The objective of this project was to reduce grower dependence on chlorpyrifos use to manage an important pest, the cabbage maggot (CM; Delia radicum L.; Diptera: Anthomyiidae). A “toolbox” of integrated management strategies was developed, which includes: monitoring (flight, eggs, and damage); degree-day modeling of flight and emergence; spatial management (a regional grower-friendly GIS mapping and rotation plan); cultivation techniques; row cover and exclusion fence usage, planting and harvesting schedules, and alternative chemistries and application methods for control of CM. A tool for researchers and growers is being refined to evaluate program impact and grower IPM adoption over time called the PEST Plan.
The main supporting objectives of this research project to reduce chlorpyrifos use and control cabbage maggots were to:
Define seasonal impact of cabbage maggots in western Oregon.
Research, evaluate, and implement IPM strategies in cruciferous crop production.
Build collaboration between growers, researchers, and extension personnel.
Inspire grower IPM interest and adoption of pest management tools for control of the cabbage maggot.
Establish a harvest assessment of CM damage
Install “no-spray” plots in growers fields
Develop a degree-day model for predicting seasonal flight
Implement a viable monitoring system (flight, eggs, damage)
Identify alternative chemistries and application techniques
Evaluate cultivation practices to reduce overwintering CM populations
Evaluate the use of row covers for managing CM in root crop production
Develop a GIS-IPM tool to assist growers in spatial CM management
Transfer technology to VegNet, Ag consultants, Brassica growers
Hold workshops (e.g., GIS-IPM tools, degree-day modeling, use of monitoring techniques) and present information at scientific meetings
Create a grower monitoring kit
One-on-one grower interaction in field
Development of “the PEST Plan” to assess progress and grower adoption of IPM practices
Brassica vegetable growers in the northern Willamette Valley, Oregon are highly dependent on scheduled insecticide treatments of chlorpyrifos (Lorsban; organophosphate) for control of the cabbage maggot, Delia radicum (L.). In Oregon, Brassica crops (fresh market, processed, and seed) are grown commercially on over 20,000 acres and valued in excess of $20 million annually. Females lay eggs around the base of domesticated and wild cruciferous plants, eggs hatch, and larvae feed directly on roots resulting in severe reductions in crop quality and yield. In root crops such as rutabaga and turnip, larvae can render the crop unmarketable if more than slight feeding damage is evident at harvest. The pest is proving to be a major and devastating problem in the Valley. Root damage caused by cabbage maggots has increased since 2001 (Fig. 1), reinforcing the need for an IPM strategy. No monitoring or pest phenology tools have existed for cabbage maggot in the PNW. Management of this root-tunneling pest requires a better understanding of how a Brassica cropping system and management strategies affect the maggot’s development. Growers need to take advantage of the knowledge gained from this project’s research over the past years and develop a strategic IPM tool plan that works for their personal farming system.
With increased ecological scrutiny, strict environmental regulations on chlorpyrifos use (The Clean Water Act, the Endangered Species Act, OR Senate Bill 1010, the OR Plan for Salmon and Watersheds and the Food Quality Protection Act, etc.), uncertain availability, potential pesticide resistance, and growing doubts over its efficacy, all these concerns have provided more incentive for growers to begin implementing a multi-tool approach. While historically growers have not been interested in alternatives due to low cost, the quick ‘fix,’ and the easy availability of this chemical, a combination of tools may be the only means of suppressing cabbage maggots in the Valley.
Research was conducted from January 2001 through December 2005 in the northern Willamette Valley, Oregon, where over ninety percent of Oregon’s commercial Brassica crops are grown. Our research sites consisted primarily of commercial fields of rutabaga (Brassica napus cv. Laurentian Purple Top) and turnip (Brassica campestris cv. White Globe Purple Top) within 2 km of the Willamette, Pudding, and/or Molalla rivers; however, data were also collected from rutabaga and turnip fields at Oregon State University’s Northwest Research and Extension Center (NWREC) located in Aurora, Oregon. The fields were representative of the area and varied in size from ≈1 to 4 hectares. Associated border vegetation, which may provide both food and shelter for the fly (Griffiths 1986), included trees (predominantly ash (Fraxinus), white oak (Quercus), cottonwood (Populus), maple (Acer), and Douglas fir (Pseudotsuga)), understory perennials (wild blackberry (Rubus), wild rose (Rosaceae), grasses (Graminaceae), sedges (Carex), and rushes (Juncus)), and herbaceous annuals (including wild cucumber (Echinocystis) and mustards (Brassica) and others). In addition, nurseries, hazelnut orchards, and housing developments bordered many of the fields. Soil types varied but were predominantly loams (Quatama, Newberg, Latourell) and silty loams (Willamette, Woodburn, Cloquato, and Amity). These soils are partially drained to well-drained with pH between 5.5 and 7.0.
Annual precipitation in the northern Willamette Valley is typically 110 cm with over half falling during the period December through February. Summer precipitation averages only about 8 cm. Because of light rainfall during the summer months, Brassica fields must be irrigated, mostly via overhead sprinkler irrigation. Mean daily high temperatures in the summer reach 27˚C in July, with average lows of 10˚C. In winter months the average daily maximum temperature is around 10˚C with daily lows averaging about 2ºC. The first frost is typically around 1 November. Snow and extended periods of sub-freezing temperatures are not common in the region. Four distinct seasons can be characterized by differences in precipitation, photoperiod, and temperature in the Pacific Northwest.
Weather data used in this research (air temperature and precipitation) were provided by the Pacific Northwest Cooperative Agricultural Weather Network from an agrometeorological weather station (AgriMet; #356151, latitude 45° 15 N, longitude 122° 46W, elevation 45.7 m) located at NWREC, approximately 10 km from the farthest research field. Daily minimum and maximum air temperatures recorded at 1.8 meters were used for computations in the degree-day model described below. Cumulative precipitation was collected daily for a 24 h period with a non-heated tipping bucket.
Degree-day accumulations (DD) were used as a proxy for physiological time to predict emergence and flight activity (Pruess 1983). We assumed a lower development threshold of 4.3ºC, which is generally accepted in cabbage maggot models for the northern United States (Johnsen and Gutierrez 1997, Jyoti et al. 2003), and an upper development threshold of 30º C because very few flies emerge at higher temperatures (Collier and Finch 1985). Daily DD accumulations were estimated using the single sine approximation (Baskerville and Emin 1969, Wilson and Barnett 1983). Thermal units were accumulated beginning on 1 January.
Spring Fly Emergence
Emergence cages were used to monitor spring emergence of adult flies from overwintering puparia collected the previous fall (Finch and Collier 1983). The Boll Weevil Trap (Hercon Environmental Corporation, Emigsville PA) was used as the emergence cage. The cage is a plastic cylinder, 15 cm in height and 11 cm in diameter. An inverted fine-meshed (1 mm) metal screen cone, 12 cm tall, sits on top of the cylinder with a small plastic cup fitted securely over the cone. Two emergence cages were placed in each field studied in 2001–2004; there were 3, 6, 10, and 3 fields, respectively, with each field representing a different geographic area in the production region. For each cage, ten D. radicum puparia were collected in the late fall and placed 5-6 cm below the surface of the soil with an emergence cage placed on the surface directly above the puparia. Puparia used in the emergence study were collected from a number of fall-planted Brassica fields and a wide assortment of plants within each of these fields. Cages were monitored weekly for cabbage maggot flies from 5 January through 30 June. Each week the number of flies that were recovered from the cages was recorded and cages were re-fitted with empty retaining cups.
Seasonal Flight Activit
Cabbage maggot flight activity was monitored throughout the growing season with yellow water traps (Finch 1992). Traps were fluorescent yellow plastic buckets (AmLoid Corp, standard ASTM F-963; Monterrey, Mexico), measuring 18 cm in diameter, 30 cm in depth, and a volume of 5 liters. Buckets were filled with water to within 3 cm of the rim. Two ml of 6% liquid sodium hypochlorite and a few drops of detergent were added to prevent microbial growth and reduce surface tension. Buckets were set on the soil initially and raised slightly above the plant canopy as the season progressed. Buckets were replaced with new buckets after 3 or 4 months. Fly activity was monitored in fields beginning in February and serviced weekly until November. In each field, one water trap was placed along the border of the north to northeast side of the field in the upwind direction of the prevailing wind (Finch and Skinner 1982, Banks et al.1988). Vegetation was removed from an area immediately around the trap of radius 0.5 m (Griffiths 1986). Flies were collected weekly, counted, preserved in 70% EOH, and later identified with a key (Brooks 1951). Traps were cleaned and refilled after each collection.
Plant Growth Stage
Prior to monitoring for egg incidence (oviposition) and crop damage, a plant growth stage was documented based on a 1-4 rating index of four plant growth stages (PGS). The rating was based on number of leaves, root development, and crop canopy coverage. The plant growth stages consisted of:
PGS 1: cotyledon to four developing true leaves, root diameter less than 6 mm, canopy coverage open, bare ground exposed;
PGS 2: 5-8 leaves, root diameter >6 to 19 mm, canopy coverage open, and >50% bare ground exposed;
PGS 3: 9-15 leaves, root diameter >19 to 32 mm, canopy coverage partially-closed, and < 50% bare ground exposed; and
PGS 4: 9-15 leaves, root diameter >32 mm, canopy coverage closed (typically).
The number of fields assessed yearly was: 16, 34, 20, 14, and 6, respectively. The mean number of assessments per field was seven. Mean egg incidence was computed for each plant growth stage per field.
Fields were inspected weekly for CM eggs using the egg-scrape technique (EST), similar to that described by Skinner and Finch (1986). It was modified as follows: Each field, regardless of size, was divided into six locations: four outside corners (NE, SE, NW, SW) and two central locations (midNE, midSW) (Fig. 2). Egg sampling began when plants reached the cotyledon stage. Preliminary surveys in 2000 determined that oviposition did not occur prior to cotyledon stage. To minimize edge effect, five meters of buffer rows around the perimeter of each field were excluded from sampling. At each of the six locations, plants were selected along five points of a M-shaped transect within a 15 m2 area. At each point, three neighboring plants were randomly selected, totaling 15 plants per location. A total of 90 plants per field were inspected for eggs. Around each plant, a 5 cm radius of soil was scraped away to a depth of 2 cm. The numbers of plants with eggs present were recorded. Thus, the proportion of plants with eggs present (egg incidence) could be determined. The occurrence of plants with eggs for each field was analyzed to determine for each field when egg levels significantly increased, or “spiked.” Spike dates were then plotted and analyzed to determine when increased oviposition occurred. In addition, weekly egg incidence assessments were summed to determine relationships with crop damage at harvest.
To measure crop loss from CM, a total of 180 fields were assessed for damage. Many studies have assessed crop damage in aboveground Brassicas using yield data (Bevins and Kelly 1975), numbers of tunnels (Eckenode and Chapman 1971), and rankings of damage severity (Stitt 1953). Skinner and Finch (1986) estimated CM damage by taking six 10-plant samples at random across a field of 5.0-10 hectare and evaluating the presence or absence of CM. In this study, a damage assessment was designed for the belowground Brassica crops, similar to the Skinner and Finch (1986) method, but modified as follows. Each field, regardless of size, was divided into six sections: four outside corner locations (NE, SE, NW, SW) and 2 middle locations (midNE, midSW) (Fig. 2). To minimize edge effect, five meters of buffer row were excluded from samples. Ten plants at each location were randomly selected along a zig-zag (“M”) transect of ≈15 meters into the field. The damage assessment, referred to as “M60”, was initiated at harvest. Sixty plants were removed from the field and their roots inspected for CM tunneling. The proportion of damaged roots was calculated.
The effectiveness of chlorpyrifos in reducing damage from CM was determined over a five-year period by comparing treated plants to untreated plants (no-spray) in 32 commercial growers’ rutabaga and turnip fields in the northern Valley. Each treatment consisted of three beds, four rows per bed, nine meters long, replicated two to three times. Chlorpyrifos (Lorsban 4E) was applied at a rate of 0.10 lb ai/1000 row feet, beginning with a broadcast band, not incorportated on seeded rows at planting and 3 additional foliage sprays 14 days apart. Sixty plants from each treatment were randomly selected from the center bed. Roots were examined for the presence/absence of cabbage maggot damage and the proportion of plants with damage was calculated. Pair-wise comparison t-tests (α = 0.05) were performed on treated and untreated beds in these commercial fields. The GLM procedure (ANOVA, SAS 9.1 Institute, Inc. 2003-2004) was used to test if any other factors such as crop type, year, season, and planting time affected damage levels.
Planting and Harvest Date
Each year, Brassica field plantings were selected over three distinguished seasons based on CM flight (Dreves et al. 2006): 1) spring plantings (high flight; before ≈ 900 DD; n = 61); 2) summer plantings (low flight; 900 DD to 1500 DD; n = 75); and 3) fall plantings (after 1500 DD and high flight initiated at 2100 DD; n = 47). Further, the early planted fields (n = 61) were designated as those crops planted before 95% spring CM flight (< 900 DD), (according to double gamma model from yellow water trap flight data; Dreves et al. 2006) and late-planted fields (n = 119) were those planted after 900 DD. Early harvested fields were designated as those crops harvested before the relative minimum peak of fall flight, ≈ 2600 DD and late harvest fields were designated as those crops harvested after the fall peak flight, a DD accumulation of greater than ≈ 2600 DD. The amount of time a crop remained in the field was calculated by accumulating DD from the elapsed time between planting of the crop until harvest. Damage accumulation rate, or amount of damage sustained per DD in the field, was computed by dividing the time (DD) in the field by the damage level at crop harvest.
We conducted a trial at the Montecucco Farm in Canby, Oregon, in spring 2004. The trial took place in a field planted the previous year to turnips, variety Purple Top, on August 23, 2003. The turnips were not harvested, to simulate a practice of leaving a fall crop in the ground until spring plowing. This is a common practice in the Willamette Valley during years when the market value of turnips is low or too much rain keeps a farmer from being able to work the land.
Each plot measured approx. 20 feet wide (4 beds x 5.5 ft) by 100 feet long. The following treatments were included: 1) Untreated – No action was taken. The live crop was left in the ground. Green tops were mowed off to avoid seeding on 3/12/04; 2) Rototilled – the crop was rototilled once. In this process, plants were taken completely to the ground, many roots were chopped as visually seen in the field with some roots present on the surface and others buried at a shallow depth; 3) Double-disked and deep-plowed – the crop was double-disked with two passes. A plow was then used to bury the roots to a depth of approximately eighteen inches. One pass was made (3/12) by a cultipacker (roller) to smooth and pack the topsoil to create a crust. Treatments were replicated 3 times and arranged in a randomized block design. Five emergence cages were placed randomly in each plot on March 18, 2004. Emergence cages were checked weekly for emergence, and fly counts were recorded. All flies were removed weekly from plastic dishes on top of the emergence cages.
Exclusion Fence and Row Covers
The use of Reemay, a spun polyester row-cover material, was tested as a barrier to cabbage maggot infestations in root crops. Four row cover trials were conducted in 2004 on grower’s root crop fields (turnips and daikon). Each plot consisted of four rows, 100-200 feet long and 80 feet wide. The treatments were either with or without Reemay row covers (applied at 2 weeks after planting), planted in a complete-block design with 4 replicates. At harvest, 20 roots were inspected and the number of roots with cabbage maggot damage was recorded. Means were separated by the Waller-Duncan mean separation test (SAS Institute 1999). The use of exclusion fences around Brassica fields was evaluated for efficacy in excluding cabbage flies from a turnip crop. The trial’s objective was to define an appropriate fence design for larger scale commercial use and to obtain preliminary data on the efficacy of such a design. Canadian researchers (Vernon and McGregor 1999; Vernon and Mackenzie 1998; Bomford et al. 2000) reported effectiveness of exclusion fences. The trial was not replicated. A fine nylon mesh fence (30’ x 30’) was designed by a local grower in Canby measured 135 cm high with 25-cm overhangs. We examined 60 roots inside and outside the fence, representative throughout the sampling area.
Trap crops are plants grown specifically to attract pests away from a cash crop. Trap crops can consist of a few rows adjacent to a cash crop, can be planted on all sides of the cash crop (perimeter trap cropping), or can be interspersed in a cash crop (intercropping). The preferred method depends on the crop and the mobility of the pest. Trap cropping is most effective against insects that hone in on crops unlike passively dispersed insects that go where the air currents take them, like winged aphids.
A preliminary study was conducted in the North Willamette Valley in 2005 to test the effectiveness of rutabagas as a trap crop placed on the border next to a main cash crop, turnips. An infested field of turnips (40% loss from cabbage maggots) was harvested in early June and the grower was worried about future infestations of future new plantings from migrating flies. Three rows of rutabagas were planted on 7/7/05 as a barrier trap crop to the main crop (turnips). A 3-hectare field of turnips (main crop) was planted to the east of the rutabagas on 7/21/05. Both crops were under standard management regimes. Cabbage maggot damage was evaluated in both the rutabaga trap crop and the turnip cash crop on three different dates (9/14/04, 10/6/04, and 10/17/04).
In 2004, laboratory soil bioassays of Entomopathogenic fungus treatments were applied to 2nd instar larvae and performed at economic field rates for in-furrow (3.85E+06 spores/g dry soil) and broadcast (3.85E+05 spores/g dry soil) applications with 3 isolates of Metarhizium anisopliae (F52, ATCC62176, ARSEF5520) and one isolate of Beauveria bassiana (GHA) (See journal article).
Cabbage maggots frequently require management in areas of intensive Brassica crop production, as seen in northwestern Oregon. Growers of root crops in the northern Willamette Valley are challenged to produce a crop economically, when Delia spp. are problematic through the season for rutabaga and turnip crops. This research was developed to investigate strategies for reducing CM, which most importantly included monitoring. Growers did not monitor for presence of maggot, but prophylactically treated fields, regardless of the actual level of oviposition. This research promoted monitoring in order to: 1) to assess a pest situation and determine what sort of pest activity is occurring; 2) to predict pest problems before they occur; 3) for wiser decision-making; and 4) ultimately, to reduce pesticide use. The study investigated spring emergence and seasonal flight, pest impact, relationships between flight, damage and oviposition, and timing of planting and harvesting to avoid high risk peaks of fly activity.
Below is a bulleted list of a few significant results and objective accomplishments from the research conducted in the northern Willamette Valley from year 2001 through 2005. These results contribute greatly to reducing chlorpyrifos use in Brassica crop production. Our intentions were to promote practical, economic and achievable solutions to increase the probability of adoption and success. The results of our investigation, (as described below) have been disseminated through various means such as newsletters, flyers, one-on-one grower discussions, workshops, and professional meetings (See Publications and Outreach). We published 2 refereed journal articles (Appendix: Journal of Invertebrate Pathology and Environmental Entomology) and three more are being reviewed for publication. Two extension bulletins should be completed by the end of the year describing life biology, monitoring, and management.
The following is the beginning of a list of recommendations to growers to help reduce levels of cabbage maggots in rutabaga and turnip root crops:
Develop a planting and harvesting schedule for anticipated field plantings. Evade planting during peak egg-laying periods in the spring (before 900 DD). Acknowledge that a field is at risk if left in the ground over fall flight (>2100 DD). Rotate new plantings away from overwintering (last fall’s plantings) and highly infested seasonal maggot sources. Cabbage root flies are noted to be weak fliers, so crop rotation can be a highly effective strategy against this pest. The newly planted field must be situated at a sufficient distance (ca. 1000 meters) from a maggot source to discourage relocation of CM.
Lorsban has its drawbacks including limited effectiveness and uncertainty about human health and environmental effects. An adult-egg monitoring-based program should be implemented to determine actual need of control. Use of water traps to detect the end of spring flight to time first planting is worthwhile. Set up yellow water traps on border of newly planted fields (corners of prevailing windward wind). Document weekly trap catches and pay attention to low and high patterns of fly catch. Water traps are not foolproof. If >100 flies are caught in traps over the duration a field is in the ground (7 weeks), there is potential for greater damage (> 20%).
Predict emergence and flight by using the Oregon degree-day model and record daily degree-days. Monitor weekly yellow water traps to document the actual arrival of flies by recording number of flies in traps.
Monitor weekly for egg levels to verify oviposition in field. Begin sampling at approx. 3 weeks after planting (>5 leaf stage; >6 mm root size) to detect increases in oviposition, which is essential for timing treatments and effectively targeting eggs at the base of plants. If greater than 10% of plants are assessed with eggs in a field, consider treatment. This research showed that less than half the sum of percent egg incidence (no. of plants with eggs) assessed weekly actually acquired damage.
Rutabaga crops incurred more damage than turnips in this study. Consider planting 2 – 3 rows of rutabagas on border of fields to attract flies away from the main crop, but remember to destroy those rows before that next generation of flies reproduces. However, damage leveled off in the field the longer the rutabaga crop was in the ground, perhaps due to the roots’ ability to heal.
Assess fields periodically for damage levels using the binomial procedure (60 roots) to confirm the level of damage relative to oviposition in order to meet market demands.
Consider destroying a highly damaged root crop (> 40%) early to avoid fly movement into nearby fields.
Harvest roots in a timely fashion to avoid risk of future damage.
Delay seeding until after the first spring generation flies have passed (>900 DD- See degree-day model below) and harvest before fall generation flies appear in late August.
Time treatments at high pest risk to crop which is typically the later stages of plant growth.
Monitor for eggs to verify actual egg incidence.
Destroy wild cruciferous hosts (wild mustard, black mustard, yellow rocket, wild radish) by removing from field.
An insecticide may be applied as an in-furrow or incorporated application at planting to control first-generation larvae. Focus on spring generation control to reduce future maggot activity.
Insecticides have limited effectiveness against adults, due to the behavioral patterns of the pest. The fly spends most of its time at the periphery of the fields, flying into the field to lay eggs at the base of the Brassicas, and then leaving the field. After eggs hatch, the larva feed on the root and eventually pupates in the soil. When the adult emerges from the pupal case, it flies to the periphery of the field. This behavioral pattern leaves only limited opportunities for control of adults with insecticides.
Brassica plants produce isothiocyanates and other glucosinolate compounds when growing or when stressed by environmental conditions, such as low temperatures or by insect damage, which helps explain why fields with damage become very attractive to egg-laying adults. This information is important when developing a monitoring program and knowing when the best time to begin monitoring.
Row covers can protect newly seeded beds if secured properly, however it can be labor intensive and costly. A breathable, low heat absorbent row cover material (shade clothe or light-weight Reemay) applied in the spring. Summer row covers may not work in Oregon due to overheating and plant’s desire for cool conditions. The material should be lightweight, allowing light, air, and water to pass in. The row cover must be securely anchored into the soil around a newly seeded field and undamaged to be effective in excluding egg-laying flies from the plants. Enough slack left to allow for the plants’ growth. However the covers can interfere significantly with crop maintenance so may have to be removed once for cultivation (weed) purposes at early stages of plant growth.
Cull piles are breeding grounds for the top layer of roots piled in a field. Either bury culls or chop them up to avoid cabbage maggot population build-up.
Spring emergence of CM flies in field emergence cages indicated a bimodal spring emergence pattern. Approximately 70% of the overwintering population emerges and displays an early peak in late March, while the remainder of flies emerge later in the spring, displaying a smaller peak in late May. The mean degree-day (DD) accumulations at 10, 50, and 95% of spring emergence using a lower and upper developmental threshold of 4.3°C and 30°C beginning 1 January had corresponding DD values of 200 ± 50.2 (8 March), 330 ± 22.2 (4 April) and 762 ± 60.1 (28 May), respectively.
Flies caught in yellow water traps mirrored the bimodal emergence pattern, but with a delay of 3 days to 5 weeks. The mean DD accumulations recorded from the beginning to the end of spring flight had corresponding DD values of 303 ± 61.5 (31 March) to 839 ± 51.9 (4 June). Fly activity was lower over the summer from the beginning of June until the end of August (2138 ± 82.3 DD). A fall emergence of flies was observed each year beginning in late August to early September and extending through October (2860 ± 170.6 DD).
Overall, crop damage from CM was assessed using a binomial sampling procedure of 60 roots per field. During the course of the study, harvest damage increased from a mean damage of 11.9% (± 2.5) in 2001 to 41.4% (± 5.5) in 2005. Rutabaga crops sustained greater percent root damage (37.9 ± 3.4) than did turnip crops (22.9 ± 1.8). Crop damage was significantly greater (37-52%) in crops planted during the spring before an accumulated 900 degree-days, when compared to crops planted in the summer (>900 DD) or fall (>1500 DD). When planting occurs after 900 DD, and the crop is harvested prior to the peak of fall flight (< 2600 degree-days), damage from maggots is reduced substantially. A significant relationship was seen between fly catch and crop damage observed at harvest (r2 = 0.64; P < 0.0001). Fields with seasonal counts of fewer than 100 flies per trap over a crop’s duration in the field had a lower sum of weekly assessments (avg. 6) of plants with one or more eggs, averaging 38.6 ± 6.1, and had less than 20% crop damage. Fields with seasonal counts greater than 100 flies per trap had a higher sum of weekly assessments of plants with eggs, averaging 95.6 ± 6.7 and greater than 20% damage at harvest. Data showed that if greater than 10% egg incidence is reported at any given evaluation, control should be considered. It is felt that fly counts in water traps are not reliable indicators of a potential problem, and egg monitoring is essential to verify arrival of ovipositing females in a field. Interestingly in this study, the sum of weekly egg incidence assessments per field resulted in half the amount of actual damage recorded at harvest. Planting date predicted occurrence of oviposition better than did flight events. Oviposition significantly increased in fields at 30.9 (± 1.1) days after planting. However, some summer-planted fields were without a significant number of plants with eggs until the later flight of the fall generation. Precipitation did not appear to be a significant factor affecting the oviposition timing in these eight fields. Water trap catch was unreliable as a predictor of actual timing of oviposition in the Brassica field but can alert growers of potential damage and oviposition levels. Increased egg incidence was recorded on older plants with > 5 leaves, root diameters of > 6 mm, and an increased crop canopy. There was a significant correlation between egg incidence and damage at harvest; in particular the sum of weekly egg incidence assessments from later plant growth stages showed the strongest relationship with crop damage (r2 = .84). Egg incidence was significantly higher (46%) on plants located on the outside periphery of fields than centrally located plants.
Additional results and accomplishments are
Monitoring (Pest Scouting)
Monitoring of cabbage maggot population is the most important component in the success of using reduced-risk strategies. Without a monitoring plan, implementation of a chemical control or other practice can be poorly timed and subsequent controls are inadequate for the method to be acceptable. This research study addressed monitoring techniques.
A. Spring emergence and seasonal flight activity: Spring emergence and seasonal flight activity of the cabbage maggot, Delia radicum (L.) (Diptera: Anthomyiidae), were monitored in the northern Willamette Valley in western Oregon from 2001 through 2005. Spring emergence from overwintering puparia was monitored using emergence cages. A bimodal spring emergence pattern was observed, with approximately 71% of the spring population emerging in an early peak in late March, two months before a later peak near the first of June. The mean DD accumulations at 10, 50, and 95% of spring emergence using a lower and upper developmental threshold of 4.3°C and 30°C beginning January 1 and the single sine approximation method, had corresponding DD values of 200 ± 50.2 (Mar 8), 330 ± 22.2 (Apr 4) and 762 ± 60.1 (May 28), respectively (Table 1). Seasonal flight activity was monitored using yellow water traps. More flies were caught in prevailing wind directions than otherwise (Fig. 3). The yellow water trap proved to be an effective trap for measuring flight trends. Spring flight patterns mirrored the bimodal emergence patterns but with a delay of 5 days to three weeks between emergence and detection of flies in the water traps (Fig. 4 and 5). The mean DD accumulations recorded from the beginning to the end of spring flight had corresponding DD values of 303 ± 61.5 (Mar 31) to 839 ± 51.9 (June 4) (Table 2). Fly activity was lower over the summer from the beginning of June until the end of August (2138 ± 82.3DD) (Fig. 6). A fall flush of activity was observed each year beginning in late August to early September and extending through October (2860 ± 170.6 DD) (Table 3).
The four seasons in the northern Willamette Valley of western Oregon are characterized by differences in precipitation, photoperiod, and temperatures. The seasons coincide closely with distinct phases in the cabbage maggot life cycle as seen in this project study:
Spring: emergence of overwintering puparia,
Summer: reduced flight activity,
Fall: flush of flight activity,
Winter: puparia undergo diapause.
Broad seasonal patterns of adult D. radicum activity were similar from year to year: a bimodal emergence pattern in the spring with approximately 45% of total annual of flight activity, lower levels of activity in the summer with approximately 17% of total annual of flight activity, and increased activity again in the fall, with 38% of total annual flight activity. However, the timing of spring emergence and fall flight as a function of DD accumulations can vary widely, even within a relatively small region like the northern Willamette Valley. In our 4-yr study of D. radicum populations in the Willamette Valley, timing of spring emergence and initiation of fall flight of D. radicum adults could be predicted with a simple DD model only to within about 10 days; however, the DD-based predictions were substantially more precise than those based on calendar date alone. A simple DD model omits important primary variables such as moisture, photoperiod, and average daily maximum temperatures, and these omissions contribute to the degree of uncertainty in predicting the timing of adult activity. Some variables with indirect effects on D. radicum phenology are also likely to contribute to the variability. For example, heavier soils tend to warm up more slowly than lighter textured soils, so flies emerge earlier in sandy loam soils than clay loam soils (Read 1958). It is possible that variation could be reduced somewhat by basing DD models on soil temperatures at individual sites rather than air temperatures at a central regional location (Collier and Finch 1985); however, because of the many sources of variation, it is questionable how valuable more accurate measures of temperature would be in terms of predicting adult activity.
In addition, the difficulty of obtaining such data would preclude the development of practical, region-wide alert systems for fly emergence based on soil temperatures.
Despite the imprecision of DD accumulation as an exact predictor of the timing of activity peaks, DD accumulations provide valuable information that complement flight activity collected from yellow water traps. For example, after water trap counts indicate the beginning of the spring emergence period, the flight activity levels may drop rapidly. However, the DD model predicts a late peak in activity at around 750–800 DD and therefore a continuing threat of high fly activity until DD accumulation of around 900. In addition, the precise timing of the peak and end of the flight can only be confirmed by the water trap data. When the spring flight slows down at approximately mid June, low adult activity levels can be expected until the onset of the fall flight near the end of August.
Understanding flight behavior of D. radicum adults is a potentially valuable first step toward managing CM populations in Brassica crops. However, the relationships between adult flight activity, oviposition, crop damage, and environmental conditions must be understood before specific management recommendations can be made. Some possible management strategies would be to use monitoring and modeling to optimize the timing of: (i) planting and harvesting to avoid high adult activity peaks and oviposition, (ii) insecticide treatments, to coincide with high adult flight and subsequent oviposition activity, or (iii) the application of physical barriers such as row covers or exclusion fences just prior to flight activity peaks.
Egg inspections should occur weekly starting after the plant development of 5 leaf stage when egg levels begin. Higher egg counts were seen 30 days after planting (Fig. 7) on older plants (>1/4 inch root, 5-9 leaf stage, increased canopy) than younger plants (cotyledons, <5 leaf) (Fig. 8). However if maggot pressure is high and the preferred stage is not available, then flies will lay eggs on other plant stages. There was approx. two-three times more egg incidence observed than the amount of damage assessed at harvest. Desiccation, natural mortality, chemical control, and biological control were some of the factors contributing to egg mortality. Supporting data also revealed that eggs laid by females during early plant growth stages are better controlled by treatments than if laid later after the plant canopy closes. Cabbage maggot damage was not seen on the roots when eggs were laid on plants within 10 days of harvest. Crop Damage Root damage caused by cabbage maggots can be easily quantified by a visual inspection of roots representative in the field. Once the roots start developing (1/4 inch), a field can be inspected for damage. A field is divided into 6 areas, which includes the 4 corners and 2 middle sections. Ten roots are examined for CM damage. The proportion of damaged roots is calculated. A sequential sampling plan (speed-scouting) is being reviewed to provide a quicker assessment to determine low and critical high damage levels for growers needs. Crops planted early in the spring (before 95% spring flight; < 900 DD) had significantly more damage than did late-planted crops (after 95% spring flight; ≥ 900 DD) (F = 19.62; df = 2, 178; P < 0.0001) (Fig. 9). Fly catch (based on a total of 7 assessments was moderately correlated with damage at harvest (r = 0.64; P = 0.0001; r2 = 0.41) (Fig. 10). Total fly catch in fields with less than 20% damage, averaged 70.8 ± 7.1 (n = 36), while fields with greater than 20% damage, averaged a fly catch of 248.6 ± 30.3 (n =35) (Fig.11). B. Spatial management – Mapping fields with flight, oviposition, and seasonal The GIS-IPM mapping tool can be effective for identifying low- and high-risk maggot areas in a region and provides a useful presentation as to what is happening in the region. Certain conditions favor cabbage maggot infestations as seen visually on a map prepared by Excel-based GIS system. In commercial plantings many of these conditions can be avoided. Such conditions that proved to be statistically significant from this spatial research include: Planting neighboring fields in succession seems to increase risk in later plantings as flies move from harvested fields to neighboring fields. Consecutive annual plantings of Brassicas could prove damaging especially if a field is planted adjacent to field with existing high damage. Plantings near overwintering sources raise the risk of damage in the spring. Fields planted near abundant wild Brassica weed hosts (wild radish, black radish, yellow skyrocket, wild mustard) and cull piles had higher damage rates. Sanitation is an important practice. Fields surrounded by brush barriers and woods, a place of rest and feeding were notably higher. Fields planted adjacent to houses, nurseries, and other buildings may need special attention to monitoring as they proved to have higher damage. Fields that are separated in time (>550DD) and space (>225 m = .14 mile) from infested fields had less damage.
Avoid planting in spring when fly densities in water traps are high. Plantings in the spring had higher levels of damage, so early plantings should be avoided.
Presently, many of the cooperating growers are not computer savvy so access to available and updated degree-day values, flight, eggs, and damage levels are more difficult. In the meantime, the GIS-Mapping computer program will need further refining to develop a useable product. Documenting field information and mapping seasonal CM levels (such as flight, egg incidence, and seasonal and harvest damages) may be more useful to a grower.
C. Cultivation. Spring and fall tillage (disking or plowing) can reduce CM spring emergence. The fall and spring cultivation trials supported this hypothesis. There were significant differences in numbers of emerged flies between treatments. The untreated plot had significantly more flies than both cultivation treatments (Fig. 12). There was double the number of flies recorded in cages in the untreated plots than in the cultivated plots. No significant differences in numbers of flies were observed between the rototilling and double-disking/deep plowing treatments. Cultivation may be a good tool to help reduce the load of emerging populations.
D. Biologicial Control. All isolates tested in the laboratory study killed D. radicum 2nd instar larvae (Fig. 13). The conditionally registered (with the US Environmental Protection Agency) M. anisopliae isolate (F52) performed best, killing an average of 85 and 72% of D. radicum larvae at the high and low concentration, respectively. The mean concentration of F52 spores required to kill 50 and 95% of 2nd instar D. radicum was 2.7E+06 and 1.8E+08 spores /g dry soil, effectively, requiring approximately 20% of the recommended rate (i.e. the middle of the field remaining untreated).
E. Planting and Harvesting Schedules. The effects of manipulating sowing and harvest dates on the degree of cabbage maggot damage on turnips and rutabagas were investigated on fresh market farms in the northern Valley. The proportion of damaged turnips and rutabagas resulting from late plantings (after the first week in June) and harvested before the fall generations was lower than those sown earlier (spring season; ~900DD). There were low numbers of flies caught from mid June to late August, and very high numbers of first-generation flies caught from early March to early June. A fall sowings (August 1), in combination with a harvest before the last peak of the fall generation flight activity, resulted in a higher proportion of marketable roots.
Planting and harvest schedules could be adjusted to avoid crop exposure to periods of high-risk fly activity, and pest management practices (e.g., chemicals, row covers, exclusion fences) could be timed to be most effective. For example, when fields were planted after spring flight (>900 DD) and harvested before fall flight (<2138 DD), lower damage was recorded.
F. Trap Cropping.
Significantly more damage was found in the 3 rows of rutababas compared to the main crop (turnips). However the trap crop was not destroyed before the next generation emerged, so the main crop was re-infested as detected at the Oct. 17 evaluation (Fig. 14).
Review of Accomplishments for Objective 1.
Harvest damage was assessed in the northern Valley region in 2001 through 2005 with the use of a technique termed “M60” as described below.
Ten un-replicated no-spray field plots were installed in grower fields in 2003. Four replicated no-spray plots were installed in grower fields in 2004. Treated plots were sprayed at 14-day intervals with Lorsban 4E.
Preliminary analyses indicate that there is a relationship between crop planting date and damage levels. However, there are many factors other than CM phenology that impact damage, including management practices, landscape factors, a field’s proximity to other infested fields, and crop developmental stage.
Growing of long-season root crops can be attacked by 2 generations of flies, but damage was most severe during the spring (mid March and early May) and fall (early Sept to mid October). Aboveground crops including broccoli and cauliflower were most vulnerable during the first 5-6 weeks after transplanting, but little to no yield loss was shown. It is best to protect plants in the first 4 weeks of transplanting.
Data analyses indicate that damage levels were lower in fields planted in the summer and fall (August) at > 900 DD.
Planting later in the season (> 900 DD; ~after June 1st) and harvesting before fall flight (< 2600 DD; Sept 1st) to avoid high-risk attack from cabbage maggots may be an effective strategy. In general, damage levels were not significantly different in no-spray plots when compared to the conventionally managed chemically treated plots in rutabaga and turnip fields. Accomplishments for Objective 2. 2a. Develop a regional degree-day model. Predicting adult flight through the use of a degree-day (DD) model could help growers to both eliminate sprays and improve the timing of sprays. Our DD model was based on models from other parts of the U.S. and beyond (e.g. New York, North Carolina, SW Ontario, Wellesbourne, England). The daily average DD were accumulated using a single sine approximation method and a low and high developmental threshold of 4.3 °C and 30 °C, respectively, beginning January 1. To develop and validate the DD model, adult flight was monitored through the use of emergent cages and yellow water traps over a 4-year period (2001 through 2004). A trap placement study was also initiated to evaluate the optimal placement of water traps for quantifying adult flight. Spring emergence: a) Overwintering pupae were collected from infested fields located at the NWREC station each fall. Twenty pupae were buried under each emergent cage in commercial fields in the northern Valley. Cages were monitored weekly for adult captures from January 5 through July 1, after last emergence of adults. b) Temperature data were collected from Aurora Agrimet Weather Station and degree days were computed. Spring emergence was related to cumulative degree-days. Seasonal adult flight: a) Individual yellow water traps were placed each year in Brassica fields to follow patterns and trends in flight around the northern production region throughout the year. b) An OSU Extension regional pest monitoring program, VegNet, adopted the CM monitoring program and monitored adult flight at 8 additional locations throughout the Willamette Valley in 2002-03. Placement of Water Traps: a) To better understand fly movement in the field and optimize the location of traps within a field, a trap placement study was conducted at 5 commercial turnip fields in the northern Willamette Valley. Results of Obj 2a:
Water trap data indicate that there are 3-5 CM flights each year in the northern Willamette Valley of western Oregon.
The DD model may be a viable strategy for predicting spring emergence and the beginning of fall flight. The degree-day accumulation also provides valuable context for interpretation of adult fly population data from yellow water traps. A bimodal spring emergence pattern was observed as noted by other researchers. Early-emerging flies, constituted approximately 70% of the spring population, while only about 30% were late-emerging flies. The strategy of trying to plant crops between the early and late spring peak is not likely to be effective as it would be hard to predict and fly pressure is more or less constant throughout the spring season. By the end of spring emergence (approx. June 1s approximately 850 DD), CM flight activity decreased markedly over the summer months. A notable increase in fly activity increased again with DD accumulation of 2138, approximately Sept 1. (Appendix-Table 1 & 2, Fig. 3).
The yellow water traps were adequate for monitoring seasonal trends in CM adult activity (Appendix- Fig. 6). Abundant rainfall following the onset of emergence may contribute to increased emergence and flight activity. We observed delays of 5 days to 3 weeks between fly emergence (measured by emergence traps) and flight activity (detected by water trap catches) (Appendix- Fig.4 ).
More flies were captured in water traps at the northeast and eastern borders of fields than the southwest field borders. Data indicate that flies migrate upwind to the traps as prevailing winds have been recorded from the southwest. This information will be used to improve the efficacy of adult flight monitoring through the use of water traps (Appendix- Fig. 3).
Water traps can not be used as predictors of damage levels but can alert a grower of when flies may be entering a field and warn them of potential egg-laying events.
Preliminary analyses indicate that there is a linear relationship between crop planting date and damage levels. However, many factors other than CM phenology impact damage, including management practices, landscape factors, a field’s proximity to other infested fields, and crop developmental stage.
Can we predict the potential risk of a particulate field? Yes, it may be possible through a combination of applying a degree-day model, improved monitoring of adult flies, understanding the relative attractiveness of crop developmental stages, and determining how far the field is from an infested field.
2b. Implement a viable monitoring system (eggs, plant damage)
For sampling methods to be considered viable by growers, they must be practical, reliable and cost effective.
Results of Obj 2b:
The “M60” is a conservative and reliable method for assessing crop damage.
The “ES90” is a tedious, strenuous but accurate technique for measuring egg levels in a field.
There is a positive relationship between cumulative assessments (6 weekly assessments) of percent plants with eggs (egg incidence) and crop damage. When weekly assessments are less than 10% plants with eggs, damage at harvest proved to be less than 20%.
Fly attractiveness for egg-laying is impacted by crop development stage. Flies preferentially lay eggs at the base of root crop plants with 5-9 developing leaves (3-4 weeks after planting). However, flies will lay eggs on older plants, if the preferred stage is not available.
2c. Identify alternate chemistries and pesticide application techniques
Laboratory soil bioassays were performed at economic field rates for in-furrow (3.85 x 106 spores/g dry soil) and broadcast (3.85 x 105 spores/g dry soil) applications with 3 entomopathogenic fungal isolates of Metarhizium anisopliae (F52, ATCC62176, and ARSEF5520) and one isolate of Beauveria bassiana (GHA).
The efficacy of Lorsban, Fipronil, and Spinosad as seed treatments and applied using in-furrow and over-the-row application techniques was performed. Three on-farm trials with growers’ assistance were conducted in 2003 and two were conducted in 2004.
Examination of adult foliar treatments were conducted in 2003 and 2004 at the NWREC Station (Aurora, OR) in collaboration with Bob McReynolds, Vegetable Extension.
Results of Obj 2c:
Laboratory bioassays indicate that some strains of fungal biocontrol agents have efficacy. Teanure (F52), a Metarhizium strain, performed best killing an average of 85 and 72% of D. radicum larvae at the high and low concentration, respectively. (Appendix- Fig. 13). (Bruck, Snelling, Dreves, and Jaronski 2004, in review).
There may be CM resistance to Lorsban as has been shown previously by Canadian researchers (Zimmerman, Ministry of Agriculture 2004). In 2004, five root crop fields resulted in >80% damage even though 4 applications of Lorsban 4E was applied during the season (Appendix – Table 5). Root damage from CM has only increased each year from 2001 to 2005 (Appendix-Table 4).
Fipronil (Regent) (applied in-furrow) and Fipronil seed treatments revealed efficacious results as an alternative chemistry (Appendix-Table 6). Chlorpyrifos- (Lorsban 4E), Spinosad- (Entrust), and Fipronil-treated seeds showed promising results for control of CM, but these treatments lost their protection at 4-5 weeks after planting (Appendix – Table 7). Seed treatments use 88% less insecticide than broadcast applications. In-furrow applications were significantly more effective compared to over-the-row applications. Mustang, Calypso, Neemix, Cruiser, Gaucho, and Poncho 600 treatments showed little to no efficacy for CM larvae control.
Maggot pressure is not as evident on short-term (23-30 days) radish production because the insecticide at planting appears to provide adequate protection, if you miss the high-risk egg-laying window.
A Section 18 for fipronil application was granted to our Oregon growers in 2006, based on our efficacy data. We are also requesting from IR-4 the use of Spinosad and Warrior, an adult foliar, in turnips, radish, and rutabagas.
2d. Evaluate cultivation strategies to reduce overwintering CM populations
We evaluated both fall and spring tillage practices to reduce overwintering puparia load and thereby spring emergence. The fall cultivation trial was conducted in 2002-03 located at the NWREC station in Canby, OR. A second trial was carried out in the spring of 2004 on a grower’s field also located in Canby, OR. Emergence cages were used to trap adult flies as they emerged from the soil in the spring. The trial consisted of a randomized block design, replicated 3x with 3 treatments including: 1) untreated (no action was taken; live mature crop was left in the ground over the winter months; 2) double-disked, and 3) double-disked and deep plowed (18”).
Results of Obj 2d:
Research conducted in the fall of 2002 suggested the double-disking and deep plowing reduced spring emergence of CM in 2003. However, numbers of flies captured under each cage was variable within treatments. Increased numbers of sample cages are necessary to reduce variability.
A second cultivation trial was conducted during the spring of 2004 and preliminary analysis suggested that field cultivation in the spring reduces CM emergence. There were significant differences in numbers of emerged flies between treatments. The uncultivated treatment had significantly more flies emerge than both cultivation treatments. There was double the number of flies in cages recorded in the untreated plots than in the cultivation cage plots. There were no significant differences in numbers of flies observed between the rototilling and double-disking/deep plowing treatments. More research and replicated trials are needed to further test efficacy of cultivation practice as a reliable management strategy.
2e. Evaluate row cover and exclusion fence usage for managing CM.
Results of Obj 2e:
The row cover dramatically reduced populations of cabbage maggots, but aphid populations and bacterial soft rot (due to excessive humidity) were increased in some plots. Marketable yields were substantially higher under the row covers quantified in Trial 1. (Appendix- Table 8). Although row covers are quite expensive, our data suggest that row covers provided economic returns primarily because of an increase in early harvest when the market prices are high, an increase in crop yield, and because row covers can be used several years in a row if care is taken. It is anticipated that fewer sprays would be required using this strategy.
Based on current results from an unreplicated study, reduced numbers of damaged roots were reported in the enclosed turnip plot than the plot in an open area without a fence. Twenty percent of roots were damaged from cabbage maggots outside of the fence and only 1.3% root damage inside of fence. The fence excluded 93% of cabbage flies from entering the host crop. The results were promising and the grower has indicated that he would like to replicate the study in 2005 and is willing to take on the expense.
2f. Develop a GIS tool to assist growers in spatial CM management
There are many commercially available GIS software packages, but most of these are expensive, difficult to use, and require a significant time commitment to master. Our approach has been to add GIS capabilities to software programs that growers are already familiar with. A model CM GIS-IPM tool has been developed and is being refined to: 1) serve as a research tool to develop risk assessment criteria and evaluate CM dynamics in time and space, and 2) assist growers in regional spatial CM management. This GIS provides risk analysis, mapping and visualization tools within Microsoft Excel that supplement standard data entry and spreadsheet analyses. Data can also be exported or imported in formats that are compatible with most GIS packages.
Results of Obj 2f:
The application of the GIS-IPM tool is under development. The GIS-IPM tool will locate and map CM incidence across the region in time and space and relate damage levels to distance from previously infested fields. Fields at risk and the severity of this risk can be identified using many different user defined risk assignment criteria. Ultimately, a regional community of growers could use this tool to better manage plantings in space and time and thereby minimize pest infestations.
The program is multifunctional. It has the ability to conduct complex queries that allow researchers to analyze risk factors in detail. At the same time, it acts as a user-friendly program that allows growers to access numerous maps by simply pointing and clicking a mouse.
The CM is an ideal model for our GIS-IPM tool, as it is mobile (flight distances up to 1 mile). Due to CM’s high mobility, infested farms put their neighbors at risk. We hypothesize that growers can decrease CM infestation levels by coordinating crop rotations with neighboring growers.
The shape file-GIS interface also can benefit growers by displaying current monitoring data. Cabbage maggot eggs can hatch in as few as three days, and larval penetration of the root occurs soon thereafter. Therefore, timing of insecticide application is critical. The ability to view current, near real-time monitoring data will assist growers in making treatment decisions. This could also reduce pesticide use, as chemical applications could be made on an as-need basis.
The software is a research tool that can be used by scientists to create an extension tool. It allows researchers to test for the utility of different methods of calculating a field’s potential risk. Scientists can test their proposed rotation management systems using past data. Once an accurate model has been developed, growers can use the program to monitor insect levels in their fields, calculate potential risk levels, and rotate plantings.
Accomplishments for Objectives 3 and 4:
Held 3 grower workshops in 2004 and 3 in 2005.
Presented MagNet research at the annual 2004 Entomological Society of America meetings and co-moderated a Maggot Symposium. Title of talk was: Know thy enemy: strategies for the managing the cabbage maggot, Delia radicum L.
Developed, distributed, and trained grower’s staff to use grower-friendly CM monitoring techniques.
Created informational laminated cards on monitoring and management.
Produced five newsletters (See Appendix).
Developed a MagNet website (http://oregonstate.edu/magnet/).
Developing a grower practice survey, called the” PEST Plan.” This tool can be used by growers and program staff to evaluate grower practices and IPM adoption over time.
An OSU Extension regional pest monitoring program adopted our CM monitoring program and monitored adult flight at 8 additional locations throughout the Willamette Valley.
Results of Objectives 3 and 4:
Growers called us regularly inquiring about egg levels, damage, and flight levels. They have taken an active interest in obtaining information about CM (Appendix- pictures).
One grower hired an employee in November 2004 for 18 months who helped in technical transfer of monitoring techniques and record keeping, evaluated speed scouting, tested new chemicals and application equipment, and experimented with trap cropping and cultivation techniques.
We documented 8 cases in which cooperating pilot growers have not sprayed a field because we reported low egg numbers in that field. Also, 4 fields were harvested early based on a high damage assessment. Four fields were removed in a timely fashion based on a damage assessment to avoid further movement of CM.
One of our cooperating growers designed an exclusion fence, reported in our summer newsletter, which provided a barrier around a field; which has been reported to reduce the number of flies entering a field, thus less damage.
The primary objectives of the MagNet project are to reduce broad-spectrum pesticide use and expand grower interest in and adoption of IPM tools for and the western United States. In addition, much of the information and tools developed by the project can be utilized in other regions affected by CM. “The PEST Plan” will be a great prototype for measuring impact of IPM programs in other crops with pest problems.
Development of a degree-day model. The degree-day model developed for CM in Oregon will be posted on the IPPC On-line phenology website (http://ippc2.orst.edu/cgi-bin/ddmodel.pl?) in hopes of reducing pesticide use by better timing pesticide applications to pest incidence and identifying periods that are of low risk.
Use of monitoring tools. Commercially viable monitoring techniques will permit growers to quantify infestation levels, evaluate treatment options, and determine risk levels in individual Brassica fields.
Creation of GIS-IPM mapping tool. The development of the GIS-IPM tool for analyzing field pest risk will locate and map CM incidence across the region in time and space and relate damage levels to distance from previously infested fields. Ultimately, this tool could be used by a regional community of growers to better manage plantings in space and time and thereby minimize pest infestations. This tool is being developed with the intention of implementing a regionwide detection and warning system for cabbage maggot presence in the northern Willamette Valley.
Measuring IPM Impact. The “PEST Plan,” a grower IPM practices rating system, will measure a grower’s advancement towards ecologically based management rather than chemically intensive pest management.
Identifying alternative chemistries and improved application product uses. After 4 years of trials researching alternative chemistries, 1 product was accepted for a Emergence Section 18 in 2006 to provide growers with chemical choices to help reduce resistance possibilities.
Education and Training. The following products have been produced by the MagNet team and distributed to the pilot growers and workshop attendees: Maggot Mania newsletters, a MagNet website, a monitoring kit (water trap and recording card, hand lens, viewing jar, miniature emergent cage), and 3×4-inch laminated educational training cards that fit on a key ring. These cards have also been distributed in SW Canada in spring 2004. Growers and agricultural professionals in other CM-affected regions could benefit from these educational cards as a reference tool and reminder of tool choices.
Professional Meetings. MagNet staff have presented program results at many grower and scientific meetings and have exchanged IPM ideas with other worldwide researchers.
Production of articles, newletters, etc. The degree-day model and results on the use of a fungal agent as control for CM have been published in the Journal of Economic Entomology and Journal of Invertebrate Pathology, respectively. We intend to submit three other articles in peer-reviewed journals including regionwide monitoring strategies, the GIS-IPM tool, spatial-temporal management of CM, and the PEST Plan
Educational & Outreach Activities
Produced 5 newsletters called “Maggot Mania News” for growers highlighting pesticide resistance, degree-day modeling, spatial rotation and mapping, sampling techniques, and other alternative management methods. 2003-2005.
Bruck, D.J., Snelling, J., Dreves A. J. , Jaronski, S. 2005. Laboratory bioassays of entomopathogenic fungi for control of Delia radicum (l.) larvae. Journal of Invertebrate Pathology. 89:179-183.
Dreves, A. J., D. Dalthorp, A. G. Stone, and G. Fisher. Spring emergence and seasonal flight activity of adult cabbage maggots, Delia radicum (L.) (Diptera: Anthomyiidae) in western Oregon. Environmental Entomology. 35 (2) 465-475.
Dreves, A. J.D. Dalthorp, D. Bruck. Monitoring crop loss by cabbage maggot, Delia radicum L. (Diptera: Anthomyiidae), in Oregon Brassica root crops. (in review).
Dreves, A.J., D. Dalthorp. Seasonal oviposition by Delia radicum L. in rutabaga and turnip crops in Oregon. Environ. Entomol. In review.
Herring, P. 2005. Urban Farmer. Oregon’s Agricultural Progress. Summer 2005.
Dalthorp, D, and A. J. Dreves. Temporal and spatial management of cabbage maggots, Delia radicum (L.) (Diptera: Anthomyiidae). (in progress).
Oregon State University Extension Bulletins titled, “Take a Closer Look: life cycle and biology of the cabbage maggot in Oregon”. (In progress)
Oregon State University Extension bulletin titled, Take a Closer Look: Monitoring and Management of cabbage maggots. (In progress).
Created laminated educational 3” x 4” cards contained on a ring outlining monitoring and IPM practices in bulleted format for easy grower use.
Outreach: symposia, invited presentations, workshops, etc
Nov 20, 02 Fort Lauderdale FL Annual Entomological Society of America Meeting Presentation & titled: MagNet: Insights into the Management of Root Maggots (Delia radicum) in Brassicaceae Crops
Dec 13, 02 OSU Corvallis OR OSU-IPPC Round Table Discussion on IPM in Oregon: 15 minute talk on Cabbage Root Fly (Delia radicum) Management on a Regional Scale. Included Approaches, Limitations, Outcomes
Mar 1, 03 OSU; Hort Maggot Mania Newsletter #1 released to growers-Spring Issue 03 (introduce project and objectives)
Mar 1, 03 NWREC Station-Aurora OR “GIS Regional Mapping Computer Demonstration- Why and Why not?”Hands-on Workshop: Grower Input, Computer Use for mapping
Apr 8, 03 Indianapolis IN Fourth National Integrated Pest Management Symposium-Poster MagNet: Maggot Management- IPM and GIS mapping
June 15, 03 Wash DC Invited Organic Transitions Grant Review Panel Member
June 23, 03 VancouverWA EPA work planning meeting: Special Guest Talk–“Building an IPM Program and Ways to Measure Success”
June 26, 03 Aurora OR “MagNet”: IPM strategies including Monitoring, Mapping and Treatment. 3 Hour Hands-on Field Day, which included: Monitoring adult flight with yellow water traps; Assessing egg levels in a field to target high infestation levels; Understanding life cycle & identification of fly; Mapping damage using GIS techniques to more effectively time plantings; Application techniques to increase effectiveness & timing of treatments
July 1, 03 Corvallis OR 6 additional Laminated, Educational information cards released for grower use
Aug 15, 03 OSU; Hort MagNet Mania Newsletter Release-Fall 03 issue 2 (alternative methods)
Sept 18, 03 Aurora OR Oregon Fresh Market Growers Association Meeting- Cabbage Maggot IPM Program- Canada and US Vegetable Production Talk and Proceedings
Feb 18-9, 04 Abbotsford BC Canada Invited speaker to 46th Annual Horticulture Growers’ Short Course-Pacific Agriculture Show. Topic Presented: Maggot IPM and presented a Mini-Workshop demonstrating use of laminated education cards as a valuable guidance tool (see evaluation forms)
Feb 16, 04 Corvallis OR Presentation: “How to Measure IPM Adoption-the PEST Plan.” A follow-up discussion involved:1. Development of IPM Guidelines for Oregon; 2. Measurement of IPM adoption; 3. Measurement of IPM impact and risk reduction; 4. Maximizing benefits to other agencies and partners (commodity groups, ODA, NRCS etc.)
Mar 7, 04 OSU; Hort MagNet Mania Newsletter Release-Spring 04 issue 3 (fungus use for maggot control)
Mar 16, 04 Corvallis OR Presented: “GPS-GIS IPM tool for Growers” Mini-Workshop demonstrating mapping and use of laminated educational IPM cards at Field Day Events
Mar 31, 04 NWREC, Canby OR “Where are we headed in the Maggot World”- Round Table Grower Discussion. Presented 2000-2003 data on: 1) phenology and CM life cycle on how this relates to planting dates, damage levels, and harvest period; 2) 12 trials explaining best application techniques, chemicals with increased efficacy, and new potential chemistries based on results; 3) spring cultivation trials.
Nov 2, 04 Canby OR Monitoring Training- Transfer of Technology to Scouts
and Vegetable Grower Workshop: Why monitor on the farm?
Nov 16, 04 Salt Lake City Utah Entomological Society of America Meetings.
Presented: Know thy Enemy: Strategies for managing the cabbage maggot, Delia radicum L.
Nov17, 04 Salt Lake City UT Co-Moderator for Root Maggot Symposium: Insights into Biology and Management of Root Maggot Pests
Jan 19-22, 05 Pacific Grove CA 25th Anniversary Ecological Farming Conference. Presented “Lifestyles of the Top 10 Beasts on the Farm”. Highlighted cabbage maggot IPM.
Mar 13, 05 Aurora OR Grower round table discussion regarding yearly MagNet IPM plan-on farm experiments
Apr 19-20, 05 Portland OR WCC-69 IPM Systems Tour- Highlighted Montecucco Farm and the MagNet Project. Discussed their pest management system; synthesized IPM practice use, system components and IPM behavior and limitations. IPPC Systems Workshop Proceedings.
May 19, 05 Corvallis OR OSU Horticulture Seminar Series. Presented “Are IPM tools making it to the field?”
June 22, 05 Aurora OR Oregon Fresh Market Growers Association Spring Meeting-Vegetable Production and Insect Management. Presented MagNet IPM project update.
July 29, 05 Corvallis OR OSU Mini-College Master Gardener Workshop: “Cabbage Maggots and other pests in Action”.
Aug 30, 05 Portland OR IPM Indicators Workshop (USDA, CREES, IPM Regions, EPA): Invited speaker to present: MagNet project and grantee’s perspective on grant reporting .
Aug 31, 05 OSU; Hort MagNet Mania Newsletter Release-Summer 05 issue 4 (Resistance).
Oct 15, 05 OSU; Hort MagNet Mania Newsletter Release-Fall 05 issue 5 (Degree-day modeling).
Nov 3, 05 Canby OR IPM recommendations to growers for cabbage maggot control
May 26, 06 OSU; Horticulture Seminar Phenology and monitoring of the cabbage maggot in Brassica root crops.
The cabbage maggot is a universal pest problem. The current research designed a sound monitoring plan, analyzed the need for spatial rotation and timely planting and harvesting schedules, and explored a multiple array of seasonal tools such as sanitation, cultivation at harvest, row covers, exclusion fences, and trap crops that can be used to greatly decrease the use of pesticides. The current results also further documented that seed treatments, in-furrow applications, and timing of treatments at optimal egg-laying and high-risk periods (predicted by the degree-day model) can greatly reduce numbers of pesticide applications and environmental concern. In addition, the “PEST Plan” rating template serves as a model for measuring this impact, adoption, and success of a project. The plan provides an educational opportunity to reinforce the numerous tools of choice thus increasing adoption. Now all the grower has to do is choose some tools and move forward!
The cabbage maggot is a universal pest problem. The impact of this IPM project is widespread throughout the Pacific Northwest and many other Brassica growing regions around the U.S. (Midwest, South, and Northeast areas). In addition, much of the information and tools developed by the project for management of CM could be utilized worldwide (Canada and European countries).
All 36 Oregon counties rely on agriculture as a significant part of the local economy. Oregon grows over 20,000 acres of Brassicas vegetables including turnips, rutabagas, radish, daikon, broccoli, cauliflower, brussels sprouts, kale, collards, and cabbage for fresh market, processed, and seed production, all valued at over $20 million per year (Burt, 2004). Within Oregon, there are over 100 Brassica growers that will benefit from the MagNet project. Extending beyond Oregon, almost 200,000 acres of broccoli and cauliflower alone are grown annually in the U.S. for fresh and processed markets with a value of 692 million recorded (NASS, 2002). California produces about 90% of broccoli and cauliflower grown in the U.S.; Arizona, New York, Texas, and Oregon also provide. New York ranks number one in the country in production of fresh cabbage, and number two in processing cabbage. Valued at over $231 million per year, cabbage and other crucifers rank second in economic importance among New York vegetables, valued over $62 million per year. Cabbage maggot is worldwide, so will benefit from the MagNet project’s efforts in managing cabbage maggots implementing the IPM approach.
Over 41% of broccoli acreage, 31% cauliflower, and 100% of root crop acreage are prophylactically treated with chlorpyrifos to control CM (Quarles, 2000). The Brassica industry will benefit tremendously from the valuable inputs from the wide range of research and alternative development tools provided by this project. While we have been conducting much of the work on root crops, our findings will be directly applicable to all Brassica crops. In addition, the findings may also be applicable to closely related fly species with similar phenologies such as seed corn maggot (Delia platura), onion maggot (Delia antigua), and the carrot rust fly (Psila rosae).
If monitoring, preventative and the cultural practices are implemented then less pesticides will be used. Spatial separation (1/4 mile) of fall-planted from spring-planted cruciferous fields could dramatically reduce damage levels in the spring. Also, implementing timely planting and harvesting schedules could reduce maggot damage dramatically. Monitoring is key! A grower could reduce chemical input by at least 1/3 (conservatively) if monitoring and spatial and temporal practices were implemented and in some cases ½ when field plantings are grown during the lower risk windows.
U.S. Growers use over 4.6 million-acre treatments of organophosphates (and carbamate) pesticides annually, which represent 15% of pesticides used on vegetable crops (USEPA 2004). Because of its extensive use, chlorpyrifos metabolites have been found in the urine 82% of adults sampled from the National Health and Nutrition Examination Survey (2000), while the Minnesota Children’s Exposure Study found that 92% of 89 children evaluated had measurable urinary concentrations of 3,5,6-TCP, the primary urinary metabolite of chlorpyrifos. Adverse effects also have been seen as reproductive effects, neurotoxicity, sensitizer and irritant problems, birth defects, and toxicity to birds, fish, and aquatic organisms, and bees. By implementing monitoring and other cultural practices, we predict chemicals can be reduced by half.
Interrupting successive seasonal plantings of fields adjacent to one another, when high damage is observed at the first planting.
One of the pilot farms hired for the first time a scout for 18 months to help establish and implement over the last 12 months to monitor fields for pests. If better scouting and forecasting methods are implemented than less pesticide will be used.
Over the last 5 years working with the MagNet team of extension, researchers, and growers, IPM education through conversation, field experiments, and hands-on workshops has heightened grower self-analysis, awareness, confidence, and knowledge base. They now are seeing the available IPM tools for control of cabbage maggots and have better evidence that IPM techniques can work. This is the first step for change. We were highly impressed when one of the top acreage growers hired a monitoring scout for the first time to inspect fields for pests (insects, weeds, disease). This step was encouraging and crucial towards IPM adoption. Changes in IPM adoption behavior lead directly to changes in pesticide use patterns. The Brassica growers (approx. 100) are headed on the right path. Now we are entering Phase II in 2006 — technical transfer and grower support! Growers need encouragement and guidance in choosing the tools that will work for them.
There is a lot of pressure from the urban community to produce safer and lesser pesticide-applied vegetables. We continually inform and educate the encroaching urban community about grower practices and their attempt to reduce pesticide use by performing on-farm trials of alternative practices in the neighborhood. Many neighbors were curious and stopped us in the fields inquiring about the green emergence catches or yellow water buckets scattered around the fields. We eventually included a sign in some of the fields posting, “OSU-Grower Research testing New and Safer Practices for Control of Pests.” This was a good opportunity to share the IPM philosophy (acronym P.E.S.T = Prevention, Exclusion, Suppression, and Thoughtfulness principles (Dreves 1996)). Fellow farmers were also exposed to on-farm experiments performed by the 3 pilot growers through sharing at local meetings, outside talks, and the 6 workshops that everyone was invited to, making tool adoption more rapidly widespread once approved.
Three main pilot growers were involved in all stages of the MagNet project. Growers identified a problem, decided on a strategy (e.g., alternative chemistries, seed treatments, row covers, exclusion fences, etc.) to be tested, worked with us to implement the experiment, and participated in evaluating the results and conclusions. This helped us modify the tools and equipment to better suit the grower.
The fresh market association vegetable growers have worked very little with each other or with Cooperative Extension, a resource for alternative pest management strategies. Improved communication between growers is significant to future IPM advancement, if we plan to incorporate a regional Brassica rotation plan.
Areas needing additional study
Other areas in need of study to help contribute to an effective cabbage maggot management program include: Mapping and rotating fields, determining distance away from source of CM infestation to minimize damage, usefulness of trap cropping, selection of and timing for insecticide applications, effective application equipment, selective location spraying, efficient sequential sampling of oviposition and damage, implementation of tools, and grower support with IPM transition.