Final report for ONE20-365
Project Information
The spotted wing Drosophila (SWD), Drosophila suzukii, is a highly invasive insect pest widely distributed throughout the Northeast (and much of the continental USA). Current SWD management recommendations for the Northeastern region lean heavily upon consistently scheduled chemical applications throughout the harvest season. Both the ecological and economic costs of chemical dependence are well documented (e.g. pesticide resistance, non-target organisms, etc.) and are a valid concern. The recent success of a novel food-grade, biodegradable SWD attractant, developed by researchers at Oregon State University, represents a great opportunity to add a new and potentially highly effective alternative to the currently available tactics. Recent preliminary studies from early prototypes deployed on Oregon berry farms suggest these attractant baits can significantly affect SWD behavior and last for up to 21 days. Developers of this innovative tool estimate that these baits exhibit the potential to reduce pesticide dependency “by at least 50% during the cropping season”. Our project assessed the utility and economic viability of this recently developed low-tech tool for the management of spotted wing Drosophila and develop appropriate protocols to best adapt this technology for use on Northeastern berry farms. In concert with our field trials we also developed a robust outreach program in line with our participatory action research (PAR) agenda. Our educational program relied upon research updates, presentations, and individual and remote consultations to best disseminate our results and inform growers of the most appropriate SWD management options.
This project seeks to assess the utility of a recently developed low-tech attractant bait, “Decoy" fruit, for the management of spotted wing Drosophila (SWD) within berry crops on Northeastern farms.
Specifically, our project will look to answer two research questions: 1) How does the application of “Decoy” fruits within berry orchards affect the egg-laying behavior of SWD in berry crops located in New England? And 2) What is the potential of this novel approach for reducing SWD impact on average marketable yields and net revenue for growers with significant investments in berry crops?
This project will provide northeastern growers direct information on the potential of this novel management strategy for reducing SWD damage within berry crops. Furthermore, if our field trials exhibit comparable results to those documented by our collaborators in the Pacific Northwestern growing region of the USA, we will look to develop region specific protocols for the successful use of this novel technology. Ideally this project will add to the currently available IPM tactics for susceptible growers looking to reduce their dependence on chemical controls.
The spotted wing Drosophila (SWD), Drosophila suzukii, is a highly invasive insect pest widely distributed throughout New England (and much of the continental USA). First discovered in the western continental United States in 2008, the SWD rapidly expanded its geographic distribution to include the Pacific Northwest and Southern Canada (Asplen et al. 2015). By 2010 Florida berry growers reported incidences of SWD damage and by the autumn of 2011 select New England growers began to experience significant losses from SWD (Lee et al. 2011, Dean et al. 2013). Since its arrival within the region, SWD has established itself as the primary insect pest of most berries and stone-fruits crops (Farnsworth et al. 2017). While SWD can be found on many plants, its preferred hosts include grapes, cherries, peaches, blueberries, raspberries, strawberries, and other soft-flesh fruits. Unlike the majority Drosophila species, which generally infest over-ripe, rotted or fermenting fruits, SWD adult females exhibit a saw-like ovipositor allowing them to attack fruit during the early stages of ripening(Lee et al. 2011, Asplen et al. 2015). Once infested, larval feeding typically results in extensive fruit rot and/or the loss of fruit integrity. Because SWD is a generalist fruit fly, infestations in New England easily persist throughout much of the late season harvest as populations move across fruit crops that are phenologically staggered(Asplen et al. 2015).
Current SWD management recommendations for the Northeastern region lean heavily upon consistently scheduled chemical applications throughout the harvest season (Beers et al. 2011, Loeb et al. 2013, Van Timmeren and Isaacs 2013). As a result, non-target organisms (e.g. pollinators, natural enemies, etc.), found within the local landscape, are often exposed to both lethal and non-lethal doses of chemical toxins, potentially leading to long-term agroecosystem instability (Belzunces et al. 2012, Stanley and Preetha 2016). Pesticide resistance is also emerging as a major issue for growers utilizing pesticides as a primary management strategy for addressing SWD pressure. This is particularly a concern for organic growers as chemical options are limited and the most effective (and popular) organically certified option for chemical control, spinosad, is already exhibiting reduced efficacy stemming from resistance (Gress and Zalom 2019). A recent study out of central California revealed that fly populations previously exposed to spinosad “exhibited LC50 values 4.3– 7.7 times higher than those from [an] untreated location and 11.6–22.4 times higher than previously reported susceptible baselines” (Gress and Zalom 2019). Though this is the one of the first studies to document the emergence of spinosad resistance in invasive SWD populations, it underscores the potential risk of pesticide resistance emerging in other growing regions.
Cooperators
- - Producer
- - Producer
- - Producer
- (Researcher)
- - Producer
- - Producer
Research
Hypothesis: Application of Decoy bait stations significantly affect the incidence of spotted wing Drosophila in, and the marketability of, various berries grown in the Northeast.
Treatments: Experimental treatments included plots baited with Decoy baits compared to untreated control plots.
Methods: Field trials were conducted at five partner farms: Waterman Orchards in Johnson, VT, in 2021, Last Resort Farm in Monkton, VT, Full Belly Farm in Hinesburg, VT, and Adam’s Berry Farm in Charlotte, VT in 2021, 2022, and 2023, and Sweet Roots Farm in Charlotte, VT, in 2023. We used a Randomized Complete Block Design, whereby randomly assigned plots were assigned to an untreated control dispenser alone (with no Decoy gum) or an experimental treatment of Decoy with dispenser. Treatments were applied by placing the dispensers beneath blueberry plants. Five control plots and five experimental plots were established at each of the partner berry farms. Previous research at Oregon State University (Tait et al. 2018) has shown that the appropriate density of deploying Decoy is 50 dispensers/acre, the equivalent of placing them every 20-30ft within the berry rows. As such, plots were spaced at least 30ft apart. The dispensers were placed prior to the coloring period of fruit, and remained in place through harvest. To ensure the effectiveness of the attractant, ideally the dispensers were kept damp (when possible, farmers hand watered regularly if berries were not drip-irrigated) and were changed every 21 days to ensure they remain attractive throughout data collection.
In 2022, we conducted the trial as described above at Last Resort Farm in Monkton, VT, Full Belly Farm in Hinesburg, VT, and Adam’s Berry Farm in Charlotte, VT. Based on feedback from our collaborators in Oregon, we increased the plot size at Full belly Farm such that a dispenser was placed in two adjacent rows, effectively doubling the size of our plots. Do to the layout of the fields and space limitations at Last Resort Farm and Adam's Berry Farm, we kept the same plot design as the previous year. In 2023, the number of dispensers per plot was increased to two per plot, based on additional feedback from our collaborators in Oregon. Additionally, we added a forth site at Sweet Roots farm in Charlotte, VT.
Data Collection and Analysis: Berries were scouted weekly at each of the field sites throughout the season to confirm the presence of SWD in the research plots. When berries were ripened, we randomly sampled 20 berries from each plot and the number of SWD larvae per berry was assessed using the salt float method. For statistical analysis, the number of SWD larvae per berry was designated as the dependent variable, and differences among treatments was determined via a generalized linear model. Dispenser treatment was considered the single fixed factor. Farm site, trial year and their associated interactions were considered random effects.
Field Season 2021
Key Findings:
- Low SWD pressure at Adam's Berry Farm
- High variability in the amount of SWD pressure on the selected berry farms
- Reduced numbers SWD larvae in berries selected from plants with decoy baits (not statistically significant)
- Small plot sizes and field variability may have contributed to the consistency in our results across plots and farms.
As part of our field research we harvested 5 replicates of 10 berries for each treatment (control & decoy bait) at each farm. Our sampling included four consecutive weeks starting with the onset of berry ripening. The mean number of larvae per sample (10 berries) varied significantly over the course of the sampling period and among farms. The blueberries sampled from the decoy treatment plants did exhibit a reduced number of larvae. Though not statistically significant, the trend was consistent across all farms except Adam's berry farm (see figures below). The high effect variance of the treatments is likely the result of both the limited number of berries sampled and the relatively small plot sizes. To best address these limitations we consulted with Dr. Vaughn Walton of Oregon State (the primary investigator that developed the baits) to decide upon any modification to our methods. Dr. Walton advised that we try to increase our plots sizes to decrease the variability.
2022 Field Season
Key Findings:
- Extremely low SWD pressure across the entire region in 2022
- Lowest SWD pressure again at Adam's Berry Farm
- High variability in the amount of SWD pressure on the selected berry farms
- Reduced numbers SWD larvae in berries selected from plants with decoy baits (not statistically significant)
As part of our field research in 2022, we conducted weekly monitoring on three sites, Adam's Berry Farm, Last Resort Farm, and Full Belly Farm. There was extremely low SWD pressure such that almost no adult flies were detected throughout blueberry season on the three farms. We also sampled berries on two dates, August 8 and August 24, in which we harvested 5 replicates of 10 berries for each treatment (control & decoy bait) at each farm. The mean number of larvae per sample (10 berries) varied significantly over the course of the sampling period and among farms. The blueberries sampled from the decoy treatment plants did exhibit a reduced number of larvae. Though not statistically significant, the trend was consistent across all farms except Adam's berry farm (see figures below). The high effect variance of the treatments is likely the result of both the limited number of berries sampled and the relatively small plot sizes.
2023 Field Season
Key Findings:
- Moderate SWD pressure across the entire region in 2023
- Lowest SWD pressure again at
- High variability in the amount of SWD pressure on the selected berry farms
- No significant difference in number of SWD larvae in berries selected from plants with decoy baits and the control
As part of our field research in 2023, we conducted weekly monitoring on four sites, Adam's Berry Farm, Last Resort Farm, Full Belly Farm, and Sweet Roots Farm. There was moderate SWD pressure such that almost adult flies were detected throughout blueberry season on the three farms, but we did not quantify those data. We sampled berries on two dates, August 2 and August 10, in which we harvested 5 replicates of 20 berries for each treatment (control & decoy bait) at each farm. The first sample period yielded no larvae for all samples except one site that had extremely low numbers of SWD larvae, so no analysis was conducted. For the later sample period, the blueberries sampled from the decoy treatment plants had no significant difference in number of larvae per berry than the blueberrues sampled from the control plants across all sites. There was an interaction between farm and treatment, such that some sites showed higher SWD larvae per berry in the control, whereas others showed higher SWD larvae in the Decoy treated plants (see figures below).
Figure 4. Spotted wing drosophila larvae collected in blueberries on four farms in August 2023
Figure 4. Spotted wing drosophila larvae collected in blueberries, by farm, on four farms in August 2023
We sought to assess the utility of a recently developed low-tech attractant bait, “Decoy" fruit, for the management of spotted wing Drosophila (SWD) within berry crops on Northeastern farms. Specifically, our project looked to answer two research questions: 1) How does the application of “Decoy” fruits within berry orchards affect the egg-laying behavior of SWD in berry crops located in New England? And 2) What is the potential of this novel approach for reducing SWD impact on average marketable yields and net revenue for growers with significant investments in berry crops?
Over the course of three years, we found high variability in the amount of SWD pressure on the selected berry farms, and that SWD pressure varied quite a bit from year to year across the region. We found reduced numbers SWD larvae in berries selected from plants with decoy baits, though the difference was not statistically significant. We believed that small plot sizes and field variability may have contributed to the consistency in our results across plots and farms. As such, we did not find support for the application of “Decoy” within berry orchards affected the egg-laying behavior of SWD in Vermont blueberries, and this novel approach for reducing SWD impact may not be appropriate for our region.
Education & Outreach Activities and Participation Summary
Participation Summary:
Our research team included two UVM educators/PAR researchers and five participating farm partners. As members of the greater UVM Extension community and Plant and Soil Science Dept, the project leaders were well positioned to access all of the available communication channels associated with UVM Extension, including the network of extension professionals who collaborate with our research team (e.g. Cornell Cooperative Extension, UNH Cooperative Extension, UMaine, UMass Extension, Penn State University Extension, etc.) on various other projects.
Knowledge Building: Our outreach curriculum focused upon adaptable information to aid farmers in applying sustainable IPM tactics both new and old for the management of SWD within susceptible fruit crops. Our educational program included weekly updates during key points in the growing season where growers received detailed and practical knowledge on a variety of relevant topics. These topics included the ecology and biology of SWD, currently available control tactics for SWD management, and relevant results stemming from our research trials.
Instructional Methods: Individual and remote consultations directly supported our educational curriculum. Farmer-to-farmer communications were also facilitated through our annual PAR meetings. Weekly updates were disseminated via the Vermont Vegetable & Berry Growers Association ListServ during the growing season, and annual research results from our trials were shared via email and posted on the Institute for Agroecology website (https://www.uvm.edu/instituteforagroecology).
Learning Outcomes
Due to covid restrictions at UVM and our field sites, waning interest in Decoy in the Northeast, and the inconclusive results after three years of data, we refrained from conducting field days. Indirect measurements of grower benefits were assessed via grower communication, and pest consultations. We are confident that our research results and our recommendations for SWD control shared via listserves and grower meetings did positively serve the grower community despite no direct measurement.
Project Outcomes
A key difference between the growing systems in the Pacific Northwest (PNW) where Decoy has shown to be effective, and the northeast where we conducted our trial, is irrigation. Dry conditions in the PNW necessitate daily irrigation and allow for the Decoy to remain moist throughout the deployment period. Our collaborators in the PNW suggested that due to the relatively wetter condition in the Northeast and the lack of daily irrigation, the Decoy may have lost efficacy due to lack of daily watering. In hindsight, Decoy is most likely only going to effective in areas where berry crops are irrigated continuously throughout the growing season, which precludes most berry production in the Northeast.