, which we attribute to the more consistent application of the Bt foliar sprays to reduce European corn borer tunneling through the side.

The number of clean ears was defined to be the number of corn ears that had no damage to the kernels. If there was damage to the kernels from caterpillars entering either through the tip or the side of the ear it was considered unmarketable for the purposes of this study. Figure 2 shows the average percent of clean ears on each farm for the 3 growing seasons from 1999-2001. Of the eight farms that participated, five were able to achieve a 3-year average of over 80% clean ears with the oiling. Out of all of the plantings (57), 30% more of the blocks achieved >80% clean ears in the oil-treated versus the untreated blocks of corn. The number of blocks of corn that had >90% clean ears increased by 18% between the untreated and oil-treated blocks.

Most farms demonstrated a trend toward better control over the course of the three years. Both 1999 and 2000 had substantial corn earworm pressure on all farms, while in 2001 low corn earworm pressure resulted in an increase in the number of clean ears in the untreated and treated blocks in most plantings. Greater numbers of clean ears in all years were also due to improved timing, materials and equipment, better use of Bt sprays for ECB control, and growers’ increasing familiarity with the method.

One of the farms that had very good control using the bio-intensive system is Brookfield Farm. The caterpillar populations on this farm include both CEW and ECB, the relative numbers of which vary throughout the season. Together they cause significant damage to late corn. Non-oiled corn ranged from 7% clean to 78% clean during 1999 and 2000, when no foliar Bt sprays for ECB were applied. In these two years, oiled corn averaged 78% clean in 1999 and 91% clean in 2000 (Figure 4), with an average improvement of 30% due to oiling.

In the final year of the project, when all blocks were sprayed with Bt for ECB control, and CEW pressure was relatively low, this farm had >91% clean ears in the oiled corn. This was partly due to the Bt sprays to reduce side damage, as seen in the yearly average of 82% clean ears in the control, non-oiled corn that had Bt foliar sprays, compared to 46% clean in 1999 and 64% clean in 2000, years in which no foliar sprays were applied. Increases through foliar sprays in the number of clean ears helps to increase the success rate in oiled corn. Also, increases in the number of clean ears through the project can be attributed to improvements in the oil + Bt mix and the improved Zea-later application device.

Kestrel Farm highlights how the effectiveness of the bio-intensive control system depends upon the control of ECB as well as CEW. The oil treatment is aimed at preventing damage to the tip by blocking the silk channel with oil and coating the tip of the ear with oil and Bt. While it was designed to control the CEW it is also effective against ECB or fall armyworm (FAW) attempting to enter the ear through the tip. To achieve acceptable levels of control of caterpillars that tunnel through the husk into the side of the ears (ECB &FAW) the foliar sprays should be used as well.

Most of the caterpillar damage on Kestrel farm is due to the European corn borer: corn earworm pressure is relatively low. ECB moths (>45/night) consistently far outnumbered corn earworm moths (2 or less per night), and the actual caterpillars found in the corn were mostly ECB. For example, in 2000, the ratios of ECB to CEW found in 100 ears of non-oiled corn in the three blocks were 75 ECB:5 CEW in planting one, 110:10 in planting 2, and 180:5 in planting 3 (Figure 5). In these blocks, oiling produced 88%, 60%, and 70% clean corn, respectively, for a seasonal average of 72% clean (an improvement of 17% compared to non-oiled corn). Given the numbers of ECB caterpillars in the corn, one would expect that most of the damage would be from ECB entering through the side of the ears. Yet, as can be seen in Figure 6, while there is a substantial amount of side damage in the oiled corn, there is also a significant amount of tip damage despite the low numbers of CEW. This indicates that the ECB enter from the tip of the ear as well as eat through the side.

When the grower saw these results at the winter meeting, he realized the value of focusing more on using Bt sprays to prevent ECB damage. A second foliar Bt spray was added to the trials in the 2001 growing season. The first one was applied in the tassel stage while the second was applied during early silk. Sprays were applied to the whole field and are therefore reflected in the data for the untreated control, as well as the oil treated corn. At Kestrel Farm, ECB moth captures in 2001 were comparable to those in 2000, but the number of ECB caterpillars found in the non-oiled corn ears was much less in 2001 (2, 82, and 57 ECB per 100 ears in each of the three blocks) (Figure 7). The number of corn ears with caterpillar damage was correspondingly lower, with all blocks (both oiled and non-oiled) having <15% damage, and the oiled blocks averaging 95% clean and marketable ears compared to 91% in the non-oiled. This shows that in situations where ECB is a problem, using control measures such as foliar Bt sprays are critical to obtaining clean and marketable corn. Further, while the oil treatment is targeted to the damage caused by CEW in the tip, the results from Kestrel Farm show that the oil treatments reduce the damage and number of ECB caterpillars as well (Figures 5-7).

Wishing Stone Farm demonstrates a different extreme in pest pressure. This Rhode Island farm is on the southern coast of New England in the migratory flight path of CEW moths and is subject to flights that arrive early, continue all season, and cause extremely high levels of corn earworm infestations each year. In this region conventional growers apply insecticide at three, or sometimes two-day intervals throughout silking. At the outset we knew that this farm would present the greatest challenge to the bio-intensive system.

While the intense corn earworm pressure on Wishing Stone Farm does vary, the CEW moth captures were nearly always greater than the threshold of two moths per week throughout the experiment. In August and early September captures exceeded 5 moths per night during all three years (Appendix A, Table 1). In the first planting of 2000 the CEW trap captures on Wishing Stone Farm reached a high of 44 per night (that’s over 300 per week!), which resulted in heavily infested corn that had an average of two CEW caterpillars per ear of corn (see Figure 8, Block 1, Control) and nearly 100% damage to the corn (Figure 9, Block 1, Control).

During the course of the project on Wishing Stone Farm, non-oiled corn had, at the best, 25% clean ears, and at the worst, 0 % clean ears. Even in 2001, when most growers had little to no CEW pressure, the non-oiled corn at Wishing Stone Farm had corn earworm in just about every ear (Figure 10). In contrast to the 401 caterpillars found in the non-oiled corn on Wishing Stone Farm, there were only 206 caterpillars in all of the non-oiled corn on all of the other farms combined (94 of which were from one farm). This resulted in 10 out of 12 plantings on all of the other farms in 2001 having greater than 82% clean ears in the non-oiled plots, while Wishing Stone Farm had less than 10% clean ears combined that year.

Although the grower was unable to achieve 80% clean ears in the three years of the experiment, the greatest improvements in the numbers of clean ears were obtained on this farm. The farmer had significant reductions in the number of caterpillars and percent of clean ears (high of 59%, low of 21%) in his oil-treated corn. The greatest increase in clean ears between the untreated and oiled samples was achieved on this farm in 2000 (59%). Skip’s best results were obtained in 2001 when he oiled a different variety (Argent) at the same time he was treating the Delectable for the on-farm trials. In this corn he achieved 76% clean ears, his highest number, compared to 32% clean in the un-oiled corn of that variety.

The data from Wishing Stone Farm in 2001 (Figure 10) suggests that a tighter-husked variety can reduce the amount of corn earworm that can get into the ears. The sub-sample of the cultivar Argent, which had a tighter husk than the Delectable variety used in the trials, was planted at the same time as the second planting of Delectable in 2001. The Argent had more clean ears in the control (8/25=32%) verses the Delectable (2/100=2%), and a greater improvement in clean ears in the oil treated corn (44% improvement; 19/25=76% clean) than in the Delectable (24% improvement; 26/100=26% clean). This is a strong indication that other factors, such as variety of corn planted, may make a large difference in the effectiveness of the oil treatments. Use of a tight-husked variety, along with Bt foliar sprays and oil could together provide adequate control under these high-pressure circumstances.

It is also likely that other factors played a role in the relatively low numbers of clean ears obtained in oiled corn on this farm. One of the largest factors may have been weed control. The fields in which corn was planted were far from the rest of the farm, thus good timing of weed control was difficult. Further, fields were filled with large stands of jimsonweed, which not only gets very tall, but contains narcotic-poisonous oils as well. Thus there was a large physical barrier within the corn planting that prevented workers from walking through the field and reaching every ear. For the purposes of our experiment, however, enough oiled ears were obtained for data collecting purposes.

The other farm that had problems getting clean corn had never grown corn before, and had difficulty with fertility and raccoons. Results were obtained for one block each in 2000 and 2001. The stand sizes were also very small compared to the stands on other farms, which may or may not affect the susceptibility of each ear to caterpillar infestation. Healthier corn, larger stands and more practice with the method will likely improve their results.

OBJECTIVE 3, EXPERIMENT 1:

RESULTS

Trap counts and populations. During both plantings in each year, CEW and ECB moth captures were sufficient to result in damage to the sweet corn, with non-oiled ears ranging from 30-77% marketable in the four plantings. CEW flight was higher in 2000 than in 2001; however, populations were moderate in both years. ECB flights were higher in 2001 than in 2000; however, larval numbers were higher in 2000, possibly because the pre-silk Bt spray reduced infestations that originated prior to silking. In 2000 the captures of CEW moths were higher in the early planting than in the late, while in 2001, CEW moths were more numerous for the late planting. In both years, ECB larvae were more numerous than CEW larvae, but this difference was more pronounced in 2000.

Corn earworm. Corn earworm larvae were generally found in the silks or in the first inch of the ear. Table 2 shows the number of larvae and the degree of feeding damage they caused, averaged over the two planting dates for 2000 and 2001. Comparing non-oiled corn to the average mean of all treatment dates, there were significantly more live corn earworm found in the non-oiled ears as were found in treated ears in both plantings in both years (Table 1). In three of the four plantings oiling reduced corn earworm numbers by more than threefold; and in the fourth, by almost twofold.

In 2000 the number of live CEW larvae found in the ears was significantly lower than the control on all treatments days (P £ 0.05) and there was a significant positive linear relationship between the number of CEW larvae and the day of treatment (p=0.0190). In 2001 the number of CEW larvae was significantly lower on days 3, 4, 5, 7, 8, and 10 compared to untreated ears, and there was no linear relationship between treatment day and the number of CEW larvae.

European corn borer. Most European corn borers were found in the area 2.5 cm below the tip of the ear and were accompanied by evidence of a side entry hole in the husk or the shank. More European corn borers were found per ear than corn earworm, especially in 2000 when no foliar sprays for corn borer were applied. Overall the oil treatment significantly reduced the number of live ECB larvae found per ear. Compared to non-oiled ears, application on any day significantly reduced the number of live ECB larvae found per ear in 2000 and on days 3, 4, 6, 7, 10, and 11 in 2001 (Table 1). Comparing non-oiled corn to the average mean of all treatment dates, there were at least 5-fold more live ECB larvae found per ear in 2000 in the untreated ears and at least 2-fold more live ECB larvae per ear in the untreated ears in 2001.

Feeding damage. Mirroring the results of the number of live caterpillars, the degree of feeding damage to the tip of each ear was significantly higher in the untreated control in both 2000 and 2001 compared to the mean of all treatment dates. In the untreated ears, tip damage or frass was found primarily evident in the silks or in the first 2.5 cm of tip of the ear, resulting in damage ratings of 1 or 2 (Table 1). All application days in both years had significantly less tip damage compared to the control. The degree of damage increased linearly with later application dates in 2001 (p=0.0017), but not in 2000.

Side and husk damage. There was a significant linear relationship between application date and both side and husk damage in 2001 (p=0.0002 and p = 0.0072, respectively), but not in 2000. The later the treatment was applied, the more entry holes were found in the husk and more side damage to the ear (Table 2). However, for both side and husk damage, very few of the application dates were significantly different from the non-oiled control in either year.

Percent Cone-Tip. Earlier applications had a greater effect on kernel development than those applied later in the silking period (Table 2). The percent of the ear with cone-tip decreased linearly with the day of treatment application and this effect was consistent over all plantings (p<0.0001). At its most severe, over 20% of the ear was affected (application on Day 3, early planting, 2000). In the late planting of 2001, the earliest application (Day 3) produced slightly less than 12% cone-tip.

In 2000, the percentage of cone-tip was not significantly different from the untreated control by day nine. In 2001, this point was reached by day 6. In separate analyses of the two planting dates for each year, the earliest that cone-tip reached the level found in untreated ears was Day 6, and the latest was Day 10 after 50% silk initiation.

Caterpillar size. Further analysis will include effects of treatment date on insect size. Preliminary statistics suggest that larval size was greater in later treatment dates.

DISCUSSION (EXPERIMENT 1)

This study did not specifically address or determine what degree of cone-tip would be accepted or rejected in retail or wholesale markets. In current hybrid SE cultivars, kernels normally develop all the way to the tip unless the corn is drought-stressed during ear development. Growers using oil have rarely complained about the cone-tip, stating that their customers would much prefer a slightly undeveloped tip to a tip filled with a caterpillar and frass. However, the fully filled ear is the ideal, and the extreme level of cone-tip found on early application dates (Day 3-4, percent cone averaging 10-20% of the ear) are clearly not as desirable as a well-filled ear.

The silks at the tip usually did not detach from the kernels as they did further down the ear. This lack of detachment suggests that fertilization does not take place. We theorize that oil coats the trichomes on the silks, thus affecting either the ability of the trichomes to capture pollen or the ability of the pollen tube to penetrate and/or grow through the silk to the egg (Carter, personal communication). The oil itself could be phytotoxic to the silk tissue, though no abnormal desiccation, wilting, or discoloration was observed in the silks. The silks felt only very slightly oily to the touch.

An additional experiment was conducted (see Experiment 3, below) to study kernel growth over time and how this was affected by oil or other interruptions of pollination such as covers over the silk. The results suggest that the most critical period for pollination is between day 0 and day 3, and application of oil during these first three days of silking grossly inhibits the development of kernels. After that, normal tip development occurs in increasing degrees. This is consistent with what we found in this experiment. Thus, based simply on tip development, treatment should be delayed at least until after day 4, and later if possible.

This experiment was less clear in pinpointing a treatment day to achieve the best insect control. Application on any day decreased the number of larvae present compared to the control. Caterpillar feeding damage ratings fluctuated over the nine treatment days for both planting dates in 2000 and the early planting date in 2001. However, in 2000, CEW numbers increased over time, and in 2001 tip damage increased over time. Thus it would appear that in many cases any application date would give significant control, though the best application date would be the earliest time when cone-tip would not be unacceptably severe.

Earlier research found that there was a corresponding increase in feeding damage to the corn tip when oil treatments were applied after day 5 (Siedlecki, 1996). Oil is able to control both larvae entering the silk channel after the treatment is applied, as well as those larvae present in the ear prior to treatment, though any damage caused by these larvae is, of course, irreversible. In Experiment 2, oil + Bt solution was effectively able to control larvae entering the silk channel for up to 22 days after application (Experiment 2: Cook, et al., 2003). In that experiment, somewhat less effective control was found when larvae were present before the oil application.

When the presence of the European corn borer was considered alone, treated plots clearly showed a much lower number of European corn borer versus the number found in the untreated plots.

Although the direct oil treatment may not give full control European corn borer control in the field, visual observations showed that they often backed out of the husk once they encountered the oil barrier and did not feed on the ears. Also, many ECB enter the ear through the silk channel and are, therefore, controlled by the oil treatments. This result is consistent with what we found in grower trials.

Hazzard (1997) suggested that the use of an oil barrier consistently yielded 2-3 times more undamaged ears when compared to untreated areas. This study also showed that a higher percentage of clean ears were found when Bt was used as a foliar spray in addition to the oil/Bt direct silk application.

In summary, a direct silk application of oil + Bt after pollination is complete, on days 5 – 7 from first silk, should provide the best combination of decreased damage to the ear caused by European corn borer and corn earworm, and increased marketability due to the best tip fill in the ear.

OBJECTIVE 3, EXPERIMENT 2:

RESULTS

Because weather and cultivar affected the time of silking, and coordinating the time of silking with the time of larval development was difficult, the cultivar used for the experiments could not be controlled. Thus, two different corn cultivars were used in 2000 and 2001. Due to the differences in temperature, rainfall, soil types, and cultivars between year 1 and year 2 of this experiment, the data for each year were analyzed separately. The general treatment effects averaged over the six larval placement dates, are shown in Figure 11 for the number of live larvae found per ear (Figure 11A) and the level of damage per ear caused by larval feeding (Figure 11B). Overall, the use any treatment decreased the number of live larvae found and the degree of feeding damage compared with the untreated control (no oil, no Bt). Though not additive, the oil + Bt combination resulted in the highest level of control overall and the least amount of feeding damage.
Corn earworm. The main effects of time, oil, and Bt were significant in 2000 and 2001 (Table 3).

Time did not interact with oil to significantly affect the number of CEW so this data was not presented, but time did interact significantly with Bt and a separation of means was performed for this effect (Figure 2). Results of the comparison of means showed that the use of Bt was significant on 4 of the 6 harvest days in 2000. The number of live CEW found on ears without Bt applications were almost four times as high as the number of live CEW found on ears treated with Bt.

In 2001, the use of Bt was significant on 5 of the 6 harvest days. Differences were non-significant only on the first harvest day (silk day 3) perhaps due to the fact that larvae had been exposed to treatments for only 2 days when these ears were analyzed. For larval placement dates 6, 9, 12, 15, and 18, there was an approximately five-fold greater number of live CEW in treatments without Bt than in those with Bt; thus, the use of Bt as a treatment provided significantly improved protection against corn earworm larvae compared to treatments without Bt.

Damage. Recorded damage ratings ranged between 0 and 2, meaning that until the last 2 harvest dates, larvae were rarely found further down than 2.5 cm (1 in.) from the tip of the ear. Most of the CEW were found in the silk above the ear. Part of this is due to that fact that in the early stages of ear growth, the ear is still elongating. Since larvae find ample silks to feed on, larvae tend not to move towards the developing ear.

The three main effects, time, oil, and Bt were significant (Table 3). Oil interacted with time to affect the damage rating per ear (Figure 13) while Bt and time did not interact significantly in either 2000 or 2001 (data from this mean separation is thus not shown). The oil treatment was more effective in suppressing larval damage on days 9, 12, 15, and 18 in both years. In 2001, the level of damage increased over time in the untreated ears compared to the oil treated ears.

Cone tip. In 2001 cone tip was observed and recorded (Table 4). Cone tip length measured in this year was longer in all treated ears compared to untreated ears. Ears receiving only Bt as a treatment had a mean cone tip length of 0.06 cm (0.02 in.) or 0.3% of the entire ear length, compared to 0.01% of the entire length in untreated ears. The oil treatment had a mean cone tip length of 1.24 cm (0.49 in.) or 6.5% of the ear, but the oil and Bt mixture recorded the highest reading of 1.69 cm (.67 in.) or 9.1 % of the ear. Clearly, oil had a greater effect on kernel development than Bt.

Marketable ears. Marketable ears were those that received a rating of 0 based on the damage scale used in this experiment. Cone tip was not used as a criterion for marketability. For both years, the number of marketable ears was highest in the plots treated with oil and oil plus Bt (Table 4). In comparison, Bt alone provided 88 and 83% marketable ears, while only 73 and 46% of the untreated ears were marketable in 2000 and 2001, respectively.

DISCUSSION

Untreated ears had more live CEW and higher levels of feeding damage than the other three treatment ears for all harvest days in both years. The number of CEW found per ear was lower when Bt was included in the treatment. The use of corn oil gave the lowest damage ratings on almost all harvest days in both years.

Treatments which contained oil had the highest number of marketable ears in both years, but also the highest percentage of underdeveloped kernels at the tip of the ear (6 to 9%). The oil and Bt treatments appeared to control CEW for at least 17 days, from silking through maturity. This treatment regime appears to be a promising alternative for growers to conventional pest management methods.

Although the actual number of live CEW found varied between the two years, the effects were similar. Though there were more live larvae found in year one than in year two, the untreated ears always had greater numbers of larvae than either of the treatments. Carruth (1942) and Hazzard (1997) found similar results, though only a single harvest was made at the milk stage of the ear in these experiments. Most CEW caterpillars and damage were found in the silks during the first three harvest days after treatment; this is most likely because the ears are short in the early stages of development and CEW feed on silks as well as kernels, leaving little reason for CEW to continue to move towards the developing ear. The level of damage increased over time as the ear grew and became more accessible to the larvae.

It appears that Bt is more effective at killing CEW than oil. One study in a petri dish showed that CEW was more likely to avoid areas with oil, but pass through areas with Bt (Pam Westgate, personal communication). It is not known whether this type of avoidance can occur within the silk channel or not. Visual observation of the silks treated with oil indicates that all silks are coated equally with oil throughout the husk, whereas when Bt is used alone (in a water solution) it sometimes beads up at the entrance to the silk channel. Since the mode of action of oil (we believe by asphyxiation) and Bt (stomach poison) are different, it should not be surprising that their effectiveness as treatments are somewhat different.

The oil appeared to have greater damage deterrence and for a longer period of time than Bt. As most corn takes 20 days or more to reach maturity once silks emerge, the longevity of treatment is an important factor. One farmer estimated that it took approximately 8 hours to oil one acre of corn (D. Kaplan, grower, personal communication). Organic growers, with few other options for controlling CEW in the silks, indicated that a single application is cost effective in that the increase in marketable ears compensates for the cost of the labor (S. Mong, Mass. grower, J. Manix, Vt. grower, personal communication).

Cone tip lengths were impacted in year 1 by the unusual cold and wet weather occurring in that growing season. In year 2, cone tip among the different treatments was more typical of what was observed in other studies (Carruth, 1942; Hazzard and Gault, 1993; Hazzard, 1994). Oiled ears had the highest percentage of cone tip on each ear. The silks at the tip of the ear (approximately the last ten rings of kernels from the tip) are the last to emerge and the tips are often still inside the silk channel when the oil is applied.

Typically, some portion of the tip is unfilled, even in untreated ears. Carruth (1942) suggested that 1.25 cm (0.5 in.) of cone tip was normal in an untreated ear, although modern varieties are expected to have complete fill all the way to the ear. Cone tip was not used as a criteria to determine marketability because consumer reaction to cone tip is also variable (Hazzard, personal communication). Growers who sell through direct markets such as farm stands and farmers’ markets in New England are able to explain cone tip to their customers. The explanation seems acceptable to consumers, especially those who prefer organically grown corn. Contact with consumers through the wholesale market, however, is not possible. Growers or retail packers who pre-package partially husked ears simply cut the tip off prior to packaging. However, further research to find ways to prevent the cone tip is worthwhile.

The data from this experiment appears to support the current recommendations from the University of Massachusetts for CEW control using direct silk application of oil and/or Bt (Hazzard, 1998; 2002). It also appears that the treatment is effective from silk day five through maturity and thus is a promising method for CEW control, especially for organic growers.

OBJECTIVE 3, EXPERIMENT 3:

ABSTRACT

Field studies were conducted in 2001 to measure the physical effects of direct oil treatments on physiological development of sweet corn ears, Zea mays (L.), when oil was applied on 9 different days. The different treatment regimes included: 0.5 mL of corn oil applied directly to the silk channel of the ears using a Zea-later® on silk days 3 through 11; brown bags (to block pollination) placed over ears on silk days 3 to 11; bags placed over ears on day 0 and removed on day 3 to 11 with oil applied at this time; oil applied on day 3 through 11 with a bag placed over the ear on that same day; and no treatment. Silk day 1 is the first day when 50% or more of the corn has 2.5 cm of silk emerging from the ear. Results showed that only the treatment with a bag covering the ear from day 0 showed significant differences in ear development on most days compared to all other treatments. These ears showed significantly lower ear weight, kernel weight, and number of kernels when compared to all other treated and untreated ears. Among the other treatments, covering ears with a bag on day 3 through 11 showed very similar results to the use of the direct oil application but these results were not significantly different from the untreated ears. It appears that the most critical period for pollination is between day 0 and day 3 and supports other research, which recommends not using direct silk application prior to day 5. Also, it appears that corn oil does not completely block the pollination and fertilization process. The results suggest that the application of oil during the first three days of silking grossly inhibits the development of kernels, but after that, normal tip development occurs in increasing degrees.

OBJECTIVE 2

See Economic Analysis

OBJECTIVE 3: EXPERIMENT 1

RESULTS

Trap counts and populations. During both plantings in each year, CEW and ECB moth captures were sufficient to result in damage to the sweet corn, with non-oiled ears ranging from 30-77% marketable in the four plantings. CEW flight was higher in 2000 than in 2001; however, populations were moderate in both years. ECB flights were higher in 2001 than in 2000; however, larval numbers were higher in 2000, possibly because the pre-silk Bt spray reduced infestations that originated prior to silking. In 2000 the captures of CEW moths were higher in the early planting than in the late, while in 2001, CEW moths were more numerous for the late planting. In both years, ECB larvae were more numerous than CEW larvae, but this difference was more pronounced in 2000.

Corn earworm. Corn earworm larvae were generally found in the silks or in the first inch of the ear. Table 2 shows the number of larvae and the degree of feeding damage they caused, averaged over the two planting dates for 2000 and 2001. Comparing non-oiled corn to the average mean of all treatment dates, there were significantly more live corn earworm found in the non-oiled ears as were found in treated ears in both plantings in both years (Table 1). In three of the four plantings oiling reduced corn earworm numbers by more than threefold; and in the fourth, by almost twofold.

In 2000 the number of live CEW larvae found in the ears was significantly lower than the control on all treatments days (P £ 0.05) and there was a significant positive linear relationship between the number of CEW larvae and the day of treatment (p=0.0190). In 2001 the number of CEW larvae was significantly lower on days 3, 4, 5, 7, 8, and 10 compared to untreated ears, and there was no linear relationship between treatment day and the number of CEW larvae.

European corn borer. Most European corn borers were found in the area 2.5 cm below the tip of the ear and were accompanied by evidence of a side entry hole in the husk or the shank. More European corn borers were found per ear than corn earworm, especially in 2000 when no foliar sprays for corn borer were applied. Overall the oil treatment significantly reduced the number of live ECB larvae found per ear. Compared to non-oiled ears, application on any day significantly reduced the number of live ECB larvae found per ear in 2000 and on days 3, 4, 6, 7, 10, and 11 in 2001 (Table 1). Comparing non-oiled corn to the average mean of all treatment dates, there were at least 5-fold more live ECB larvae found per ear in 2000 in the untreated ears and at least 2-fold more live ECB larvae per ear in the untreated ears in 2001.

Feeding damage. Mirroring the results of the number of live caterpillars, the degree of feeding damage to the tip of each ear was significantly higher in the untreated control in both 2000 and 2001 compared to the mean of all treatment dates. In the untreated ears, tip damage or frass was found primarily evident in the silks or in the first 2.5 cm of tip of the ear, resulting in damage ratings of 1 or 2 (Table 1). All application days in both years had significantly less tip damage compared to the control. The degree of damage increased linearly with later application dates in 2001 (p=0.0017), but not in 2000.

Side and husk damage. There was a significant linear relationship between application date and both side and husk damage in 2001 (p=0.0002 and p = 0.0072, respectively), but not in 2000. The later the treatment was applied, the more entry holes were found in the husk and more side damage to the ear (Table 2). However, for both side and husk damage, very few of the application dates were significantly different from the non-oiled control in either year.

Percent Cone-Tip. Earlier applications had a greater effect on kernel development than those applied later in the silking period (Table 2). The percent of the ear with cone-tip decreased linearly with the day of treatment application and this effect was consistent over all plantings (p<0.0001). At its most severe, over 20% of the ear was affected (application on Day 3, early planting, 2000). In the late planting of 2001, the earliest application (Day 3) produced slightly less than 12% cone-tip.

In 2000, the percentage of cone-tip was not significantly different from the untreated control by day nine. In 2001, this point was reached by day 6. In separate analyses of the two planting dates for each year, the earliest that cone-tip reached the level found in untreated ears was Day 6, and the latest was Day 10 after 50% silk initiation.

Caterpillar size. Further analysis will include effects of treatment date on insect size. Preliminary statistics suggest that larval size was greater in later treatment dates.

DISCUSSION

This study did not specifically address or determine what degree of cone-tip would be accepted or rejected in retail or wholesale markets. In current hybrid SE cultivars, kernels normally develop all the way to the tip unless the corn is drought-stressed during ear development. Growers using oil have rarely complained about the cone-tip, stating that their customers would much prefer a slightly undeveloped tip to a tip filled with a caterpillar and frass. However, the fully filled ear is the ideal, and the extreme level of cone-tip found on early application dates (Day 3-4, percent cone averaging 10-20% of the ear) are clearly not as desirable as a well-filled ear.

The silks at the tip usually did not detach from the kernels as they did further down the ear. This lack of detachment suggests that fertilization does not take place. We theorize that oil coats the trichomes on the silks, thus affecting either the ability of the trichomes to capture pollen or the ability of the pollen tube to penetrate and/or grow through the silk to the egg (Carter, personal communication). The oil itself could be phytotoxic to the silk tissue, though no abnormal desiccation, wilting, or discoloration was observed in the silks. The silks felt only very slightly oily to the touch.

An additional experiment was conducted (see Experiment 3, below) to study kernel growth over time and how this was affected by oil or other interruptions of pollination such as covers over the silk. The results suggest that the most critical period for pollination is between day 0 and day 3, and application of oil during these first three days of silking grossly inhibits the development of kernels. After that, normal tip development occurs in increasing degrees. This is consistent with what we found in this experiment. Thus, based simply on tip development, treatment should be delayed at least until after day 4, and later if possible.

This experiment was less clear in pinpointing a treatment day to achieve the best insect control. Application on any day decreased the number of larvae present compared to the control. Caterpillar feeding damage ratings fluctuated over the nine treatment days for both planting dates in 2000 and the early planting date in 2001. However, in 2000, CEW numbers increased over time, and in 2001 tip damage increased over time. Thus it would appear that in many cases any application date would give significant control, though the best application date would be the earliest time when cone-tip would not be unacceptably severe.

Earlier research found that there was a corresponding increase in feeding damage to the corn tip when oil treatments were applied after day 5 (Siedlecki, 1996). Oil is able to control both larvae entering the silk channel after the treatment is applied, as well as those larvae present in the ear prior to treatment, though any damage caused by these larvae is, of course, irreversible. In Experiment 2, oil + Bt solution was effectively able to control larvae entering the silk channel for up to 22 days after application (Experiment 2: Cook, et al., 2003). In that experiment, somewhat less effective control was found when larvae were present before the oil application.

When the presence of the European corn borer was considered alone, treated plots clearly showed a much lower number of European corn borer versus the number found in the untreated plots.

Although the direct oil treatment may not give full control European corn borer control in the field, visual observations showed that they often backed out of the husk once they encountered the oil barrier and did not feed on the ears. Also, many ECB enter the ear through the silk channel and are, therefore, controlled by the oil treatments. This result is consistent with what we found in grower trials.

Hazzard (1997) suggested that the use of an oil barrier consistently yielded 2-3 times more undamaged ears when compared to untreated areas. This study also showed that a higher percentage of clean ears were found when Bt was used as a foliar spray in addition to the oil/Bt direct silk application.

In summary, a direct silk application of oil + Bt after pollination is complete, on days 5 – 7 from first silk, should provide the best combination of decreased damage to the ear caused by European corn borer and corn earworm, and increased marketability due to the best tip fill in the ear.

OBJECTIVE 3: EXPERIMENT 2

RESULTS

Because weather and cultivar affected the time of silking, and coordinating the time of silking with the time of larval development was difficult, the cultivar used for the experiments could not be controlled. Thus, two different corn cultivars were used in 2000 and 2001. Due to the differences in temperature, rainfall, soil types, and cultivars between year 1 and year 2 of this experiment, the data for each year were analyzed separately. The general treatment effects averaged over the six larval placement dates, are shown in Figure 11 for the number of live larvae found per ear (Figure 11A) and the level of damage per ear caused by larval feeding (Figure 11B). Overall, the use any treatment decreased the number of live larvae found and the degree of feeding damage compared with the untreated control (no oil, no Bt). Though not additive, the oil + Bt combination resulted in the highest level of control overall and the least amount of feeding damage.
Corn earworm. The main effects of time, oil, and Bt were significant in 2000 and 2001 (Table 3).

Time did not interact with oil to significantly affect the number of CEW so this data was not presented, but time did interact significantly with Bt and a separation of means was performed for this effect (Figure 2). Results of the comparison of means showed that the use of Bt was significant on 4 of the 6 harvest days in 2000. The number of live CEW found on ears without Bt applications were almost four times as high as the number of live CEW found on ears treated with Bt.

In 2001, the use of Bt was significant on 5 of the 6 harvest days. Differences were non-significant only on the first harvest day (silk day 3) perhaps due to the fact that larvae had been exposed to treatments for only 2 days when these ears were analyzed. For larval placement dates 6, 9, 12, 15, and 18, there was an approximately five-fold greater number of live CEW in treatments without Bt than in those with Bt; thus, the use of Bt as a treatment provided significantly improved protection against corn earworm larvae compared to treatments without Bt.

Damage. Recorded damage ratings ranged between 0 and 2, meaning that until the last 2 harvest dates, larvae were rarely found further down than 2.5 cm (1 in.) from the tip of the ear. Most of the CEW were found in the silk above the ear. Part of this is due to that fact that in the early stages of ear growth, the ear is still elongating. Since larvae find ample silks to feed on, larvae tend not to move towards the developing ear.

The three main effects, time, oil, and Bt were significant (Table 3). Oil interacted with time to affect the damage rating per ear (Figure 13) while Bt and time did not interact significantly in either 2000 or 2001 (data from this mean separation is thus not shown). The oil treatment was more effective in suppressing larval damage on days 9, 12, 15, and 18 in both years. In 2001, the level of damage increased over time in the untreated ears compared to the oil treated ears.

Cone tip. In 2001 cone tip was observed and recorded (Table 4). Cone tip length measured in this year was longer in all treated ears compared to untreated ears. Ears receiving only Bt as a treatment had a mean cone tip length of 0.06 cm (0.02 in.) or 0.3% of the entire ear length, compared to 0.01% of the entire length in untreated ears. The oil treatment had a mean cone tip length of 1.24 cm (0.49 in.) or 6.5% of the ear, but the oil and Bt mixture recorded the highest reading of 1.69 cm (.67 in.) or 9.1 % of the ear. Clearly, oil had a greater effect on kernel development than Bt.

Marketable ears. Marketable ears were those that received a rating of 0 based on the damage scale used in this experiment. Cone tip was not used as a criterion for marketability. For both years, the number of marketable ears was highest in the plots treated with oil and oil plus Bt (Table 4). In comparison, Bt alone provided 88 and 83% marketable ears, while only 73 and 46% of the untreated ears were marketable in 2000 and 2001, respectively.

DISCUSSION

Untreated ears had more live CEW and higher levels of feeding damage than the other three treatment ears for all harvest days in both years. The number of CEW found per ear was lower when Bt was included in the treatment. The use of corn oil gave the lowest damage ratings on almost all harvest days in both years.

Treatments which contained oil had the highest number of marketable ears in both years, but also the highest percentage of underdeveloped kernels at the tip of the ear (6 to 9%). The oil and Bt treatments appeared to control CEW for at least 17 days, from silking through maturity. This treatment regime appears to be a promising alternative for growers to conventional pest management methods.

Although the actual number of live CEW found varied between the two years, the effects were similar. Though there were more live larvae found in year one than in year two, the untreated ears always had greater numbers of larvae than either of the treatments. Carruth (1942) and Hazzard (1997) found similar results, though only a single harvest was made at the milk stage of the ear in these experiments. Most CEW caterpillars and damage were found in the silks during the first three harvest days after treatment; this is most likely because the ears are short in the early stages of development and CEW feed on silks as well as kernels, leaving little reason for CEW to continue to move towards the developing ear. The level of damage increased over time as the ear grew and became more accessible to the larvae.

It appears that Bt is more effective at killing CEW than oil. One study in a petri dish showed that CEW was more likely to avoid areas with oil, but pass through areas with Bt (Pam Westgate, personal communication). It is not known whether this type of avoidance can occur within the silk channel or not. Visual observation of the silks treated with oil indicates that all silks are coated equally with oil throughout the husk, whereas when Bt is used alone (in a water solution) it sometimes beads up at the entrance to the silk channel. Since the mode of action of oil (we believe by asphyxiation) and Bt (stomach poison) are different, it should not be surprising that their effectiveness as treatments are somewhat different.

The oil appeared to have greater damage deterrence and for a longer period of time than Bt. As most corn takes 20 days or more to reach maturity once silks emerge, the longevity of treatment is an important factor. One farmer estimated that it took approximately 8 hours to oil one acre of corn (D. Kaplan, grower, personal communication). Organic growers, with few other options for controlling CEW in the silks, indicated that a single application is cost effective in that the increase in marketable ears compensates for the cost of the labor (S. Mong, Mass. grower, J. Manix, Vt. grower, personal communication).

Cone tip lengths were impacted in year 1 by the unusual cold and wet weather occurring in that growing season. In year 2, cone tip among the different treatments was more typical of what was observed in other studies (Carruth, 1942; Hazzard and Gault, 1993; Hazzard, 1994). Oiled ears had the highest percentage of cone tip on each ear. The silks at the tip of the ear (approximately the last ten rings of kernels from the tip) are the last to emerge and the tips are often still inside the silk channel when the oil is applied.

Typically, some portion of the tip is unfilled, even in untreated ears. Carruth (1942) suggested that 1.25 cm (0.5 in.) of cone tip was normal in an untreated ear, although modern varieties are expected to have complete fill all the way to the ear. Cone tip was not used as a criteria to determine marketability because consumer reaction to cone tip is also variable (Hazzard, personal communication). Growers who sell through direct markets such as farm stands and farmers’ markets in New England are able to explain cone tip to their customers. The explanation seems acceptable to consumers, especially those who prefer organically grown corn. Contact with consumers through the wholesale market, however, is not possible. Growers or retail packers who pre-package partially husked ears simply cut the tip off prior to packaging. However, further research to find ways to prevent the cone tip is worthwhile.

The data from this experiment appears to support the current recommendations from the University of Massachusetts for CEW control using direct silk application of oil and/or Bt (Hazzard, 1998; 2002). It also appears that the treatment is effective from silk day five through maturity and thus is a promising method for CEW control, especially for organic growers.

OBJECTIVE 3: EXPERIMENT 3

ABSTRACT

Field studies were conducted in 2001 to measure the physical effects of direct oil treatments on physiological development of sweet corn ears, Zea mays (L.), when oil was applied on 9 different days. The different treatment regimes included: 0.5 mL of corn oil applied directly to the silk channel of the ears using a Zea-later® on silk days 3 through 11; brown bags (to block pollination) placed over ears on silk days 3 to 11; bags placed over ears on day 0 and removed on day 3 to 11 with oil applied at this time; oil applied on day 3 through 11 with a bag placed over the ear on that same day; and no treatment. Silk day 1 is the first day when 50% or more of the corn has 2.5 cm of silk emerging from the ear. Results showed that only the treatment with a bag covering the ear from day 0 showed significant differences in ear development on most days compared to all other treatments. These ears showed significantly lower ear weight, kernel weight, and number of kernels when compared to all other treated and untreated ears. Among the other treatments, covering ears with a bag on day 3 through 11 showed very similar results to the use of the direct oil application but these results were not significantly different from the untreated ears. It appears that the most critical period for pollination is between day 0 and day 3 and supports other research, which recommends not using direct silk application prior to day 5. Also, it appears that corn oil does not completely block the pollination and fertilization process. The results suggest that the application of oil during the first three days of silking grossly inhibits the development of kernels, but after that, normal tip development occurs in increasing degrees.

Participation Summary

Education

Educational approach:
Presentations
  1. Bio-Intensive sweet corn production. VT Vegetable and Berry Growers Association Trade and Farm Show, Barre, MA. January 26, 2000; 40 attendees. (R. Hazzard)

    Management of Vegetable Insect Pests. NOFA-Mass Winter Conference, Hampshire College, Amherst, MA. January 29, 2000; 45 attendees. (R. Hazzard and D. Coldwell)

    Management of Vegetable Insect Pests. NOFA Summer Conference, Hampshire College, Amherst, MA. August 12, 2000; 50 attendees. (R. Hazzard)

    Management of sweet corn pests on organic farms. UMass Extension Twilight Meeting Series, Brookfield Farm, Amherst, MA. August 21, 2000. 54 people. (R. Hazzard)

    Sweet corn research update. SARE Project Report, Applefield Farm, Stow, MA. January, 2001. 15 attendees. (R. Hazzard and R. Cook)

    Management of sweet corn pests on organic farms. Univ. of Vermont Extension, Kestrel Farm,Westminster, VT. July 23, 2001. 20 attendees. (R. Hazzard)

    Organic pest management in sweet corn and other vegetable crops. CRAFT (CSA organization, eastern MA), Applefield Farm, Stow, MA. July 18, 2001. 20 attendees.

    Organic pest management in vegetables, including sweet corn. NOFA summer conference, Hampshire College, Amherst, MA. Aug. 7, 2001. 50 attendees. (R. Hazzard)

    Evaluation of Oil and Bt for corn earworm control in sweet corn (among other topics). UMass Research Farm, Univ. of Mass. Extension Field Day, South Deerfield, MA, August 21, 2001. 40 attendees.

    Gunning for earworm with the Zea-later. New England Vegetable and Berry Growers Assoc., New England Extension Systems, Sturbridge Host Hotel, Sturbridge, MA December 13, 2001. 100 attendees.(Jack Manix, Walker Farm, Dummerston, VT)

    Organic pest management in vegetables, including sweet corn. 2001 Northeast CSA Conference, Frost Valley Env. Ed. Center, Claryville, NY. 40 attendees. (R. Hazzard)

    Sweet corn research update. SARE Project Report, Applefield Farm, Stow, MA. January 17, 2002. 9 attendees. (R. Hazzard and P. Westgate)

    Growing organic sweet corn. NOFA winter conference, Barre, MA. January 26, 2002. 8 attendees. (R. Hazzard and Steve Mong)

    The Zea-later and organic sweet corn insect control. Northeast organic network field day, Kestrel Farm, Westminster, VT. August 2, 2002. 25 attendees. (R. Hazzard)

    Insect management: managing beneficial habitats, using organic pesticides. Working with Organic Farmers Conference. September 26, 2002.40 attendees. (R. Hazzard)

    Use of direct silk treatments with corn oil and Bacillus thuringeiensis for control of lepidopetran pests of sweet corn: timing effects on efficacy ear development. Annual Meeting of the Entomological Development Society of America, Orlando, FL. November 18, 2002. (R. Hazzard)

    Easy and difficult pests: tools for organic pest management. Organic Vegetable Production, Geneva, NY. January 16, 2003. 80 attendees. (R. Hazzard)

    Preventing insect damage in vegetable crops. NOFA/ MASS Winter conference, Barre, MA. January 25, 2003. 45 attendees. (R. Hazzard)

    Practical Production of Organic Sweet Corn: Growing a Healthy, Pest-Free Crop. Virginia Biological Farming Conference, Airfield 4H Conference Center, Wakefield, VA. January 31, 2003. 60 attendees. (R. Hazzard and P. Westgate)

Publications
  • Cook, R.; Carter, C.; Westgate, P.; and Hazzard, R. 2003. Direct Silk Applications of Corn Oil and Bacillus thuringiensis as a Barrier to Corn Earworm Larvae in Sweet Corn. Hort. Technology. In print, accepted for publication 12/02.

    Grubinger, V. and Hazzard, R.V. 2001. Farmers and their Ecological Sweet Corn Production Practices. An educational video on innovative production practices for sweet corn (40 min). Includes description of scouting corn, trapping corn earworm and European corn borer moths, using BT foliar sprays, and using the oil/Bt direct silk application with the Zea-later. Available for $15.00 postpaid from the UVM Center for Sustainable Agriculture. Contact via phone (802-656-5459) or email (susagcenter@zoo.uvm.edu). At the time of this report approximately 509 have distributed.

    Hazzard, R.V. 2001. Caterpillar Control in Organic Sweet Corn. In: The JSS Advantage, Johnny’s Selected Seeds. vol. 7:8-9. Distributed to approximately 10,000 clients on the Johnny’s mailing list.

    Hazzard, R. V. 2002. Insect management: managing beneficial habitats, using organic insecticides. In: Proceeding of Working with Organic Farmers: Enhancing Agency Involvement in the Northeast Conference. pgs. 71-76. Northeast SARE, University of Vermont Extension, Sept 26-27.

    Hazzard, R.V., editor. 2001. Zea-Later Owners Manual. Johnny’s Selected Seeds. 12 pgs. Delivered with purchase of Zea-later.

    Hazzard, R. and Pam Westgate. 2003. Bio-intensive Insect Management in Sweet Corn. UMass Extension Vegetable Program fact sheet #VEGSF 2-01. Updated and reprinted January 2003. Describes bio-intensive IPM system for sweet corn including trapping, scouting, identifying pests, using Bt foliar applications and using the oil/Bt direct silk treatments.

Publicity
  • Hazzard, Ruth.V. Caterpillar control in organic sweet corn. In: The JSS Advantage, Johnny’s Selected Seeds. vol. 7:8-9. Distributed to approximately 15,000 clients on the Johnny’s mailing list.

    Mattern, Vicki. The Sweet Season of Corn. Organic Gardening. July/ August 2001. 3pgs. Oil method discussed.

    Hazzard, Ruth, and Westgate, Pam. 2002. Sweet Corn all Summer!: Integrated systmen helps you identify and control caterpillar pests for perfect ears. Growing for Market 11(7):3-7.

    Diver, Steve; Kuepper, George; and Sullivan, Preston. Organic Sweet Corn Production: Horticultural Production Guide. ATTRA Publication September 2001. www.attra.ncat.org.

UMASS Extension Vegetable Program Website

UMASS Extension Vegetable Program Website http:///www.umassvegetable.org

Biointensive Insect Management in Sweet Corn
http://www.umassvegetable.org/soil_crop_pest_mgt/sweet_corn/biointensive_insect_management.html

Bio-Intensive Control of Caterpillars in Fresh Market Sweet Corn: Results of On-farm Trials, 2000, by Ruth Hazzard and Pam Westgate. Department of Entomology, University of Massachusetts.
http://www.umassvegetable.org/soil_crop_pest_mgt/sweet_corn/bio_intensive_control_caterpillars_2000.html

Integrated Caterpillar Control in Organic Sweet Corn: Results of On-farm Trials 1999, by Ruth V. Hazzard. http://www.umassvegetable.org/soil_crop_pest_mgt/sweet_corn/integrated_caterpillar_control_1999.html

Zea-later now available! Announcement of commercial availability of the Zealater and link to Johnny’s Selected Seeds website. (Summer 2001)

Project Outcomes

Impacts of Results/Outcomes

Three years of on-farm implementation of the bio-intensive control method have shown that caterpillar control using organic methods can be achieved on any farm, and with a tremendous diversity of growing conditions, pest pressure, farm labor and weed control. Factors affecting the results include scouting and timing of the foliar Bt and oil applications, weed control, variety of corn, size of stand and intensity and longevity of pressure. All growers experienced improvements in the number of clean, or marketable, corn ears. Results were greatly improved for the growers when they sprayed Bt to control the ECB caterpillars when damaging levels of ECB were present. Six out of the 8 growers achieved <80% clean corn in at least one of the oiled plantings while 4 growers achieved over 90% clean ears at least once.

There was a trend of increased improvement in control each year of the experiment. This can be attributed to improvements in the equipment and materials used, as well as increased understanding and comfort level on the part of the growers with the timing of the applications. The growers learned over the course of the experiment how to use trap capture data to time the oil treatments in silking corn. They also learned to oil the corn before the silks were too old –by the time they had dried out the damage had already occurred, but to not treat too early, as the oil will interfere with pollination. More on the important subject of timing is discussed in Objective 3.

Most of the plantings were subjected to threshold levels of ECB pressure or CEW flight during silk. Growers learned the importance of scouting the fields to determine when damaging levels of ECB or FAW are present and need to be controlled with foliar sprays or other available means. They also learned to monitor CEW moth flights to determine when to oil silking corn. During the trials, when CEW was not at threshold, usually ECB was. This allowed growers to see how much of the damage to their corn ears was from the ECB as opposed to the CEW. Further, the oil method did double duty at the tip as it did suppress the ECB caterpillar damage at the tip. The oil also resulted in a small significant decrease in the amount of side damage when foliar sprays were not used.

The cultivar of corn planted and the quality of weed control may be large contributing factors to the effectiveness of the oil applications, alongside timing. A tight-husked corn variety (Argent) planted at Wishing Stone Farm had much less damage in the oiled and non-oiled corn than the variety used in the experiment that had full, but looser husk coverage at the tip. A tight-husked variety is critical for adequate control, particularly in areas where CEW pressure is severe. The cultivars that do not have husk coverage over the tip expose the tip to caterpillars and are physically unable hold the oil as a barrier. Exposure to sunlight will also reduce the effectiveness of the added Bt.

It is also clear from working in weed-infested fields that large weeds in the corn fields prevent access to the ears for the oil applications. Not only does this make the task of oiling (zea-lating) very unpleasant, it also increases the application time, and thus the labor costs, and can result in inadequate control.
The health of the corn also seemed to affect the quality of control achieved through oiling. When plants and ears were stunted due to lack of water, or to wet and cold conditions, or to inadequate nutrition, the quality of ears produced was poor, and the corn earworm control compromised. A healthy corn stand of adequate size is necessary to insure good caterpillar control using the bio-intensive system.

It is important to realize that oil alone or sprays alone will not necessarily produce >80% clean corn. Depending upon the pest profile in any field, which can vary from week to week, sprays alone, oil alone, or both in the same week can be necessary, depending upon the stage of the corn. Controlling the ECB greatly enhances the ability of the oil method to keep the tips of the corn ears clean. While this project used foliar sprays of Bt, the actual method of ECB control can vary. There are now other materials that can be sprayed, such the organic formulation of spinosad (Entrust). The availability of Trichogramma ostriniae, parasitic wasps that feed on ECB eggs, also offers a new option for growers to control ECB that does not require spray equipment and may be equally, or more, effective as well as easier and less time-consuming to apply.

These on-farm trials demonstrate that the bio-intensive caterpillar control method is an effective and feasible way to commercially grow organic sweet corn free of caterpillar damage. The results on the farms with extremely high European corn borer show that separate means of controlling the ECB caterpillars is necessary. It became clear when working on farms that the plantings with the best weed control and healthiest corn were easier to oil, and were the most likely to have marketable corn. The results also demonstrate that when corn earworm pressure is extremely high achieving over 90% clean ears under these conditions may require other tactics, such as planting tight-husked cultivars. Further studies should examine which cultivars produce the best corn earworm control.

Economic Analysis

Farm Profile: APPLEFIELD FARM

Location: Stow, MA

Owners: Steve, Ray & Kristen Mong

Acres in Production: 40 plus greenhouses

Sweet corn acres: 8-9

Markets: Farmstand; Restaurant sales

Steve and Ray and Kristen Mong operate Applefield Farm, a 40-acre vegetable farm and roadside stand in Stow, MA, in the eastern part of the state. They do most of the farming themselves, and although they have hired summer help, they have had problems finding good workers. They grow mixed vegetables and raise flowers in their greenhouses. Most of their produce and flowers are sold at their farmstand, which is run by Kristen, some (5%) is sold to other farmstands, and they also sell to a restaurant or two. The farm is not organically certified, though they do follow the old Maine Organic Farming guidelines once the crops are in the ground, and they use IPM techniques.

Steve, who has been farming for 18 years, has grown sweet corn for 13 years. He grows it on 8 to 9 acres, generally in 6-7 plantings that are planted one every 10 days from April to late June. On Applefield farm sweet corn is the single largest revenue maker, with minimal handwork involved for the amount of time invested. At the start of this project Applefield charged 0.35¢ per ear of corn or $4.00/ dozen.

In Stow, they generally don’t have problems with caterpillars until late August, and then they can have damage in as much as 80-90% of their crop, though the average is 40-50%. When the corn has caterpillars their sales can go down by half. Steve says the biggest problem is with the new customers, as the “hard-core people will live with it.” When the corn was bad (60-70% feeding damage), they would leave a knife on the table for customers to cut off the tips of the ears. In late season corn their normal practice was to ignore the caterpillars, and hope that the customers would too. Unfortunately, they did not, and sales dropped. To prevent a loss in sales when their own corn is really infested with caterpillars, Applefield will sometimes buy clean corn from other growers.

The Mongs found that when sweet corn has up to 10% caterpillar damage it is not considered bad, though when caterpillars are in 20% of the corn they start getting complaints. At this point they visually check all corn for borer and discard it at the time of picking. If damage is consistently greater than 20%, sales will be reduced, and they will offer some corn at retail that they have already husked. This is what they had to do during the growing season of 2002, which was wet and cold early, and then very hot and dry- a challenging sweet corn growing climate. The Mongs were so busy moving water pipes for irrigation that they did not have time to treat the ears despite the heavy corn earworm pressure. They were able to make the best of it, however, charging 0.60¢ per ear for husked ears with the tips cut off, and 0.45¢ per ear for ears with the husk and caterpillars.

In the past Steve used Bt foliar sprays to control the first generation European corn borer caterpillars, but not the second generation in the later corn. It is in the later plantings that corn earworm is generally a problem in their area. Applefield Farm was one of the first farms to try the oil method, and helped to shape the research that was subsequently conducted. They had been using the oil / Bt system for a number of years before the start of this project, and were not satisfied with the method when the time and effort failed to control the damage. Our goal during the project was to work with the growers on effectively timing the application. While the bio-intensive system involves foliar Bt sprays to control the corn borer when necessary, as well as the oil sprays, Steve was hesitant to spray his later plantings, and did not apply foliar sprays at all during the 2000 growing season. His results, accordingly, were not as good as expected for that year. As Steve stated, the control was “much better than nothing but would like even better control for the effort involved.” The final year of the project, 2001, he did make foliar applications of Bt, and was pleased with the increase in European corn borer control that he achieved.

The Mongs have found that they are able to sell more corn when they control the corn earworm with the oil method, and enjoy the satisfied, happy faces of the customers. Steve also finds that actually applying the oil to the corn ears is peaceful because you can’t rush the job. With good control, Applefield Farm is able to extend their sweet corn selling season. They have better customer retention and get rid of the bad publicity. They intend to continue to use the oil / Bt method after the project ends because “it’s effective enough to keep sales relatively steady through the season”.

WALKER FARM

Location: East Dummerston, VT

Owners: Jack & Karen Walker

Acres in Production: 30 plus greenhouses

Sweet corn acres: 8-9

Markets: Farmstand

Walker Farm, in East Dummerston, VT, is a 65 acre farm, with 30 acres in production, and farm-stand that sells diversified vegetables (from artichokes to zucchini), cut flowers and herbs, and potted flowers, herbs and bedding plants. Jack runs the farming operation with his daughter, Kristen, while his wife Karen runs the farm-stand. They have split farm organic certification, where the vegetables are certified organic, and the flowers are not. The farmstand emphasizes high quality in all of its produce and flowers.

Jack has been growing sweet corn for 25 years. He grows up to 10 acres in 6-7 plantings between May 1 and July 4 (for harvests from the end of July to the end of September). Sweet corn is very important to the farm-stand, its presence being essential for people to stop at the stand in the mid to late season. Also, Jack says they can’t get it as good as they can grow it, stating that organic sweet corn, with the husk appearance, and flavor of the SE, are all obtainable on their farm. When they have a good yield they can make money on the corn, directly. The Walkers have increased the price of corn to 0.40¢ per ear or $4.50/dozen throughout the season. In the past they charged $4.80/dozen early and reduced it to $3.60/dozen later in the season.

On this farm in southern VT, the CEW and ECB pressure increases through the season. They can have anywhere from 20-80% infested ears by the end of September. The customers, however, including the ones who specifically want organic food, want clean corn. When the corn is heavily damaged, the customers don’t come back and, therefore, don’t pick up other stuff too. Overall sales will decrease by 10-15% when the corn is heavily damaged by caterpillars. To avoid this Jack will buy and resell corn from other growers.

When the corn has caterpillars in it, the customers react. Up to 10% wormy the farm can sell corn as is, as the customer response is usually OK. When it is 20% wormy, the customers “commence gagging” so the Walkers examine every ear. Greater then 20% infested and the customers “start throwing cobs at the farmer,” so to prevent injury they cull the wormy ears or chop the tops off, cell-o-wrap the ears and sell them for more.

Because of his inland northerly location CEW is not a problem every year, though it does make appearances. Over the course of the experiment no more than 3 CEW moths per night were found in the traps (the threshold for commencing sprays in conventional corn is 0.29 moths per night). Despite the low number, significant levels of damage were found. In the block that was in silk during this moth flight, approximately 37% of corn ears out of 100 were damaged and over 20 caterpillars found in the ears. This compares to an average of 15 moths per night resulting in 80+ caterpillars and tip damage to 70% of the 100 ears at Applefield Farm (see Figure or Table).

Jack sprays Bt on the corn foliage to control ECB, but until he learned of the oil method, he had no options for CEW control. Since a few years before the start of this project he has been involved in developing the direct oil method, and has been using it as needed. He has also purchased his own Heliothis net traps for monitoring the moth populations and has one of his seasonal employees check the traps regularly. This is particularly important in a situation such as his, where it may not be necessary to oil the crop.

The oil / Bt system worked well for Jack. He has successfully incorporated the IPM monitoring of moths and caterpillars. He also has a boom sprayer and is comfortable spraying Bt to control the European corn borer. As he has a large summer crew, the labor to apply the oil method is not a problem for him as it is easily absorbed into the overall list of tasks. Indeed, he finds that “younger workers would rather oil than pick beans” and that Zea-lating is one of the more desirable jobs on the farm. Jack was happy with the control achieved, as he had a good percentage of clean and marketable corn. In every block of corn that he planted for the trials he had at least 80% control, usually greater than 90%.

Achieving good control was a bit more challenging for Jack in the 2002 growing season where he reported catching greater than 70 CEW moths per night. He found that the oil applications definitely paid off this season as he only had to apply once, while the conventional growers in his area were spraying every 2 days. He figures that it is cheaper to spray than to Zea-late if you are only spraying twice, but if you have to spray 3 or more times than you are ahead of the game. Furthermore, Jack claims that in the heavy CEW season of 2002, the chemical guys couldn’t control the corn earworms. One of his alternative suppliers is a conventional sweet corn grower who ended up with caterpillars in every ear despite spraying on a 2-day schedule. Jack, on the other hand, had some blocks of 90% clean corn in the blocks that were oiled properly, and 70-80% in the others (his estimate). He had two employees oiling this year and was unhappy with the quality and consistency of the application of one of these workers. Aside from finding a responsible person for the oil application, the timing of the application is his most important concern.

Overall, the oil / Bt system project, has had a large impact on Jack’s farming operation. It has allowed him to grow caterpillar-free organic sweet corn. He “can look customers in the eye and they don’t have to look the worm in the eye.” For him, the oil method “works well, we’re happy.”

BROOKFIELD FARM

Location: Amherst, MA

Farmer: Dan Kaplan

Acres in Production: 18

Sweet corn acres: 4

Markets: Community Supported Agriculture (CSA)

Brookfield Farm is a community supported farm (CSA) with two customer bases. One group of members come to the farm in Amherst, MA, while another group is from Boston, and has their vegetables delivered to their area from the farm in Amherst. Dan Kaplan runs the farm and has been farming for 13 years. They have 18 acres in vegetable production, 40 acres in hay, and 15 acres in pasture for the cows. While the farm is not organically certified, all of their practices are organic. They use IPM scouting and monitoring techniques, although they do not spray. Dan has been growing sweet corn for 10 years and has grown up to 4 acres in 7 plantings ranging from May 11 until July 4. He views corn as a staple crop that customers use as a marker for the quality of the farm.

Corn earworm and ECB pressure on the farm is generally low in July, increases in August, and is a lot higher in September. What the customers expect in terms of clean corn varies. Most want moderately clean corn, but will tolerate up to 10% damage. Since Brookfield is a CSA, they do not charge for the corn specifically, nor do they have direct market losses due to damaged corn.

Dan is a big supporter of the oil/Bt caterpillar control system, and plans to continue to use it after the project ends: “I think it provides excellent control which [meets] our market needs.” The CSA customers react the same as farmstand customers at other farms to caterpillars in the corn. In particular, when the corn is >20% damaged, the reactions are very negative and his only option is to plow the crop under. When the corn is 10-20% caterpillar damaged he may cut the tips off of the ear. Only when the corn is <5% damaged are the caterpillars not a problem. Because Brookfield Farm is a CSA, clean corn does not affect the economics in a direct fashion (it doesn’t draw people in, for example) but Dan does report higher customer satisfaction when he can provide caterpillar-free sweet corn.

In the past Dan has plowed in the crop when infestations were very high. He uses crop rotation to reduce the impact of European corn borer. For the few years before this project Dan would call on his local Extension agent when caterpillar pressure was high. His agent, being the woman (Hazzard) who has been working on this project for over 10 years, would tell him to spray Bt and oil the silks. When he did spray and oil he would have good control (95%).

Dan did not spray for ECB during 2000 because he felt the moth levels were not high enough and he prefers not to spray. Interestingly, when we scouted the field it was at threshold, but we found few ECB in the corn at harvest. This may indicate that he has a healthy population of insect predators. He felt the system worked well despite technical difficulties with the Zea-later prototype. Dan wanted to oil all of his corn when CEW was present, but he was a good collaborator and left us an untreated block. He says good control of the caterpillar pests results in him having pride in the product, and in general higher customer satisfaction.

Dan is still working on weed control in his corn, and uses several cultivations from pre-emergence through whorl stage. Otherwise, while he feels that the costs of the oil/Bt method need to be looked at, particularly of the labor involved in the oil/ Bt system, he has a large crew and treating the corn silks with oil is one of many tasks on the farm that gets delegated to one or more of the farm crew when needed.

Dan and his crew were satisfied with the oil/Bt system in the summer of 2000, achieving “excellent control.” Dan was able to easily train an employee who did a very thorough job. His two main concerns were 1) having 2 Zea-laters so that “I could get people working together and not getting ‘lost’ in the field.” and 2) being worried that they wouldn’t get the scouting right after the program ends. The most important things Dan and his field hands think that a grower using the system for the first time needs to know are “when to scout, how to scout” and “what to mix, how to apply”.

In the hot and dry 2002 season Dan did not oil any corn because there was no moth pressure when the one planting of corn that survived the birds and drought was in silk; however, he plans to continue oiling his silking corn when it is subject to caterpillar pressure.

THE UPPER FORTY

Location: Cromwell, CT

Owners: Kathy, Andy and Ben Caruso

Acres in Production: 22

Sweet corn acres: <1

Markets: CSA; Farmer’s Market; Farmstand

The Upper Forty Farm in Cromwell, CT is a NOFA certified organic farm run by Katherine, Andy (son) and Ben Caruso. For the past 15 years they have grown herbs, flowers and vegetables (specializing in heirloom varieties) for retail at a farmers’ market, their farmstand, and through their CSA. They had 22 acres in production in 1999. Both Andy and Ben work outside of the home full time, farming at home in the evening and on the weekends. Due to time and previous space constraints, they had not grown corn on their farm until this trial, though there is a demand for organic corn at the farmers’ markets and they were interested in it as a crop for the possible income and to have another organic crop to sell. They do not want to sell corn that has caterpillars in it. This farm is about 45 minutes from the coast of CT, and receives medium to high levels of corn earworm pressure from July through September. Their market demands clean corn, so the Carusos will sort through the corn and cut off the tips that have caterpillars or toss them. At the farmers’ markets they initially charged $4 / dozen ears of corn throughout the season; however, they have increased their price to 0.50¢ an ear, or $6.00 a dozen. They expect to sell at this price because the farmers’ market they sell at is in an affluent section of central CT.

The Carusos found that the oil/ Bt insect control system worked well for them when they were able to grow corn. Unfortunately, in 2000 they were unable to produce marketable corn due to wet and cold conditions, raccoons and poor soil. They also lost their 2002 crop to raccoons. Once this animal problem is controlled, they believe that they will be able to grow marketable corn.

One issue that was raised on this farm is the economy of scale. The Carusos planted small blocks of corn because they have limited labor, yet when raccoons came they were able to decimate the small planting. The Carusos are also less likely to invest in a sprayer for the European corn borer Bt spray applications. A Trichogramma ostriniae release would probably be the best way for them to control ECB. As Kathy pointed out, you need to grow a lot of corn to make money at it.

Nevertheless, despite these difficulties they want to grow corn to supply their CSA customers and the people who go to their markets to buy tomatoes and corn. They will squeeze the corn growing into their daily operation for one more year and see if they get a crop. If not, they will discontinue growing it. Andy notes that the person making the oil applications has to be experienced, and that the timing of the application is “everything.” When asked if they planned to use the Zea-later in the future, Kathy responded “Oh yes, definitely.” They will continue to grow corn and use the oil/ Bt method, as that is their only hope for achieving marketable corn with the corn earworm pressure they experience.

WISHING STONE FARM

Location: Little Compton, RI

Owner: Skip Paul

Acres in Production: 16

Sweet corn acres: 3 (now zero)

Markets: CSA; Farmer’s Market; Wholesale

Wishing Stone Farm is on the coast of Rhode Island and run by Skip Paul, who has been farming for 16 years. He grows various vegetables for the supermarket wholesale market (50-60%) and the rest for farmer’s market and some farmstand sales on approximately 16 acres of land in production. Wishing Stone Farm is organically certified, which is important for the supermarket sales. Over the last three years he has taken a break from farmstand marketing and is slowly buying more machines to replace his labor, as he has had difficulty finding employees. In the next few years he intends to work on expanding his growing season, continuing with more greenhouse work.

Skip has been growing corn on and off for 15 years. The maximum amount of acreage in corn that he has grown in the last five years is 3 acres, which is planted in one or two early plantings. Corn has become less important to Skip in his farming operation. Although it was important at the farmstand, he has since discontinued operating the stand. Also, in contrast to the Caruso’s experience in CT, Skip has experienced a low demand for the corn at the farmer’s market. His other market, wholesale organic grocery stores, demands greater than 90% clean corn. He is in an extremely high corn earworm pressure belt, however, and has been unable to produce corn that clean. These problems, coupled with difficulties finding reliable help and land availability problems, have induced Skip to discontinue growing sweet corn.

Being on the Southern New England coast, Wishing Stone Farm has tremendous corn earworm pressure. There is also high ECB pressure on the farm, as well. When he was growing corn he would not grow it for September harvest because the pressure is so intense at the end of the season that every ear would be damaged, and the pressure is only a bit less in August and July. His markets had similar reactions to caterpillar-filled sweet corn than that of some of the other growers: 5% ears with caterpillars is ok, 10% is maybe and over that- “no way.” When over 20% of ears are damaged: customers “never buy your corn again this year.” So, he would leave 5% wormy corn alone, cull the 10%, chop the 20% and plows anything greater than that into the ground. Unfortunately, the wholesale market expects and requires clean corn, for which he gets only $3.50/ dozen.

In the past, Skip grew sweet corn conventionally and got “OK” control, though even then the pressure was sometimes too great and he would have corn that was too infested with caterpillars to sell. In 1999, the trial year of the project, the oil/Bt system did not work well for Skip. He had problems with the Zea-later applicator prototype, the dry Bt and oil did not mix well, and he had poor seed germination. From the outset, Skip maintained that due to the previously mentioned problems, even if he was able to get good control with this method, he did not think it would change his operation that much as he is not investing much into the sweet corn production. Only if he were able to get a premium price (from Bread and Circus) such as $6-7, would he reconsider; however, he has not found a great demand for organic sweet corn.

Skip was satisfied with the control that he achieved using the oil/ Bt system in the second year of the project. A key improvement for him was the addition of an emulsifier that kept the Bt in suspension in the oil. He would like to see a longer tip on the applicator. Skip was not satisfied with the help he had making the applications. One of his concerns is that he is not sure that he can trust someone to do an accurate job: “[I] don’t know if I can trust someone to take a large acreage and keep the discipline to be accurate.” For Skip, there are too many risks and not enough return to grow corn.

As for how he feels about the bio-intensive control method, he states “Depending on bug pressure, it can be a very successful solution.” Skip has the following recommendations for growers using this method:
1-Have a clear understanding of critical time of application parameters.
2-Have your best man do it [Zea-late] and not some first year teenager who wants a farm experience!
3-Use part two [foliar Bt applications for ECB] as well and spray Bt on exterior of ears at least twice.
4-Keep weeds under control.
To this we would add that sprays should only be done when scouting indicates above-threshold levels of damage or moths.

As discussed in the experimental results section, weed control was a problem on this farm due to the distant location of the field from the rest of the farm and the particular weeds that were there, which were large enough to create access barriers to the corn for the farm workers doing the oil applications. We learned a tremendous amount by working with the pest conditions on Skip’s farm.

COOLWATER FARM (now FullBloom Market Garden, LLC)

Location: Whately, MA

Owner: Doug Coldwell

Acres in Production: 38

Sweet corn acres: 4.5

Markets: wholesale

Doug Coldwell has been vegetable farming for about 8 years. As the owner of Coolwater Farm he was growing organically certified cucurbits, bell peppers, beans and sweet corn for the wholesale market on 38 acres of leased land in Western Massachusetts at the outset of the project. He is now a partner of Full Bloom Market Garden LLC. Doug did not grow corn before this project and decided in the final year that he could not make enough money on sweet corn to warrant planting any more.

During the project he grew 4.5 acres of corn in 6 or 7 different plantings. He began sweet corn production with seeds for transplant in early April and planted directly in the field up to mid-June. He was initially interested in growing sweet corn because it is a good rotation crop, would make his co-op more attractive to buyers, and because he thought it could become profitable.

Previously, Doug worked on a farm that grew sweet corn. To achieve control of the caterpillar pests there, they used frequent applications of conventional insecticides. While they achieved the required damage levels of below 5-10% in July and August, he says that September was generally a disaster. At the farmstand, when the corn was filled with caterpillars, customers would open the ears and leave. In his own farming operation Doug had difficulty with the uniformity of his corn stands (a common compliant), and with the caterpillar pests. The caterpillar pressure on his farm, as in his previous experience, was light in July. By August the corn generally needed to be treated to control the corn earworm and European corn borer, and late season corn continued to be “pretty much disaster.” The wholesale market requires corn that is >90% free of caterpillars. He was being paid $3.00 / dozen and had average yields (“not great”) of 120 bags/acre.

While he was participating in the project Doug said that the only way to get decent certified organic corn is to use the oil / Bt system, and that he liked the control achieved when it was applied at the right stage of silk growth. He would prefer to have more than one Zea-later on the farm for applications, with possibly up to four individuals working at the same time. Doug also found that the biggest challenge was timing the oil application. Other growers have echoed this sentiment.

In the 2000 season, which was wet and cold, Doug ended up growing less than one acre of corn due to poor germination from cold and wet soil. While he was happy with the amount of caterpillar control that he had using the oil / Bt system, he qualified that by saying the pressure on this planting was low to begin with. He did not feel like he had grown enough corn to evaluate the system, but he did state “I think the labor is reasonable if control is good enough to reduce damage to less than 10% all the time.”

When asked if he was planning on continuing to use the system after the project ended he said no, stating that it is “not economically viable to grow sweet corn for wholesale….I’m not sure corn- even with 100% clean ears- is a viable crop on my farm. $300/A land rent $700/A fertilizer- expensive hand / mechanical weed control and hand oil application. With a lukewarm and suspicious (of insects) wholesale climate, and $3.00/dozen price-
I’m not sure it could add up even with good seed germ etc.” We do not have data from Doug for the 2001 growing season, as he had by they determined that the costs of production were too high for him to grow sweet corn.

GORANSON FARM

Location: Dresden, ME

Owners: Rob & Jan Johanson

Acres in Production: 54

Sweet corn acres: 5

Markets: wholesale, farmers’ market, farmstand, CSA

Jan and Rob Johanson are second generation farmers and have been operating Goranson Farm in Dresden, Maine since 1986. They grow mixed vegetables and livestock (meat birds, pigs) on a 153-acre farm with 54 acres in production. The 2002 season was the first season in which they produced and sold organically certified vegetables on 18 acres of the farm. By 2004 all of their 54 acres of vegetable production will be certified. A combination of marketing techniques is employed to distribute their food to customers: 10% is sold wholesale, 35% is distributed through a CSA (175 members), while the rest is sold at their roadside stand and farmers’ markets. They farm using integrated pest management techniques (IPM) where available: corn has been grown using IPM with the help of the University of Maine Cooperative Extension Sweet Corn IPM project, which provides IPM scouts that check traps and scout fields free of charge. Goranson Farm is transitioning to certified organic because they philosophically like to practice organic techniques for general safety and health, and because they are interested gaining access to those markets. Corn and potatoes have been their last barriers to the organic transition.

Rob and Jan have been growing about 5 acres of corn consistently for 17 years. Corn is planted under row cover at the end of April and then weekly throughout June. They view corn as their ‘loss leader’ as it brings people to the farmstand and their spot at the farmer’s market. They do make some money on it, charging from $4.50/ dozen early to $3.50/ dozen later in the season, with yields of 700-800 dozen/acre. In 2002 they charged $3.75/ dozen for their organic corn. They are gradually raising the price of their main season corn by $0.25/dozen per year over a couple of years. The increase in price is not to offset the cost of oiling the corn, but to the increase in grading and culling that he is doing in his organic corn, as the organic corn still does not look the same as his conventional corn, and he is dedicated to keeping the quality high.

Because Goranson Farm is <5 miles from the Maine coast caterpillars are a problem on their farm. Sometimes they get corn earworm moths in July. By September they generally have the highest trap counts in the state. While their customers will tolerate a lot, Rob says he "can't expect to get away with it all of the time." If a bad storm comes up the coast, bringing high numbers of CEW moths with it, they have to explain to their customers why there are so many caterpillars. They are operating under the same acceptance standards as the other growers in the project- when the corn has caterpillars in up to 5% of the ears there is no problem, the market says ok, at 10% the market is less accepting, and when 20% or more of the corn has caterpillar damage it is not acceptable and the corn must be trimmed or fed to the pigs.

Rob and Jan have been participating in the last three years of trials on the use of the oil method and the development of the Zea-later. Greater than 90% control is required for their wholesale market (10%), yet in the 2000 growing season they averaged 81%. While he would prefer better control, Rob believes that better timing of the oil application will increase their percentage of clean corn. He also plans to use the newly available organic formulation of spinosad (Entrust), as it is supposed to work well to control fall armyworm, which can cause a significant amount of damage in his corn. Rob thinks that he can get up to 95% clean ears in his corn: he was happy with his results in 2002 (after the project had ended), but had a set back with fall armyworm in September, when he no longer had scouting support.

During the course of the project one of his biggest concerns was determining when to treat the corn ears with oil, though now he is “less concerned about the window for the oil treatment after seeing our [research] results” (Objective 3). Another concern was the amount of time it took to do the application. He would prefer to pay an employee for one to two days of oiling just over one acre of corn, however, than to spend the three hours it takes him to set up the sprayer, spray the corn and clean the sprayer. He likes the fact that any responsible person on the farm can make the applications.

This bio-intensive control system has had a tremendous impact on this farm that is transitioning from conventional to organic. Corn was one of the last two crops on his farm to go into organic production due to the barrier of organic insect control. Now that he has the oil method and knows how and when to oil for CEW and spray for ECB and FAW he can grow organic sweet corn.

KESTREL FARM

Location: Westminster, VT

Owners: Tom Harlow

Acres in Production: 50

Sweet corn acres: 10-15

Markets: wholesale

Tom Harlow farms mixed vegetables on 50 acres of land in Westminster, VT, that was once his uncle’s farm, but that he now owns. Tom has been farming for 27 years, 14 of which he has been growing sweet corn. Tom grows certified organic vegetables for the wholesale market (supermarkets, 80%) and farmstands (20%).

Sweet corn is a cash crop on Kestrel Farm. While the per-acre growth is not great, he manages to sell all of it. He also uses it for help in weed control and soil management. He has grown as much as 15 acres in approximately 10 plantings from April through July. Tom produces between 200-250 bushels of corn / acre. He sells it at $10-12 bu/ or $2.40/dz to the local wholesale market and at $16 / bu to the local food co-op. He has figured that it costs him $7 / bushel in production costs and $1.25/ bu for marketing.

Tom’s farm experiences heavy ECB infestations in July and September, while the CEW pressure varies but can be really high in September. While the retail market, which is only 20% of his market, will accept slightly more infested corn, the wholesale market that comprises 80% of his market demands >90% clean corn. When the caterpillar pressure is great, he can loose his wholesale market, an 80% loss. He reports reactions to the caterpillars to be the same as the other growers. When the corn is 5% wormy he does nothing and the customers don’t say anything. When it is at 10% there is some negative reaction, so he provides verbal warnings. At 20% and higher, the supermarkets won’t buy the corn and local sales slow down, so his response is to cull the corn.

In the past Tom controlled ECB with a mist blower and did nothing to control the corn earworm. Tom found that the oil method was easier and faster than he thought it would be. He was not, however, pleased with the variety of sweet corn grown for the trial or the material used during the 1999 season (Bt powder did not stay in suspension, solved in 2000 with addition of an emulsifier). At the beginning of the project Tom stated that if he was able to achieve good insect control with the oil/Bt method he would be inclined to grow more corn, especially in late August and September, when he usually cuts back on the planting size.

Tom was satisfied with the equipment and materials needed for the oil/Bt application method. Tom was not satisfied with the control achieved in the 2000 growing season (72% clean treated vs. 56% untreated). Most of the pressure and damage at Kestrel farm is from ECB rather than CEW. Tom was pleased with the results in 2001, as there was no corn earworm pressure and the 2 foliar sprays plus the oil treatment controlled the ECB. He plans on using the bio intensive control system after the trial is over: “I see fair to good control. With practice I expect to see improvement.” Also, the improvement he saw in the amount of ECB damage was related to his adding an additional foliar spray during early silk. In the past Tom had only sprayed during tassel stage, but the ECB pressure continues after that on his farm, so the early silk spray had an impact. At the end of the project he stated that he now is “more confident planting late corn for market.”

Tom thinks growers should know the following to use this method successfully:
1-Monitor with traps
2-Foliar Bt spray at silk during heavy [ECB] pest concentrations
3-Don’t oil too early
Among the above list, Tom learned through his participation in this project that “oil for CEW and ECB works,” and ”weedy corn takes longer to oil.”
This past year (2002) Tom used the Zea-later to control the CEW and Trichogramma ostriniae wasps for ECB control and reported <10% damage to his sweet corn despite damaging levels of CEW pressure. He also is now getting $3.00/dozen for his wholesale organic corn.

SUMMARY/ BENEFITS & COSTS

Labor: cost, availability & quality. The high cost of labor was frequently cited as a disadvantage of the oil method due to the labor-intensive nature of the applications. Zea-lating one acre of corn can take 8 hours, and at $7 – $10 per hour it can cost from $49 to $70 in labor costs to treat one acre (for cost comparisons between bio-intensive system and conventional see Appendix B). For those who do most of the farming themselves and have few field employees, the biggest drawback to the Zea-later method is the time it takes for them to make the applications. Not all of the growers who were making the applications themselves felt as strongly about the time they were spending in the corn: one grower does the applications himself and finds the time in the corn relaxing and meditative.

Yet one of the advantages of the oil method over conventional field sprays for corn earworm is that it can be done by the farm crew- the “unskilled labor.” For those growers who have a field crew, the oiling method reduces the time they have to spend on the tractor applying sprays, and frees them up to do other important jobs around the farm. This is a significant savings in time for the grower who would otherwise be applying conventional sprays 3-6 times per planting of corn to control the corn earworm. Add this up to the 3 hours that Rob Johanson estimated he spends loading, spraying and cleaning the spray equipment for each spray, and the time savings can be significant, especially on a small to medium farm with a lot of small plantings of corn. According to those numbers, the cost analysis in Appendix C underestimates the time it takes to apply conventional CEW sprays.

The growers who had more field help, though concerned about the labor cost, were less concerned about the time it took to oil the corn, saying it was just one of many jobs about the farm that they would assign to the farm crew. Some of the growers expressed concern about the quality of the labor that they had access to, and were concerned about entrusting the value of their crop to the quality of applications. The key here, as one grower stated, is to have a detail-oriented employee do the job so they notice if something is not quite right, such as less oil being delivered because the device is clogged. As for any job around the farm, you should know the strengths of your employees and train them properly. If you as a grower are concerned about the method being done well, then having good to great weed control in the field will go a long way towards ensuring that every ear will be treated. You also have control over the process because you determine when to treat the corn based on field scouting and trap captures.
The bottom line for growers who wish to grow fresh market sweet corn organically, as one grower put it, is to either use the labor up front by Zea-lating, or later by cutting off the corn ear tips.

Threshold of infestation vs. cost of labor. The wholesale grower, in VT, where CEW pressure is not as intense as at other sites closer to the shore, says that if the pressure was higher for him, then he would need to recover the cost of treating all of his corn with oil, or he would have to cut back and consider not growing sweet corn, which is what we saw happen with Doug and Skip, growers who were selling their corn through the wholesale market. If the demand for organic sweet corn goes up, then wholesale purchasers will have to either put up with caterpillars in the corn or raise the prices they are willing to pay if they want to find suppliers in areas where corn earworm are perpetually in abundance.

Uniformity of corn stand. Given the dangers of oiling corn too early (as discussed in Objective 3 of this project) it is difficult to treat the corn when the stand is very uneven in age, which is common. We discussed this at the grower meetings, and although it was a concern, the discussion revolved around how to deal with that problem. In particularly uneven stands, one option is to go through the field twice, still only treating each ear once, but waiting a few days for the younger ears to grow some more before treating them.

Equipment. The Zea-later, retailing for just under $225 is relatively inexpensive compared to a sprayer. However, the bio-intensive control method tested in these trials requires the use of sprayers to control ECB and FAW, when present, as well as the use of the Zea-later for CEW control. There are alternatives to huge expensive sprayers. One is the backpack sprayer, which comes in varying sizes and costs and is relatively easy to load and use. Another alternative that would eliminate the need for spraying altogether, assuming no FAW infestation, is the use of the Trichogramma ostriniae wasp for bio-control of ECB combined with the Zea-later for CEW control.

Timing. As the oil method has been developed, the timing of the applications has remained a question. The experiments in Objective 3 of this project addressed these questions. The results of these experiments, discussed below, were presented to the growers during our winter meetings, and alleviated many of their concerns.

Other factors. It is important to keep in mind that growing a crop organically is more than substituting organic pesticides for conventional ones: it is a crop management system in which pesticides are only once piece of growing a healthy, marketable crop. If you have poor weed control, you may have poor caterpillar control using the Zea-later. Likewise, fertility or water problems in the crop can produce physiologically challenged ears that respond poorly to the oil treatment. As we have seen on these farms, using oil to help control the CEW depends upon the whole system of management: factors ranging from weed control, nutrient and water management, and corn variety all play an important role in supporting and improving the effectiveness of the oil method.

Farmer Adoption

Of the eight growers who participated in the on-farm trials, six plan to continue using the bio-intensive system of caterpillar control. For the grower who was transitioning to organic, sweet corn had previously been a barrier to full farm organic certification. Due to his results with the oil method, he now feels he can successfully grow organic sweet corn.

The two farmers who have decided not to adopt this method have opted to discontinue growing corn for economic reasons. Both growers were selling on the wholesale market and not getting a high enough price to make the crop worthwhile to grow. Both growers rented land to grow corn. One grower was not growing sweet corn on his farm at the start of the project and decided a couple of years into it that the costs in land rental, fertility, and management were too high. The other grower had land issues and did not find a demand for organic sweet corn in his area.

Approximately 125 growers have purchased the Zea-later oil application device from Johnny’s Selected Seeds since it became commercially available in the summer of 2001.

Areas needing additional study

There is limited data indicating that the oil treatment works better on varieties with good husk coverage; however, variety trials have not been conducted. Information on the effectiveness of the oil treatment on different varieties of sweet corn would be useful to growers.

Further work on the timing of oil applications in high corn earworm pressure areas is needed. All of the farms in this study were in locations that had corn earworm migrating into the area at some point in the later part of the season. It was difficult to achieve great control of corn earworm in the locations that have perennially very high pressure. In southern areas with intense season-long pressure, additions or alterations of the oil method may be necessary to make sweet corn more profitable in these areas.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.