Final Report for LNC07-284

Project Type: Research and Education
Funds awarded in 2007: $129,427.00
Projected End Date: 12/31/2010
Region: North Central
State: Iowa
Project Coordinator:
Dr. Mark Gleason
Iowa State University
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Project Information

Summary:

This 3-year systems-level project showed that scab resistant varieties, a disease-warning system, and mulching can enhance sustainability of Iowa apple orchards. Combining scab-resistant varieties with a warning system for sooty blotch and flyspeck disease resulted in fewer pesticide sprays and spray trips, lower pest management costs, and sharply reduced environmental impact compared to either calendar-based spray timing or a standard IPM program, with equivalent yield and fruit quality. Mulching with composted hardwood bark mulch reduced reliance on chemical herbicides and resulted in soil that was cooler, moister, and higher in organic matter than in bare-ground plots. The project also showed that high-quality hard cider can be produced from Iowa apples, including scab-resistant varieties, as a value-added product for apple growers. Results were shared with Iowa growers through field days and annual research reports.

Introduction:

Commercial apple orchards in the North Central Region face serious challenges to sustainability: shrinking profit margins, loss of mainstay pesticides, and the demise of key IPM programs.

Midwest growers suffer competitive disadvantages because diseases, insect pests, and weed pressure far exceed those of major competitors: Washington State, Chile, and New Zealand. Therefore, growers need to carve out specialized niches – such as unique varieties and value-added products – that are a good fit for Midwest conditions.

IPM strategies against apple scab, the number one apple disease, have collapsed following proliferation of fungicide resistance by the scab pathogen. The result is that Midwest growers must now return to calendar-based fungicide spray timing – almost the same as a generation ago – with many more sprays required. A shift to apple varieties which are highly resistant to apple scab could help to overcome this problem.

In 2006, EPA announced a phase-out of Guthion, the most widely used organophosphate (OP) insecticide for codling moth (the number one insect pest of apple) and greatly increased restrictions on use of Imidan, the other popular OP. New, lower-risk strategies are needed against codling moth.

Sooty blotch and flyspeck (SBFS), a disease caused by a complex of fungi, is the main reason Midwest growers apply 4 to 6 fungicide sprays in the summer. Disease-warning systems for SBFS allow growers to save some of these sprays, but need to be fine-tuned to be used reliably in the Midwest.

Conventional herbicides are often used to suppress weeds in tree rows, but the resulting bare soils can degrade soil quality and increase erosion. Grasses within rows hold the soil but competition for water can stunt apple trees. Organic mulches have been proposed as alternatives to overcome these problems, but have not been evaluated in the Midwest.

Hard cider offers an opportunity for adding value to apples, but few North Central Region growers currently produce this fermented product. However, hard cider could develop into a value-added and agri-tourism opportunity. Research is needed on how to produce a consistently high-quality product that appeals to Midwest consumers.
Our project attempted to meet these pest-management and value-added needs in an integrated 3-year project based in Iowa.

Project Objectives:

Objective 1: Compare innovative practices to conventional IPM and traditional practices for disease, insect, and weed management in annual field trials.

Objective 2: Develop methods for producing hard apple cider of consistently high quality that Midwest consumers are willing to buy.

Objective 3: a) Calculate the costs, benefits, and risks of the alternative apple management systems in Objective 1; b) Estimate the costs, benefits, and risks associated with local-scale manufacturing and marketing of hard cider in Iowa.

Objective 4: Communicate project findings to North Central Region apple growers through on-farm demonstration trials, field days, meeting presentations, statewide and regional newsletter and trade-journal articles, a project website, press releases, and an on-line Extension bulletin.

Performance targets for research, stated in the project proposal: field validation of best management practices that integrate current disease, insect pest, and weed management innovations with disease-resistant apple varieties; cost-benefit and environmental impact analyses of each strategy; hard cider production methods that produce a superior product; and refereed publications in technical journals. Outreach targets included: three field days; nine presentations at regional grower meetings; articles in Fruit Growers News; a project website; and an on-line extension bulletin

Research

Materials and methods:

OBJECTIVE 1 – Field trials

This Objective included two field trials: Trial 1 integrated IPM strategies on disease-resistant varieties, and Trial 2 assessed the impact of spray volume and pruning on performance of a warning system for sooty blotch and flyspeck disease (SBFS).

Trial 1

The location was a producing 1-acre orchard at ISU Horticulture Farm, Gilbert, IA, with scab-resistant apple varieties Redfree (early season), Liberty (mid-season), and Gold Rush (late season) on M9 rootstock. Experimental design was a randomized complete block with 4 treatments: 1, traditional calendar-based timing of fungicide and insecticide sprays; conventional IPM (no accounting for scab resistance of the cultivars, but degree-day-based timing of insecticides); 3, New IPM A (SBFS warning system based on cumulative leaf wetness duration; weekly sprays of granulosis virus for codling moth); and 4, New IPM B (SBFS warning system based on cumulative hours of relative humidity above 97%; granulovirus sprays timed with degree day model and alternated with the low-risk conventional insecticides novaluron and thiacloprid. Measurements included hourly wetness duration and temperature (Wetness/Temperature Loggers; Spectrum Inc.); incidence of scab, SBFS, other diseases, and injury by arthropod pests at harvest; and number and size of each weed species in 0.5 m2 quadrats per subplot every 6 weeks during the growing season. Yield was separated into marketable and cull grades; marketable apples were graded by size, counted, and weighed. Tree height, trunk caliper, and cross-sectional area were measured annually.

Results for each treatment were assessed annually on a rating scale called the Field Environmental Impact Quotient (FEIQ), indicating ecological risks. The point value for each pesticide is proportionate to the ecological risk associated with its use. Total risk for each treatment was determined for each cultivar using the sum of FEIQs for each pesticide. FEIQ for each pesticide was determined by the following equation: (EIQ) x (percent active ingredient) x (dose/hectare) x (number of applications). Cydia pomonella granulovirus was not assigned a rating in previous studies, so an EIQ value (6.7) was developed based the same parameters used by Kovach et al.

In addition to the treatments applied to the orchard canopy (above) mulching was compared to a bare-ground control. There were five paired replications (five-tree row segments of the same cultivar) per treatment; within each pair, the same cultivar was used for mulching and bare-ground subplots. Mulched subplots received a 15-cm-deep layer of composted hardwood mulch in a 2-m-wide strip beneath the tree canopy in June 2006 and June 2008. A 30-cm-wide zone around tree trunks was maintained mulch-free. Two-meter-wide strips beneath the canopy were maintained free of weeds from the beginning of May until the beginning of July. An initial herbicide application was made at the beginning of each season to both bare-ground and mulched subplots. Herbicide sprays were applied using a boom sprayer when the tallest weeds had reached 12.5 cm in height. After mid-July, weeds were controlled primarily by periodic mowing. In 2007 and 2008, soil temperature was measured at 5-and 10-cm depths in one subplot of each bare-ground and mulched soil treatment using thermistors (Model 107, Campbell Scientific, Logan, UT). Soil volumetric water content was measured at 15- and 30-cm depths using time domain reflectrometry (TDR) sensors (Model CS616, Campbell Scientific). Before bud break in 2007 and 2008, growth was assessed for the center three trees in each subplot. Trunk diameter was measured 15 cm above the graft union. Tree height and limb spread from north to south were recorded before bud break in mid-March of 2007 and 2008 using a measuring tape. Weed species data were collected monthly from May to September of 2007 and 2008 along 13 transects per subplot, yielding 130 data points per subplot. At each point, presence or absence of weeds was noted; if present, the tallest weed was identified to species. Weed biomass was assessed annually in early September, using a 0.1 m2 quadrat that was placed randomly at five locations in each subplot. Weeds harvested from five subsamples in each subplot were combined, oven-dried for 3 days at 65° C, and weighed.

Trial 2

The plot was a 0.5-acre block of cv. Chieftain on M7 rootstock, planted in 1987 at ISU Hort Farm. Experimental design was a RCB with 8 treatments (2 pruning x 4 fungicide-spray treatments). Subplots (3- to 4-tree row segments) were either pruned the previous winter or not pruned, and were sprayed at a rate of 48, 100, or 200 gallons per acre for the first-cover and second-cover fungicide sprays. After the second-cover spray, additional fungicide sprays were applied every 2 weeks until harvest at 48 gal/acre. Non-sprayed control treatments (no fungicide sprays after petal fall) were either pruned or not pruned. Insecticides were applied to the entire plot on calendar-timed basis.

Measurements included incidence of SBFS (% apples with SBFS signs) on 50 apples per tree at harvest, as well as incidence of damage from other diseases and insects.

OBJECTIVE 2 – Hard cider production trials

Apples were pressed for cider production in November 2006 and 2007, and January 2009, from apples that had been grown in 2006, 2007, and 2008 respectively. Varieties Liberty and GoldRush was harvested from the Leopold Center field trial at the Hort Farm. Varieties Golden Delicious, Jonathan, Chieftain, and MacIntosh were grown in other blocks at the Hort Farm under conventional management, and ‘Fireside’ was purchased from a local commercial orchard (Storybook Orchard, Story City, IA).

Varieties used for hard cider production were grown in each year of the project as follows: 2006, Golden Delicious, Fireside, Liberty, and GoldRush; 2007, Golden Delicious, Jonathan, Chieftain, and MacIntosh; 2008, Golden Delicious, Jonathan, Fireside, Chieftain, MacIntosh, GoldRush, and Liberty. Grinding, pressing, fermentation and bottling took place at the ISU Center for Crops Utilization Research (CCUR).

Apples from the ISU Hort Farm and other orchards were harvested, sorted, and washed prior to processing into identify preserved juices. Each juice was manufactured in the CCUR Pilot Plant at ISU using standard methods and equipment. Apples were sorted, washed, weighed, ground and pressed in a Day Equipment Company Cider Press system. The juice was filtered through standard cider press cloths, and pressed by hydrolytic pressure. The juice was collected in stainless steel milk cans, weighed, placed in fermentation vessels with gas-locks, and analyzed for pH, acid (titratable acidity), and sugar content. Additional sugar was added, as necessary, to allow for appropriate alcohol production, and champagne yeast was added to ferment the cider. The fermentation was stopped at the desired alcohol content by refrigerating the fermenters. The fermentation was followed by pulling samples using a sterile sampling thief. After fermentation to specific endpoints based upon commercial hard ciders, the wine was racked, bright filtered, labeled, and stored refrigerated for 2 months. Prior to sensory panel evaluation, the wines were standardized to 80 Brix and bottled in green glass screw-capped wine bottles. Blends were produced from the various cultivars, and initially evaluated by a volunteer panel and members of the Midwest Wine and Grape Institute, based upon the number of blends that the sensory panel needed. The best blends were reproduced and stored until needed.

Varietals and blends were evaluated for apple aroma, color, taste (sweet, sour, bitter), flavor, and mouthfeel. All varietal and blend hard ciders were analyzed for sugar, titratable acidity (% malic acid), sugar/acid ratio (brix/titratable acidity), pH, and alcohol content. All bottles of hard ciders were kept refrigerated until needed for sensory panel evaluation. When possible, the same cultivars and blends were made across all three years. Due to impact of weather conditions on apple availability, only year 3 contained all cultivars. Cider yield was determined for each crop year, and any remaining hard cider was stored for 1 year to determine its stability. Only year one cultivars, especially Liberty, threw pectin gels during storage. Pectinase treatment prevented this problem.

Sensory evaluation of hard ciders was conducted by Dr. Cheryll Reitmeier, ISU Department of Food Science and Human Nutrition (FSHN). Trained sensory panels consisted of 10 to 11 members per year, selected from students and faculty in FSHN. Panelists attended 3 one-hour training sessions to become familiar with the characteristics of apple cider, apple juice and hard ciders. They evaluated attributes of commercial hard ciders K, Woodpecker, Hardcore, Hornsby’s, Woodchuck, Strongbow, and Sutliff (Sutliff Winery, Solon, IA). Blends from the 2008 ISU study were also used for training.

Panelists determined the following characteristics for use on a 15-cm linescale from 0 = none to 15= intense: apple aroma, fermented aroma, effervescence, color, cloudiness, sweetness, sourness, and apple flavor. Each characteristic was compared to a reference exhibiting this characteristic.

After training, panelists evaluated the ciders on 4 separate days (sessions) in separate booths under fluorescent lights in the Human Nutritional Sciences Bldg, ISU. A completely randomized design was used to evaluate 7 cultivars and 3 replications. The 7 treatments and 3 replications were numbered 1-21 and randomly assigned to the 4 sessions. Panelists evaluated 5 samples at sessions 1-3 and 6 samples at session 4. Each panelist received the same set for each session.

Single-cultivar ciders were evaluated in 2007 and 2008. In addition, blends of selected cultivars were made in 2009 by Dr. Wilson. Blends were: Jonathan/Golden Delicious 50/50, Golden Delicious/MacIntosh 75/25, MacIntosh/Fireside 50/50, and MacIntosh/Jonathan 50/50. Panelists evaluated the blended ciders in 3 sessions (3 replications) in a complete block design.

Physical measurement data was analyzed by analysis of variance (MS Excel) and least significant difference (LSD) was calculated to determine means separation. Data from evaluation of the ciders were evaluated by analysis of variance. LSDs were calculated to determine means separation. Sensory evaluation data of blends were analyzed by analysis of variance and Tukey’s HSD multiple comparison test was used to determine means separation.

Soluble solids of the ciders were measured by using a Reichert AR200 Digital Handheld Refractometer. A HunterLab MiniScan® XE Plus was used to determine the color of each sample. Each sample was measured twice and means were calculated.

Ten to 11 panelists compared commercial cider and hard cider samples during training in December 2007, February 2008, and April 2009. They agreed that hard apple cider was described by the attributes apple aroma, fermented aroma, color, cloudiness, effervescence, sweetness, sourness and apple flavor. Standards for the maximum intensity of each attribute were determined: chopped raw Braeburn apple for apple aroma, Woodchuck® draft apple cider for fermented aroma, burnt sugar flavoring for color, Deal’s apple cider for cloudiness and apple flavor, Meier’s® sparkling apple juice for effervescence, 16% sucrose solution for sweetness, and 0.15% citric and malic acids for sourness.

OBJECTIVE 3 – Economic analysis of field trials

A partial budget, calculated from results of the canopy pest trials in 2008, was used to compare the cost and revenue of pest management strategies (26). To assess possible economies of scale, partial budgets were projected for orchard sizes of 0.4, 2.0, 4.0, 8.1, and 16.2 ha (16). In 2007, only treatment costs were determined due to frost-incited reduction of the crop in that year. Tractor and sprayer prices were estimated using an enterprise budget for medium density orchards. Machinery costs per hour reflected both variable and fixed costs. Variable costs included fuel, lubrication, and repairs and maintenance. Fixed costs included depreciation, interest, and insurance. A new four-wheel drive, 70 horsepower tractor cost $31.58 per hour. A new 400-gallon, power takeoff driven airblast sprayer cost $23.44 per hour. Total equipment cost was $66.02 per hour which includes an $11.00 per hour wage for a machinery operator (13). Fungicide and insecticide spray time was estimated at 20 minutes per 0.4 ha; spray preparation time was estimated to be 15 minutes, and clean-up was estimated as 30 minutes. Clean-up times were assumed to be the same for all orchard sizes. Weather-monitoring equipment was assumed to have a 5-yr lifetime, with an amortization rate of 20 percent. Although the number of required codling moth traps increased for larger orchards, only one datalogger was required for all orchard sizes examined. At harvest, the number of marketable and cull fruit were counted and weighed for trees in each treatment. Apples were graded and separated as <5.0, 5.0-6.3, 6.3-8.1, and >8.1 cm in diameter. Yield data were recorded from the middle three trees of each five-tree subplot in 2006 and 2008, and from all five trees per subplot in 2007. Returns of $3.31 per kilogram were assumed for all cultivars, based on a May 2008 telephone survey of prices which local Iowa growers said they received for fresh market apples. Price per kilogram was applied to average yield per tree in 2008. Average yield per tree was then multiplied by the number of trees per hectare (727). To calculate net returns, production costs (pesticides, machinery, monitoring equipment, spraying and scouting labor) were subtracted from the total fresh market value of fruit.

OBJECTIVE 4 – Outreach

Two sets of on-farm demonstration trials were conducted annually to evaluate ways to make a weather-based warning system for sooty blotch and flyspeck (SBFS) more practical and reliable for growers to use.

The first set of trials was aimed at pinpointing the lowest volume of fungicide spray (gallons per acre) that could safely be used when spray timing was dictated by the SBFS warning system. Lower spray volume is advantageous to a grower because one tank of spray covers more acres of orchard, reducing the need to interrupt spraying to refill the tank. However, low-volume spraying has also been identified in the past as a contributor to SBFS control failures. The on-farm trials compared medium-volume (80 or 100 gallons per acre) vs. low-volume (40 or 50 gallons per acre) fungicide sprays, applied at first and second cover, in operating the SBFS warning system, which requires a 175-hr threshold of cumulative hours of leaf wetness duration to occur between these two sprays. These trials were held at Community Orchard (Ft. Dodge, IA), Deal Orchard (Jefferson, IA), and Pella Nursery (Pella, IA). Each cooperator designated 10 trees of the same age and cultivar for use in the trial: 5 contiguous trees for use with the medium-volume sprays, and 5 for use with the low-volume sprays. Project scouts explained the trial to the cooperators, installed wetness sensors (Wetness/Temperature Logger, Spectrum Technologies, Plainfield, IL) in the trial area, and helped growers monitor cumulative wetness by downloading data on a weekly basis. Within a week before harvest, the scouts examined 50 arbitrarily selected apples per tree for incidence of SBFS signs.

The objective of the second set of annual on-farm trials was to validate the SBFS warning system, using a threshold of 175 cumulative hours of wetness between the first- and second-cover fungicide sprays, in six orchards: Deal Orchard; Pella Nursery; Community Orchard; Center Grove Orchard, Cambridge, IA; Apple Ridge Orchard, Iowa Falls, IA; and Berry Patch Farm, Nevada, IA. Cooperators were asked to implement the SBFS warning system for a small portion of their orchard (usually 10 or fewer trees of the same cultivar. Project scouts communicated with the growers, monitored hours of leaf wetness, and evaluated fruit for SBFS signs at harvest as described above. Growers used their customary spray volume for fungicide sprays in this trial.

Three field days featured progress reports and handouts about the SARE project. There were no field days in 2007, due to a severe freeze in early May of that year which wiped out most of Iowa’s apple crop. On June 25, 2008, the Iowa Fruit and Vegetable Growers Association (IFVGA) held their annual field day at Sutliff Winery in Solon, Iowa. The owner, Scott Ervin, demonstrated his techniques for fermenting, aging, carbonating, and bottling his commercial hard cider. Grower attendance was about 55. Project PI Paul Domoto answered questions from attendees. Second, a field day sponsored by the IFVGA was held at Bill Campbell’s orchard near Harlan, IA, on June 20, 2009. Mark Gleason presented information and a handout about the Leopold Center field experiment at the Hort Farm and the on-farm trials; attendance was 40 people. Third, during a field day at the ISU Hort Farm on August 5, 2009, intern Rachel Kreis gave a short in-field presentation on the SARE project and distributed a handout; attendance was 60 people.

At the annual IFVGA winter meeting in January 2008, project PI Gleason presented a talk on organic apple production that included explanation of the SARE project trials at the ISU Hort Farm.

Research results and discussion:

OBJECTIVE 1

Trial 1 – IPM systems for disease, insect pest, and weed management

For each treatment, pesticide spray trips were often fewer in number than individual pesticide sprays because fungicide and insecticide sprays that were required at nearly the same time on the same treatment blocks were tank mixed where feasible in order to conserve energy, fuel, and time. Averaged over all three cultivars and 3 years, Treatment 4 required the fewest pesticide sprays (14.3) and spray trips (10.6) of any treatment. In each year, cv. Redfree had the fewest insecticide and fungicide sprays, since it matured 5 and 9 weeks earlier than Liberty and GoldRush, respectively. In 2007, Treatments 1 (calendar-based spray timing), 2 (conventional IPM), and 3 (New IPM A) each required more pesticide sprays than Treatment 4 (New IPM B). Redfree was the least pesticide-intensive of the three cultivars, which suggests that it would also be the least expensive to grow (see Objective 3).

The period between first- and second-cover fungicide sprays varied from 14 days (calendar-based control and conventional IPM) to 34-60 days (Treatments 3 and 4), depending on year and the version of the SBFS warning system that was used. This increased time gap between fungicide sprays translated to a savings of 2 to 4 sprays per year. Interestingly, thresholds for timing of the second-cover fungicide spray were quite similar (2 to 10 days different, depending on year) for two alternative versions of the SBFS warning system – 175 hours of leaf wetness duration (Treatment 3), or 192 hours of relative humidity of 97% or more (Treatment 4).

In 2007, when few apples (and none of ‘Liberty’) were harvested due to a severe spring frost, marketable and cull apple weight and number did not differ significantly among treatments. In 2008, there was no difference among treatments in weight or number of marketable fruit weight, except in GoldRush, for which Treatment 2 had significantly less marketable weight than Treatments 1 or 4. In 2009, there were no treatment differences in marketable fruit weight; for GoldRush, however, number of marketable fruit for Treatment 4 was significantly higher than for Treatments 1 or 3.

No scab damage on fruit was evident during the study; this was expected due to each cultivar’s high level of genetic resistance to scab. Furthermore, no SBFS was ever observed on ‘Redfree’ apples; the reason was not inherent genetic resistance of ‘Redfree,’ but rather that its early maturity date enabled it to escape this disease. Even in unsprayed and organic orchards, cultivars that mature in early August, such as Redfree, exhibit little or no SBFS. For this reason, the most suitable apple cultivars for minimal-fungicide orchards or organic disease management in the North Central Region may be scab-resistant, early-maturing ones. On the other hand, early-maturing cultivars typically do not store well, so they must be marketed within 4 to 6 weeks after harvest. In addition, a local or regional market must be established for any cultivar that is new to consumers. Redfree has sold well for Iowa growers who have tried it, however, and could be a good addition to the cultivar mix in other NC Region orchards due to its minimal fungicide needs.

In 2007, there were no significant differences among treatments for incidence of codling moth, SBFS, or plum curculio. However, incidence levels of codling moth and plum curculio were above commercially acceptable thresholds, possibly due to the anomalous nature of the greatly reduced crop (a result of springtime frost), which may have resulted in focusing pests on just a few apples per plot rather than a normal-size crop. In 2008, no SBFS or plum curculio was observed on Redfree, codling moth damage was minimal, and incidence of SBFS was less than 1 % in all treatments. In 2009, incidence of SBFS, codling moth injury, and injury by other insects was less than 1% in all treatments, with one exception: injury by other insects was 1.6% on cv. Liberty in Treatment 4. These injury levels are all within commercially acceptable thresholds. The 2008 and 2009 results are clear evidence that the New IPM treatments (3 and 4) suppressed the targeted summertime diseases and pests (SBFS and codling moth) and non-target insect pests as effectively as either a traditional, calendar-timed pesticide spray schedule (Treatment 10 or a conventional IPM spray schedule (Treatment 2).

Using the Field Environmental Impact Quotient (EIQ) as a measure, the New IPM Treatments (3 and 4) had far less environmental risk than calendar-based spraying (Treatment 1) or conventional IPM (Treatment 2). In 2007, New IPM treatments has Field EIQ scores more than 40 % lower than calendar-based and more than 30 % lower than conventional IPM for cultivar ‘Redfree,’ while the New IPM treatments showed nearly 50 % less ecological risk than calendar-based spraying for cultivar ‘Goldrush.’ In 2008, in part because early-season spraying differed from 2007, Field EIQ values for New IPM B (Treatment 4) were less than one-third of the values for the calendar-based spray timing control (Treatment 1). Results from 2009 were similar, but some Field EIQ values were higher due to more pesticide applications in a wetter year. Overall, comparison of the Field EIQ and pest management results show convincingly that combining scab-resistant cultivars with new IPM strategies such as warning systems can dramatically reduce the environmental impact of pesticide spraying in the North Central Region without compromising effectiveness of pest and disease control.

Mulched plots required spot treatments of herbicide throughout the season to manage localized outbreaks of weeds, but bare-ground plots required herbicide applications over the entire ground surface. Across the 3 years, mulched plots required an average of 23.9% less herbicide than bare ground plots. In the early to mid-season, which are the most important time for weed competition with apple trees, weed coverage was significantly greater on bare ground than on mulch in each year (July and August 2007, May and July 2008, and July 2009), whereas weed coverage on bare ground was never less than on mulch. In midsummer, common purslane (Portulaca oleracea) covered nearly 50% of sampling points in bare-ground plots, whereas it was nearly absent from mulched plots. In contrast, barnyard grass (Echinochloa crus-galli) and large crabgrass (Digitaria sanguinalis) occasionally covered significantly more of the mulched than bare-ground plots. Weed suppression was more effective in the same year in which a mulch layer was applied (2006, in a preceding study on the same site) or re-applied (2008), and somewhat less effective in years following application of fresh mulch (2007 and 2009).

A key take-home message for growers is that composted hardwood bark mulch effectively suppressed weed growth on the orchard floor during the critical period of the growing season for competition with apple tree growth (May through July). This suppression would likely mean that apple trees that are mulched within the tree row would experience less weed competition for water and nutrients during dry growing seasons than under the bare-ground cultivation that is common in many North Central Region orchards. This advantage could be particularly important during orchard establishment, when it is critically important economically for young trees to reach full bearing size and fill the rows in as few years as possible.

In 2007 and 2008, average weekly soil temperatures beneath bare ground fluctuated considerably more than temperatures beneath mulched plots. Temperatures remained cooler under mulch, usually by at least 2° C, until late July, when the difference began to narrow. Volumetric water content beneath mulched plots at 15- and 30-cm depths was higher than under bare-ground plots throughout most of the season. The 2009 soil temperature and moisture content data were more equivocal due to problems with monitoring equipment.

The take-home message from these results is that, in well-drained soils such as at the ISU Hort Farm, the cooler and less variable soil temperatures and greater water availability resulting from mulching should help to minimize stress on root systems and maintain tree vigor during hot, dry periods. For the same reasons, however, mulching may not be as suitable for relatively poorly drained soils, where the mulch layer could potentially contribute to waterlogging, low-oxygen conditions, and resulting root injury during prolonged wet weather. Therefore, the suitability of composted hardwood bark mulching for apple orchards should be evaluated on a site-by-site basis.

Mean soil nutrient levels, organic matter, and pH varied widely among bare-ground and mulched plots in all three years. Total percent carbon, nitrogen, and organic matter were nearly identical between treatments in 2006, but in 2007 they all increased in mulched relative to bare-ground plots, and these differences were statistically significant in 2008. This finding suggests that decay of organic mulch can raise the organic matter content of soil and thereby yield benefits such as improved soil texture, structure, cation exchange capacity, and water-holding capacity. Again, however, this impact may be somewhat site-specific; the greatest benefit may accrue to soils that are relatively low in organic matter before mulching occurs; this would be true of many, but not all, agricultural soils in the North Central Region

In 2007 and 2008, means of foliar nutrients and foliar moisture content did not differ significantly between bare-ground and mulched plots. Trunk diameter, tree height, and limb spread did not differ significantly for trees in bare-ground and mulched plots in 2007, 2008, or 2009. In other words, there was no discernible impact of mulch in tree growth or nutrition. Two factors may explain this result. First, no droughts occurred during the entire period, and 2008 and 2009 growing seasons were exceptionally rainy. As a result, water for growth was not as relatively limiting on bare ground as it could have been during prolonged dry conditions. Second, the mulching treatments were applied across all three cultivars; the resulting variability may have obscured cultivar-specific growth differences between bare ground and mulched treatments.

Trial 2 – Impact of pruning and spray volume on performance of a SBFS warning system

Results from the 2007 ISU Hort Farm trial on cv. Chieftain revealed no significant differences among treatments; the near-total crop loss in that year (due to spring frost damage) resulted in very high variability in number of apples rated per subplot, and thereby contributed to high variability within treatments. In 2008 and 2009, however, results were consistent: when using the SBFS warning system, a high volume (200 gallons per acre) in the first- and second-cover fungicide sprays resulted in significantly lower incidence of SBFS at harvest than low-volume (48 gallons per acre) sprays. Using 100 gallons per acre for these two sprays resulted in an intermediate incidence of SBFS. These differences occurred for both pruned and non-pruned trees. The spray-volume results were similar to those in the on-farm demonstration trials (see below), in which average SBFS incidence when using the warning system was lower when spray volume was 80 to 100 gallons rather than 40 to 50 gallons.

Pruning appeared to have less impact than spray volume. In 2008, for example, the non-pruned, non-sprayed control did not differ significantly from the pruned, sprayed control in SBFS incidence, whereas in 2009 the non-pruned, non-sprayed control had significantly lower SBFS incidence than the pruned, non-sprayed control.

The take-home message for North Central Region growers is that it is more reliable to use the SBFS warning system with spray volume of at least 100 gallons per acre than at lower volumes (e.g., 40 to 50 gallons per acre). The results have practical value for growers by clarifying a basic rule of thumb (minimum spray volume for first- and second-cover fungicide sprays) necessary for reliable use of the SBFS warning system. Although annual dormant-season pruning may have less impact on warning-system performance than spray volume, pruning is still strongly recommended to insure adequate light penetration, remove dead wood than can contribute to certain diseases, and provide needed shaping of developing trees.

OBJECTIVE 2 – Hard cider trials

No statistical differences in hard cider quality characteristics were noted in 2007, 2008, or 2009, presumably due to variability from year to year, comparison of different cultivars each year, and the fact that only two replications were completed for all cultivars. Golden Delicious was the only cultivar evaluated in each year, and had three replications per evaluation. Although no statistical differences were noted, hard cider made from Jonathan, Fireside, Chieftan, MacIntosh, and Golden Delicious apples tended to be rated higher in aroma, sweetness, and apple flavor and lower in sourness than cider from Gold Rush and Liberty apples. It should be noted, however, that fermented aroma, effervescence and cloudiness can be altered in processing. Sweetness and sourness can be adjusted with addition of sugar or by blending with other juices, and coloring agents could be added.

In comparing our ciders with commercial brands, ISU hard ciders were most similar to the commercial brand “K”, made by Matthew Clark Brands, Bristol, England. Commercial hard ciders made in the U.S. were darker yellow-amber in color and more effervescent, with less apple flavor, than ISU ciders. Blends were made with traditional, widely grown cultivars (Jonathan, Golden Delicious, MacIntosh) and Fireside. Fireside was similar to other cultivars in several attributes and may be a suitable apple for cider; however, hard cider made from Fireside apples tended to be lower in apple flavor than other apple cultivars.

OBJECTIVE 3 – Economic analysis

Costs and revenue were not calculated for 2007, because a killing frost eliminated more than 95% of the fruit in the plot, including 100% of the Liberty apples. In 2009, pest management costs were somewhat higher than in 2008 across all cultivars because wetter weather required several more pesticide sprays.

For all treatments in both 2008 and 2009, per-hectare costs were lower and revenue was higher as orchard size increased from 0.4 hectare (1 acre) 16.2 hectares (40 acres). Cost of pest management was highest for Treatment 3 at all orchard sizes because weekly sprays of Cyd-X (codling moth granulosis virus) required substantially more spray trips than the other treatments. Cost for Treatment 4 was the lowest of all treatments at orchard sizes of 2 hectares (5 acres) and larger.

Cost savings for Treatment 4 (New IPM using the SBFS warning system and two fewer springtime fungicide sprays against scab) compared to Treatment 1 (Traditional calendar-based pesticides spray timing) varied with cultivar and year. For an 8.1-hectare (20-acre) orchard, for example, annual per-orchard cost savings for fungicides and insecticides in Treatment 4, compared to Treatment 1, ranged from $300 (cv. Redfree in 2008) to $510 (cv. Liberty in 2008). When comparing Treatment 3 (Conventional IPM without SBFS warning system or reduced scab sprays) with Treatment 4, annual per-orchard savings ranges from $324 (cv. Goldrush in 2009) to $348 (cvs. Liberty and Goldrush in 2008). These cost savings from using Treatment 4 did not compromise yield or fruit quality compared to the controls (Treatments 1 or 2). While the cost savings from Treatment 4 are not massive, they can strengthen a farm’s balance sheet. At the same time, reducing the pesticide load and substituting lower-toxicity products can substantially reduce the environmental impact of spraying (see Field EIQ results), thereby enhancing populations of beneficial arthropods and reducing pesticide contamination of the orchard soil community, groundwater, and nearby surface waters.

OBJECTIVE 4 – Outreach

In 2007, results of on-farm demonstration trials were compromised by a spring frost that drastically reduced the apple crop in all cooperator orchards, as well as a miscommunication that resulted in the project scout’s failure to take data on incidence of SBFS on apples at harvest at the three cooperator orchards.

In 2008 and 2009, on-farm, non-replicated trials included three cooperators in each year, for a total of six site years. In the trials evaluating the SBFS warning system with a threshold of 175 hours of cumulative leaf wetness duration, use of the warning system resulted in a 10% average incidence (% apples infected) of SBFS compared to 3% in the control (calendar-based spraying). Although the results were highly variable among cooperators, the higher level of SBFS with the warning system suggests that the leaf-wetness-based warning system may need to be re-evaluated. In fact, a new warning system, based on cumulative hours of relative humidity greater than 97%, was field-validated in Objective 1. This new system performed well in the Hort Farm trial, but needs to be validated over additional sites and years before it is sufficiently reliable for growers to use.

Also in 2008 and 2009, the impact of spray volume on performance of the warning system (with the 175-hour cumulative leaf wetness threshold) was tested in three commercial orchards. Incidence of SBFS at harvest varied widely among the six site years, so differences among orchards and across site years were not statistically significant, but several trends emerged. The highest average SBFS incidence (8.8%) occurred when the warning system was used in conjunction with low-volume gallonage (i.e., 40 to 50 gallons per acre) for the first- and second-cover fungicide sprays. In contrast, SBFS incidence was lower (6.3%) when the warning system was applied using higher spray volume (80 to 100 gallons per acre). The lowest average incidence of SBFS, 3.7%, occurred when low-volume fungicide sprays were applied on a calendar basis. These results suggest that spray volume does make a difference in controlling SBFS when using the warning system; 80 to 100 gallons outperformed 40 to 50 gallons. At 80 to 100 gallons per acre, however, a sprayer would need to be refilled twice as often as at 40 to 50 gallons per acre, so labor, fuel costs, and overall spray time required would be somewhat greater for the higher volume. However, data presented in this report and elsewhere indicate that the SBFS warning system can cut the number of fungicide sprays for North Central Regions growers by at least two per season, resulting in cost and time savings that are considerably greater than the added costs of refilling a spray tank a few more times. However, the fact that the calendar-timed fungicide spray schedule resulted in an even lower incidence of SBFS than the warning system with higher spray volume suggests that the warning system needs to be further refined in additional field trials, and also that it would be valuable to try applying the warning system with spray volumes exceeding 80 to 100 gallons.

Research conclusions:

Our 3-year ISU Horticulture Farm study was the first systems-level assessment of the impact of scab-resistant cultivars on apple orchard sustainability in the North Central Region. By eliminating several springtime sprays for scab and implementing weather-based spray timing for the primary summer pest problems (sooty blotch/flyspeck and codling moth), we demonstrated that apple growers can dramatically reduce the environmental impact of pest and weed management, save money, and safeguard the quality and yield of their apples. We also showed that using composted hardwood bark mulch in the tree-row strip can suppress weeds, reduce the need for herbicide sprays, create a cooler and moister rooting environment, and enhance the organic matter content of the soil. The pruning and spray volume experiment and on-farm trials pointed to adequate spray volume

The greatest impact of our field experiment and on-farm trials is likely to be as a source of ideas for Midwest apple growers who are looking to cut production costs while reducing their orchard’s environmental footprint.

The project’s progress has been shared mostly with Iowa apple growers so far, via three field days and publication of annual summaries in the Iowa State University Fruit and Vegetable Progress Report. Publications summarizing the project are also in preparation for submission to the Iowa Fruit and Vegetable Growers newsletter, Midwest grower journal Fruit Growers News and the national research journal Agriculture, Ecosystems, and Environment by the end of 2010.

Economic Analysis

Costs and revenue were not calculated for 2007, because a killing frost eliminated more than 95% of the fruit in the plot, including 100% of the Liberty apples. In 2009, pest management costs were somewhat higher than in 2008 across all cultivars because wetter weather required several more pesticide sprays.

For all treatments in both 2008 and 2009, per-hectare costs were lower and revenue was higher as orchard size increased from 0.4 hectare (1 acre) 16.2 hectares (40 acres). Cost of pest management was highest for Treatment 3 at all orchard sizes because weekly sprays of Cyd-X (codling moth granulosis virus) required substantially more spray trips than the other treatments. Cost for Treatment 4 was the lowest of all treatments at orchard sizes of 2 hectares (5 acres) and larger.

Cost savings for Treatment 4 (New IPM using the SBFS warning system and two fewer springtime fungicide sprays against scab) compared to Treatment 1 (Traditional calendar-based pesticides spray timing) varied with cultivar and year. For an 8.1-hectare (20-acre) orchard, for example, annual per-orchard cost savings for fungicides and insecticides in Treatment 4, compared to Treatment 1, ranged from $300 (cv. Redfree in 2008) to $510 (cv. Liberty in 2008). When comparing Treatment 3 (Conventional IPM without SBFS warning system or reduced scab sprays) with Treatment 4, annual per-orchard savings ranges from $324 (cv. Goldrush in 2009) to $348 (cvs. Liberty and Goldrush in 2008). These cost savings from using Treatment 4 did not compromise yield or fruit quality compared to the controls (Treatments 1 or 2). While the cost savings from Treatment 4 are not massive, they can strengthen a farm’s balance sheet. At the same time, reducing the pesticide load and substituting lower-toxicity products can substantially reduce the environmental impact of spraying (see Field EIQ results), thereby enhancing populations of beneficial arthropods and reducing pesticide contamination of the orchard soil community, groundwater, and nearby surface waters.

Farmer Adoption

Adoption of the management options tested in this project by apple growers in the North Central Region depends on the specific option. Many growers with local markets have experimented with scab-resistant apple cultivars over the past 30 years, and some of the most popular niche cultivars are the ones we studied in this project: Redfree, Liberty, and Goldrush. These apples have found devoted consumers for on-farm sales and farmers markets. However, they have not penetrated supermarket sales to a meaningful extent, primarily because of a lack of marketing effort by the apple industry or supermarket chains. Apples sold in supermarkets are mostly either familiar mainstays or new varieties that have been actively promoted by the apple industry (especially the Washington State industry). It is therefore likely that scab-resistant varieties, which were mostly released during the past 20-25 years, will remain niche varieties in the Midwest. However, the proliferation of scab resistance to DMI fungicides is likely to add to grower incentives to try scab-resistant varieties in new plantings, as a more economical way to manage this ubiquitous disease. Our project makes clear that there are both economic and environmental advantages to growing scab-resistant apple varieties.

Our project’s findings make it more practical for Midwest growers to use a weather-based warning system to time fungicide sprays for control of sooty blotch and flyspeck (SBFS). If scab is controlled in the spring, SBFS is often the sole reason to apply fungicide sprays in the Upper Midwest (Iowa, Wisconsin, southern Michigan and Minnesota, and northern Illinois and Indiana). Using the warning system has been shown to reduce summertime fungicide sprays by 2 to 3 per season while protecting the crop against SBFS. Our project helped to add confidence for using the system by revealing that spray volume – in the first- and second-cover sprays – makes a difference in performance of the warning system. The recommendation coming from our upcoming publications is that growers should use at least 100 gallons of spray per acre for these two sprays in order for the warning system to control SBFS effectively. This new “rule of thumb” is important because it clearly adds to the reliability of this IPM strategy.

The attractiveness of mulching as a weed management and soil conservation strategy is likely to depend partly on soil type and climate. For well drained soils in climates that are drought-prone, our results show that composted hardwood bark mulch is likely to insulate apple trees from drought and heat stress – particularly in the critical early years when the trees are filling the row space and beginning to bear, and in orchards that do not irrigate. In our project, mulching provided significant weed deterrence, which could be particularly advantageous in organic orchards due to the lack of other cost-effective weed management methods.

The hard cider results showed that it is feasible to produce high-quality hard cider from Iowa-grown apples, including scab-resistant varieties. A grower workshop planned for January 2010 at Iowa State University, organized by the project PIs, will help growers from Iowa and surrounding states to gain a better understanding of how to produce and market hard cider.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Published:
Sisson, A.J. 2009. New integrated pest management for disease-resistant apple in the Midwest, and phenology of sooty blotch and flyspeck on apples in Iowa. M.S. Thesis, Department of Plant Pathology, Iowa State University, May 2009.

Gleason, M.L., Sisson, A.J., and Batzer, J.C. 2008. Assessing new methods of Integrated Pest Management for apple orchards in the Midwest, 2007. Annual Fruit and Vegetable Progress Report, Iowa State University.

Tatalovic, N., Gleason, M.L., and Batzer, J.C. 2008. Putting a sooty blotch-flyspeck warning system into practice, 2007. Annual Fruit and Vegetable Progress Report, Iowa State University.

Sisson, A.J. 2009. Evaluating effectiveness of a sooty blotch and flyspeck warning system at three commercial orchards in central Iowa – 2008. Annual Fruit and Vegetable Progress Report, Iowa State University.

Sisson, A.J., Gleason, M.L., and Batzer, J.C. 2009. Evaluating the impact of spray volume on effectiveness of the sooty blotch and flyspeck warning system at three commercial orchards in central Iowa – summer 2008. Annual Fruit and Vegetable Progress Report, Iowa State University.

Tatalovic, N., Batzer, J.C., and Gleason, M.L. 2009. Influence of spray volume and pruning on effectiveness of a sooty blotch and flyspeck warning system on apples, 2008. Annual Fruit and Vegetable Progress Report, Iowa State University.

Gleason, M.L., Sisson, A.J., and Batzer, J.C. 2009. Assessing new methods of Integrated Pest Management for apple orchards in the Midwest, 2009. Annual Fruit and Vegetable Progress Report, Iowa State University.

Penick, K., Gleason, M.L., amd Batzer, J.C. 2010. Evaluating the impact of spray volume on effectiveness of the sooty blotch and flyspeck warning system at three commercial orchards in central Iowa – 2009. Annual Fruit and Vegetable Progress Report, Iowa State University.

Gleason, M.L., and Batzer, J.C. 2010. Evaluating the impact of spray volume and pruning on effectiveness of a sooty blotch and flyspeck warning system, 2009. Annual Fruit and Vegetable Progress Report, Iowa State University.

Gleason, M.L., Sisson, A.J., Kreis, R., and Batzer, J.C. 2010. Assessing new methods of Integrated Pest Management for apple orchards in the Midwest, 2009. Annual Fruit and Vegetable Progress Report, Iowa State University.

In preparation:
Sisson, A.J., Gleason, M.L., and Batzer, J.C. A systems approach to management of scab-resistant apples in Iowa. Agriculture, Ecosystems, and Environment. Target for submission: November 2010.

Gleason, M.L., Batzer, J.C., and McManus, P.S. Impact of spray volume and pruning on performance of a warning system for sooty blotch and flyspeck in Iowa and Wisconsin. Plant Health Progress. Target for submission: October 2010.

Reitmeier, C.A., Wilson, L.A., and Gleason, M.L. Quality assessment of hard apple cider produced from Iowa apples. Journal of Food Technology. Target for submission: October 2010.

Outreach

(NOTE: Outreach also included under Objective 4 above)
In 2007, results of on-farm demonstration trials were compromised by a spring frost that drastically reduced the apple crop in all cooperator orchards, as well as a miscommunication that resulted in the project scout’s failure to take data on incidence of SBFS on apples at harvest at the three cooperator orchards.

In 2008 and 2009, on-farm, non-replicated trials included three cooperators in each year, for a total of six site years. In the trials evaluating the SBFS warning system with a threshold of 175 hours of cumulative leaf wetness duration, use of the warning system resulted in a 10% average incidence (% apples infected) of SBFS compared to 3% in the control (calendar-based spraying). Although the results were highly variable among cooperators, the higher level of SBFS with the warning system suggests that the leaf-wetness-based warning system may need to be re-evaluated. In fact, a new warning system, based on cumulative hours of relative humidity greater than 97%, was field-validated in Objective 1. This new system performed well in the Hort Farm trial, but needs to be validated over additional sites and years before it is sufficiently reliable for growers to use.

Also in 2008 and 2009, the impact of spray volume on performance of the warning system (with the 175-hour cumulative leaf wetness threshold) was tested in three commercial orchards. Incidence of SBFS at harvest varied widely among the six site years, so differences among orchards and across site years were not statistically significant, but several trends emerged. The highest average SBFS incidence (8.8%) occurred when the warning system was used in conjunction with low-volume gallonage (i.e., 40 to 50 gallons per acre) for the first- and second-cover fungicide sprays. In contrast, SBFS incidence was lower (6.3%) when the warning system was applied using higher spray volume (80 to 100 gallons per acre). The lowest average incidence of SBFS, 3.7%, occurred when low-volume fungicide sprays were applied on a calendar basis. These results suggest that spray volume does make a difference in controlling SBFS when using the warning system; 80 to 100 gallons outperformed 40 to 50 gallons. At 80 to 100 gallons per acre, however, a sprayer would need to be refilled twice as often as at 40 to 50 gallons per acre, so labor, fuel costs, and overall spray time required would be somewhat greater for the higher volume. However, data presented in this report and elsewhere indicate that the SBFS warning system can cut the number of fungicide sprays for North Central Regions growers by at least two per season, resulting in cost and time savings that are considerably greater than the added costs of refilling a spray tank a few more times. However, the fact that the calendar-timed fungicide spray schedule resulted in an even lower incidence of SBFS than the warning system with higher spray volume suggests that the warning system needs to be further refined in additional field trials, and also that it would be valuable to try applying the warning system with spray volumes exceeding 80 to 100 gallons.

Project Outcomes

Recommendations:

Areas needing additional study

There is a clear need for state and regional marketing research focused on ways to enhance the sales potential of scab-resistant apple cultivars. Wider adoption and greater sales of these high-quality apples would yield benefits for the environmental and economic sustainability of Midwest apple producers. An encouraging sign is increasing openness of supermarket consumers to new apple cultivars (e.g., Jazz, Zestar, Pink Lady) in the past 10 years; receptivity to “new” (or newly promoted) scab-resistant cultivars with excellent eating quality should therefore be higher than in the past. In addition, increased interest in locally grown foods should fit into the local scale of most scab-resistant cultivars.

Additional research is also needed to advance hard cider as a viable option for Upper Midwest growers. Two major needs are for further work on method to produce cider of a consistent quality, and on exploring consumer preferences for the wide range of hard ciders that can be produced with locally or regionally sourced apples. Economic feasibility studies, perhaps using Michigan and New York hard cider industries as case studies, are another critical need to move the industry forward in other Midwest states.

Organic apple production may be the most attractive niche for scab-resistant cultivars. Recent research in northern Europe shows encouraging effectiveness of several organic fungicides against SBFS, but these products need to be evaluated in the Midwest. Codling moth management remains the most formidable obstacle to successful organic apple production in the Midwest. However, combining sprays of granulosis virus with mating disruption has realistic potential to bring codling moth losses down to commercially acceptable levels for organic growers; these strategies need to be further tested in commercial organic orchards.

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.