Final report for GNE17-147
Project Information
The purpose of this research was to investigate UV-blocking (UVO) high tunnel plastic in conjunction with other controls for reducing spotted wing drosophila (SWD) in raspberry. SWD arrived in Pennsylvania in 2012, and has dramatically changed small fruit production, directly impacting crops by laying eggs into ripe and ripening fruit where developing larvae make the fruit unmarketable. SWD has proven difficult to control, even with conventional insecticides, due to limited residual efficacy. Its rapid development and high fecundity allow it to recover quickly from insecticides and indicate a serious risk of resistance development. Organic growers have few effective products and can risk exceeding seasonal application limits. Finally, the increased reliance on insecticides to control SWD has been associated with outbreaks of pest species, like spider mites, typically controlled with natural enemies. SWD control approaches that reduce or eliminate the widespread application of insecticidal sprays are needed.
Based off of preliminary results of sampling SWD populations in high tunnels with different plastic films, we hypothesized that UVO plastics might provide some level of control for SWD. It appeared that the most UV-blocking plastic significantly reduced adult SWD populations compared to plantings without a plastic covering. While this plastic did not have significantly different populations compared to other plastics, there was a trend of lower populations under it, which we suspected might be significantly different with more precise sampling.
Based off of these results, we hypothesized that a push-pull strategy might significantly reduce SWD pressure. In classical push-pull systems, a deterrent (such as an interplanted undesirable species) drives the pest away from the crop, while an adjacent attractant (often a susceptible crop) collects the pest where it will be destroyed. In our system, the UVO plastic would provide the "push," discouraging SWD presence. We chose attracticidal spheres as the "pull." Attracticidal spheres are being developed by the USDA for SWD control; they consist of a red plastic sphere, which is visually attractive to SWD, and a pesticide- and sugar-imbued cap which drips and coats the sphere when moistened, typically with rain and dew. The sugar stimulates feeding, poisoning SWD. The specificity of the sphere means that it has a much lower non-target impact compared to insecticidal sprays, despite containing an active ingredient that is in a common conventional spray.
Besides these push-pull components we chose to examine the effect of daily harvest. We hypothesized that while UVO plastic and attractidicidal spheres might be compatible, they may not fully eliminate infestation. We wanted to know if adding daily harvest could adequately control SWD. We were curious what effects these various control strategies would have on SWD populations and infestation, and we wanted to know if they had additive or interactive effects when combined.
In order to achieve our objectives we performed experiments with high tunnel raspberries that used all combinations of the three variables (UVO plastic, attracticidal spheres, and harvest interval) with two levels of each. We gathered data on total yield, total marketable yield, percent marketable yield, mean fruit weight, infestation rate, and adult presence. While we carried out this experiment, we hosted several tours for the public, including Master Gardener tours and field days. These allowed us to talk about the background of the project, including the impacts and biology of SWD, high tunnel growing systems for raspberries, and our three treatments.
We found that contrary to our preliminary results, UVO plastic did not have a significant effect on SWD infestation. Daily harvest (in comparison with harvesting three times per week) significantly increased the proportion of marketable yield (16-32%) while decreasing infestation (28%). Infestation was measured in marketable fruit, so daily harvest both decreased the amount of fruit culled due to infestation, while decreasing infestation in the marketable fruit (it is typical for marketable fruit on small and organic farms in the Mid Atlantic to have some level of infestation). Attracticidal spheres did not impact the percent marketable yield but did decrease infestation rates (31-50%), which was notable considering that in the tunnel the spheres did not receive the regular rainfall that they rely on for activation in the field.
Treatments had additive effects, showing that combining attracticidal spheres with daily harvest decreased infestation to a greater degree than either treatment by itself. This combined effect was more dramatic under UVO (59-63% reduction), which tended to have higher levels of infestation to begin with. Under UVT plastic, combining treatments reduced infestation by 41-45%, but the infestation rate without treatments was lower.
Only attracticidal spheres impacted populations of adult SWD as measured with apple cider vinegar traps—the presence of spheres reduced SWD in traps about 36%. The results from trapping over the course of the study, as well as monitoring infestation, showed that during the periods of time when we were gathering data, adults and larvae decreased dramatically in all treatments. We suspect that while this may have been due in part to spillover effects of the treatments, it was likely the result of frequent harvest and heightened sanitation during these periods. This emphasized the importance of good sanitation regardless of control approach taken.
Our results have a number of implications for growers. It is important to rule out UVO plastic, which seems to have potential for other pest species, as a control for SWD. UVO plastics are not easily available in the United States at the moment, and not having to “upgrade” is important for cost-saving. Secondly, although harvesting daily did not decrease infestation as much as the use of attracticidal spheres, it did significantly increase marketable yields. In the absence of commercially-available attracticidal spheres, it is also the most effective way to reduce infestation. High tunnels are conducive to daily harvest because they allow harvest all weather.
Although attracticidal spheres are not currently available, they have proven effective in the field, and they should eventually become available. We found that they were effective in tunnels as long as they were occasionally moistened with spray bottles. We also found that they were compatible with daily harvest. A drawback to the spheres is the probability that they won’t be developed for organic use. In preliminary studies, spheres using organic insecticides were ineffective. They currently contain the insecticide Delegate. Even for conventional growers, the season-long reliance on a single chemistry is problematic, and so this technology may need more chemical options before it can really be relied upon.
Objective 1. To evaluate the potential of UVO plastics combined with attracticidal spheres as a push-pull system for decreasing or eliminating SWD infestation in fall-bearing raspberries.
Objective 2. To evaluate decreased harvest interval as an approach to reducing or eliminating SWD infestation within this push-pull system.
Objective 3. To develop non-insecticidal SWD control strategies and through extension programs introduce these strategies to small growers to promote economic and environmental sustainability.
Spotted wing drosophila (Drosophila suzukii Matsumura) (Diptera: Drosophilidae) (SWD) is a recent invasive pest challenging small fruit production in Pennsylvania. SWD is native to southeast Asia and was first observed in cherries in Japan in 1916. It appeared in California in 2008, infesting strawberries and bramble fruits and then spread across North America (Lee et al., 2011). SWD was first observed in Pennsylvania in 2011, with breeding populations established by 2012 (Freda and Braverman, 2013). In Pennsylvania SWD appears in the first and second weeks of July and because of its late emergence in the region it is particularly damaging to late-season small fruits, especially blackberries and primocane-fruiting raspberries (Joshi et al., 2016). The invasion of SWD has likely been facilitated by climate, many alternative hosts, and the lack of natural enemies (Klick et al., 2016; Haye et al., 2016). SWD populations also build up very quickly in favorable conditions, making management challenging. Females lay eggs for their entire lifespan, which may result in the production of more than 400 eggs (Hamby et al., 2016). In some places they may have 13 generations a year (Asplen et al., 2015).
The arrival of SWD has slowed what had been a rapid increase in high tunnel raspberry production in the Northeast (K. Demchak, personal communication). Raspberry is a high-value crop and high tunnel production significantly increases yields and decreases disease pressure (Demchak, 2009; Yao and Rosen, 2011). However, the damage caused by SWD can outweigh these advantages. SWD deposit eggs directly into the fruit, resulting in larvae-infested fruit and the introduction of secondary pathogens (Lee, et al., 2011). SWD must be controlled to avoid crop loss and many growers now spray on a calendar schedule, in some cases requiring five to eight additional sprays per season (Van Timmerman and Isaacs, 2013). In California, seasonal insecticide treatment increased from 1.06 applications per hectare before infestation to 3.7 applications after (Van Steenwyck and Bolda, 2015). For organic production where fewer products are available, efficacy is a challenge and growers risk exceeding maximum seasonal rates (Hanson and Gluck, 2013). Increased reliance on insecticides is harmful to natural enemies and has resulted in outbreaks of secondary pests (Van Steenwyck and Bolda, 2015; Haye et al., 2016; Rogers et al., 2016). Finally, because of the heavy reliance on a narrow range of products, the frequency of their application, and SWD’s short generation time, the risk of insecticide resistance is high (Haye et al., 2016).
IPM techniques remain a challenge. Many different biological controls for SWD, including native North American species, have been investigated, but most only show moderate potential (Haye et al., 2016). Other possible IPM tactics have included mass trapping, semiochemicals, and post-harvest treatment (Lee et al., 2011). None of these were effective on their own, however combinations of several partially effective approaches may improve efficacy. In other specialized cropping systems, push-pull strategies that make the crop unattractive while luring the pest away where it can be destroyed are effective (Cook, et al., 2007). Klick et al. (2016) suggest that alternative host plants, while problematic as refuges, might be valuable for luring SWD away from the crop. Another approach is an attract-and-kill strategy using red spheres with a feeding stimulant and toxicant. The spheres significantly reduced SWD infestation compared to untreated plots and increased the effectiveness of insecticide sprays (Rice et al., 2017). Although push-pull strategies often do not include pesticides, attracticidal spheres are likely to be highly target-specific, luring pests to one place where they are killed, rather than treating entire plantings with insecticides (Cook et al., 2007; Rice et al., 2017a).
High tunnels may make raspberry plantings less attractive to SWD, providing a “push.” SWD numbers were lower in raspberry plantings inside tunnels, compared to those outside. This was attributed to the high tunnel sustaining prolonged periods of temperatures above the development threshold for SWD, and a reduction in relative humidity (Rogers et al., 2016). In another study, where tunnels were covered with Luminance® plastic, similar results were attributed to the extended efficacy of pesticides in the tunnel environment, and possible disruption of visual cues (Leach and Isaacs, 2018). This plastic diffuses radiation and is partially UV-A blocking (K. Demchak, unpublished data). UV-blocking plastics were associated with significantly lower numbers of certain greenhouse pests, including thrips, whiteflies, and aphids, as the elimination of UV light seems to interfere with navigation and behavioral stimuli (Antignus, 2000; Antignus et al., 2001; Doukas and Payne, 2007). Although little is known about SWD vision, research regarding the vision of Drosophila melanogaster (Diptera: Drosophilidae) showed that this species has UV receptors and that UV light is a vital stimulus of positive phototaxis (Schümperli, 1973). SWD foraging may be inhibited by lack of UV light, and thus high tunnels covered with UV-blocking plastic may help provide some degree of control.
In addition to these approaches, removing excessive foliage and infested fruit can help control SWD infestation (Hamby et al., 2016; Haye et al., 2016). Shortening harvest intervals to every two days significantly reduced infestation in Swiss raspberry plantings compared to longer intervals (Haye et al., 2016). Recent work in high tunnel raspberries found that shortening the harvest interval from 3 days to daily or every other day significantly reduced infestation. However, shortening the harvest interval did not eliminate infestation, and it was recommended that the shortened harvest interval be combined with pesticide application for greatest effect (Leach et al., 2017). While shortening the harvest interval is not a stand-alone solution to SWD infestation, it does provide another degree of control. The technique is especially suited to tunnel production where the ability to harvest regularly despite unfavorable weather can aid sanitation efforts.
It is likely that combining several non-spray control approaches could have additive effects and reduce SWD infestation beyond what a single approach can provide. It is not known if the approaches of using UV-blocking high tunnel films, attracticidal spheres, and shortened harvest interval are compatible or additive. It is also important to establish the effectiveness of spheres in high tunnels, as their efficacy in the field relies on wetting from rain and dew in the environment (Rice, et al., 2017). It is also not clear whether UV-blocking plastics impact SWD the way they impact other insects. Finally, whether any of these tactics might have interactive effects is unknown.
The purpose of this study was to evaluate the efficacy of these three approaches alone and combined for reducing SWD infestation in raspberries grown in high tunnels
References.
Antignus, Y. 2000. Manipulation of wavelength-dependent behavior of insects: an IPM tool to impede insects and restrict epidemics of insect-borne viruses. Virus Res. 71:213-220.
Antignus, Y., D. Nestel, S. Cohen, and M. Lapidot. 2001. Ultraviolet-deficient greenhouse environment affects Whitefly attraction and flight behavior. Environ. Ent. 30:394-399.
Asplen, M.K., G. Anfora, A. Biondi, D. Choi, D. Chu, K.M. Daane, P. Gilbert, A.P. Gutierrez, K.A. Hoelmer, W.D. Hutchinson, R. Isaacs, Z. Jiang, Z. Kárpáti, M.T. Kimura, M. Pascual, C.R. Phillips, C. Plantamp, L. Ponti, G. Vétek, H. Vogt, V.M. Walton, Y. Yu, L. Zappala, and N. Desneux. 2015. Invasion biology of spotted wing Drosophila (Drosophila suzukii): a global perspective. J Pest Sci. 88:469-494.
Cook, S.M., Z.R. Kahn, and J.A. Pickett. 2007. The use of push-pull strategies in integrated pest management. Ann. Rev. Entomol. 52:375-400.
Demchak, K. 2009. Small fruit production in high tunnels. HortTechnology 19:44-49.
Doukas, D. and C.C. Payne. 2007. The use of ultraviolet-blocking films in insect pest management in the UK; effects on naturally occurring arthropod pest and natural enemy populations in a protected cucumber crop. Ann. Appl. Biol. 151: 221-231.
Freda, P.J. and J.M. Braverman. 2013 Drosophila suzukii, or Spotted Wing Drosophila, recorded in southwestern Pennsylvania, U.S.A. Entom. News. 123(1): 71-75.
Hamby, K., D.E. Bellamy, J.C. Chiu, J.C. Lee, V.M. Walton, N.G. Wilman, R.M. York, and A. Biondi. 2016. Biotic and abiotic factors impacting development, behavior, phenology, and reproductive biology of Drosophila suzukii. J. Pest. Sci. 89:605-619.
Hanson, E.J. and B.I. Gluck. 2013. High tunnels for organic raspberry production in the Midwestern US. Proc. IInd Intl. Organic Fruit Symp. Acta Hort. 1001:73-77.
Haye, T., P. Girod, A.G.S. Cuthbertson, X.G. Wang, K.M. Daane, K.A. Hoelmer, C. Baroffio, J.P. Zhang, and N. Desneux. 2016. Current SWD IPM practices and their practical implementation in fruit crops across different regions around the world. J. Pest. Sci. 89:643-651.
Joshi, N.K., B. Butler, K. Demchak, and D. Biddinger. 2016. Seasonal occurrence of spotted wing drosophila in various small fruits and berries in Pennsylvania and Maryland. J. Appl. Entomol. 141:156-160.
Klick, J., W.Q. Yang, V.M. Walton, D.T. Dalton, J.R. Hagler, A.J. Dreves, J.C. Lee, and D.J. Bruck. 2016. Distribution and activity of Drosophila suzukii in cultivated raspberry and surrounding vegetation. J. Appl. Entomol. 140:37-46.
Leach, H. and R. Isaacs. 2018. Seasonal occurrence of key arthropod pests and beneficial insects in Michigan high tunnels and field grown raspberries. Envir. Entomol. 47(3): 567-574.
Leach, H., J. Moses, E. Hanson, P. Fanning, and R. Isaacs. 2017. Rapid harvest schedules and fruit removal as non-chemical approaches for managing Spotted Wing Drosophila. J. Pest. Sci. 91:219-226.
Lee, J.C., D.J. Bruck, A.J. Dreves, C. Loriatti, H. Vogt, and P. Baulfield. 2011. In Focus: Spotted Wing Drosophila across perspectives. Pest. Manag. Sci. 67:1349-1351.
Rice, K.B., B.D. Short, and T.C. Leskey. 2017. Development of an attract-and-kill strategy for Drosophila suzukii (Diptera: Drosophilidae): evaluation of attracticidal spheres under laboratory and field conditions. J. Econ. Entomol. 110(2):535-542.
Rogers, M.A., E.C. Burkness, and W.D. Hutchinson. 2016. Evaluation of high tunnels for management of Drosophila suzukii in fall-bearing red raspberries: potential for reducing insecticide use. J Pest Sci. 89:815-821.
Schümperli, R.A. 1973. Evidence for color vision in Drosophila melanogaster through spontaneous phototactic behavior. J. Comp. Physiol. 86:77-94.
Van Steenwyck, R.A. and M.P. Bolda. 2015. Spotted wing drosophila: devastating effects on cherry and berry pest management. Proc. Int. Symp. on Innovative Plant Protection in Horticulture. Acta Hort. 1105.2.
Van Timmeren, S. and R. Issacs. 2013. Control of spotted wing drosophila, Drosophila suzukii, by specific insecticides and by conventional and organic crop protection programs. Crop Protect. 54:126-133.
Yao, S. and C. J. Rosen. 2011. Primocane fruiting raspberry production in high tunnels in a cold region of the upper midwestern United States. HortTechnology 21(4): 429-434.
Research
Design: This experiment was conducted at the Russell E. Larson Agricultural Research Center in Rock Springs, PA (latitude: 40-57’ 19” N, longitude 078-44’ 14” W). In 2018, six research-sized high tunnels (5.18 m by 10.67 m) were used for this experiment. Three tunnels were covered with either UV-blocking or UV-transmitting plastic. They had fixed endwalls throughout this study which were covered with the same plastic as the tunnel tops and sides, with a door in the south end. The tunnels were manually vented with roll-up sides.
Each tunnel was divided into two halves by vertically suspending 0.35 mm x 0.35 mm ProtekNet™ insect netting (Nolt’s Produce Supplies, Leola, PA) from ceiling to floor and treatments of attracticidal spheres or no spheres were randomly assigned to each half. Each tunnel half contained two parallel plots of 8 primocane-fruiting ‘Josephine’ plants (Nourse Farms, South Deerfield, MA) which had been planted in 11.36 L plastic nursery bags (Hydro-Gardens Inc., Colorado Springs, Co) in June 2016, and repotted into 18.93 L bags in 2017. Additional plants were planted into 18.93 L bags in 2017 to serve as guard plants and placed at the ends of each plot. Plants were grown in a 2:1 peat:perlite medium and fertigated throughout the season with 20N-3.1P-16.6K general purpose fertilizer for alkaline water (Plant Marvel, Chicago Heights, IL), supplying nitrogen at 100 mg·L-1. Plants were spaced on 0.3 m centers within rows and rows were spaced 2.6 m apart. Plants were pruned and trellised to regulate canopy density and to facilitate harvest.
One row of plants in each tunnel half was harvested daily and the other half was harvested three time per week. The experimental design was a split-split-plot, where plastic tunnel cover was the whole plot factor, attracticidal spheres was the split-plot factor, and harvest interval was the split-split-plot factor. Each combination was replicated three times.
Plastics. In 2015, percent transmittance of radiation for the plastics was determined with a StellarNet model EPP2000 (StellarNet, Inc., Tampa, FL) spectroradiometer calibrated to National Institute of Standards and Technology (NIST) sources at the USDA-ARS Appalachian Fruit Research lab in Kearneysville, WV. These measurements were used to validate the limited descriptions of transmittances from the plastic manufacturers, and to provide information where none was available. In 2018, spectral distributions within the tunnels were measured on cloudless days with an Apogee Model PS-300 spectroradiometer equipped with a cosine-corrected detector (Apogee Instruments, Logan UT). The sensor was placed in the center of the tunnel, varying from the center by a maximum of 20 cm to avoid shadows from the tunnel structure, and at a height of 1 m above the ground. Light intensity (µmol/m2/sec) was measured within each tunnel, as well as between tunnels for comparison. The sensor was contained in a leveling fixture and thus was held level for each reading. The transmittance at each wavelength within the UV-B (280-315 nm), UV-A (315-400 nm), and visible (400-700) ranges were summed and compared to outside light levels and were expressed as percent transmittance for both plastics within each of these ranges. The plastics used in this experiment, along with abbreviations used to refer to them, were two custom-manufactured experimental plastics, one UV-transparent “UVT” and one UV-blocking (or opaque) “UVO” (BPI-Visqueen, Stevenston, U.K.; currently available through Lightworks Poly, Lancashire, U.K.).
Attracticidal spheres. Spheres consisted of two parts: the flat-topped red plastic bases (Great Lakes IPM, Vestaburg, MI), and sphere caps that were manufactured for this experiment at the USDA-ARS Appalachian Fruit Research lab in Kearneysville, WV, following the procedure outlined by Rice et al. (2017). Sphere caps contained the pesticide Delegate (Dow AgroSciences, Indianapolis, IN) at 1% by weight. One sphere was deployed for every two plants, for a total of four spheres per plot, or eight spheres in each tunnel half with the sphere treatment. Two spheres were hung from trellis wires on each side of the row. From 21 to 31 Aug. spheres were hung at about 0.85 m and from 17 to 28 Sept. at about 1.33 m above ground level. Spheres were misted with a spray bottle (L. G. Sourcing, N. Wilkesboro, NC) on low-humidity days when they appeared visibly dry. Once between Aug. and Sept., spheres were removed, caps discarded, the plastic bases cleaned, and a new set of caps applied.
Harvest interval. A shortened interval of daily harvest was based on previous literature (Haye et al., 2016; Leach et al., 2017). Plots were harvested daily or three times per week (Mon., Weds., Fri.), the research farm’s standard harvest interval. All fully-colored fruit that easily detached from the receptacle were harvested by two assistants trained in this harvesting procedure. Fruit was harvested at these intervals for two 12-day periods, 21-31 Aug. (“Experiment 1”) and 17-28 Sept. (“Experiment 2”).
Yield data. Harvested fruit was sorted into marketable and unmarketable categories. Marketable fruit was firm and unblemished, while any fruit that had damage, was deformed, crumbly, or was soft (indicating SWD infestation) was considered unmarketable. For each date, the weight (g) of marketable and unmarketable fruit in each treatment, and mean fruit weight estimated from a 50-fruit subsample, were recorded for each plot.
Monitoring fruit infestation. The saline-float method outlined by Van Timmerman et al. (2017) was used to monitor fruit infestation. Samples of up to 50 marketable fruit were placed in resealable 3.8 L freezer bags. The fruit were gently crushed and 250 to 500 ml of salt solution was added to each sample (312.6 g non-iodized salt for 3.8 L water). The samples rested one hour before filtering through 5 mm hardware cloth placed in a plastic canning funnel (Nopro, Inc, Everett, WA) to catch fruit, and then through a reusable metal basket coffee filter (Medelco Inc, Bridgeport, CT) to catch SWD larvae and eggs. The coffee filter was then examined under a dissecting microscope, and the numbers of eggs, first-, second-, and third-instar larvae were counted. First- and second-instar larvae were not differentiated. Infestation rates were calculated by dividing the total number of larvae by the number of fruit in the sample. Eggs are not reliably separated from the fruit with this method (Van Timmerman et al., 2017), so egg data were not analyzed.
Adult trap data. Adult SWD were monitored with apple cider vinegar traps. Traps made with plastic deli containers (0.95 l) (Plastic Packaging Corporation, Springfield, MA) with 3.6 mm holes drilled in the sides to allow SWD to enter and to exclude larger insects were suspended from a center trellis line inside the raspberry foliage to maximize humidity and darkness. Traps were filled with approximately 250 ml of an apple cider vinegar and unscented dish soap solution. Every seven days trap contents were filtered through a mesh half-sphere and stored in vials for later identification with a dissecting scope. Numbers of male and female SWD and other fruit flies and insects were counted and recorded. SWD were first captured on 19 July.
Statistical analyses. Data were analyzed with SAS 9.4 (SAS Institute, Carey, NC) and visualized with Tableau Desktop 2018.2 (Tableau Software Inc, Seattle, WA). Trap data were analyzed as a split-split-plot design by analysis of variance with SAS’s PROC GLIMMIX. Plastic was the whole-plot, sphere treatment was the split-plot, and harvest interval the split-split-plot. The treatment structure was a 2 x 2 x 2 x 6 factorial (2 levels of each treatment and 6 collection dates).
Data for yield and SWD infestation from the daily harvest plots were combined to obtain the same number of observations for both harvest-interval treatments. The first date of each of the two-week data collection periods was not included in analysis, because there would have not yet been harvest interval treatment effects. Data from each two-week harvest period were analyzed as separate experiments. These data were tested for equal variances with all combinations of harvest date, sphere treatment, harvest interval, and plastic treatment (4-way factorial) by requesting absolute residuals with SAS’s PROC GLM. Levene’s test was used to evaluate homogeneity of variances at the 1% level of significance. When variances were not equal, analysis of variance (ANOVA) was performed with PROC MIXED using a heterogeneous variance model. When interactions were not significant, the F-test from the ANOVA was used to test equality of main effect means. As there were only two levels of each treatment, further tests were not required to determine differences between treatments.
References.
Haye, T., P. Girod, A. G. S. Cuthbertson, X. G. Wang, K. M. Daane, K. A. Hoelmer, C. Baroffio, J. P. Zhang, and N. Desneux. 2016. Current SWD IPM practices and their practical implementation in fruit crops across different regions around the world. J. Pest. Sci. 89:643-651.
Leach, H., J. Moses, E. Hanson, P. Fanning, and R. Isaacs. 2017. Rapid harvest schedules and fruit removal as non-chemical approaches for managing Spotted Wing Drosophila. J. Pest. Sci. 91:219-226.
Rice, K.B., B.D. Short, and T.C. Leskey. 2017. Development of an attract-and-kill strategy for Drosophila suzukii (Diptera: Drosophilidae): evaluation of attracticidal spheres under laboratory and field conditions. J. Econ. Entomol. 110(2):535-542.
Van Timmeren, S., L.M. Diepenbrock, M.A. Bertone, H.J. Burrack, and R. Isaacs. 2017. A filter method for improved monitoring of Drosophila suzukii (Diptera: Drosophilidae) larvae in fruit. J. Integ. Pest Manag. 8(1):23; 1-7.
Treatment effects on yield. Of the three treatments, only harvest interval significantly affected marketable yield, the percent of marketable fruit, and fruit weight (Tables 1 and 2). In Experiment 1 the mean proportion of marketable fruit for plots harvested three times a week was 49% versus 72% for plots harvested daily (Table 1). In Experiment 2 the difference between the harvest interval treatments was smaller, but still significant (55% vs. 66%) (Table 2). This 17-32% yield increase may be economically beneficial for growers, for whom the presence of SWD has dramatically decreased marketable yields (Bolda et al., 2010). The majority of unmarketable fruit showed signs of infestation, so the significant increase in marketable fruit suggests that the daily harvest decreased infestation. This was important for Objectives 2 of the project, where we sought to explore shortened harvest interval for decreasing SWD losses. It also suggests shortened harvest interval as a solution to Objective 3, seeking non-chemical approaches to SWD control.
Total yields (marketable and unmarketable fruit for each plot) were 28% higher for Experiment 1 than for the second experiment, possibly because plants were pruned at the conclusion of Experiment 1, removing some of the fruiting canes. Low temperatures in Sept. also likely delayed fruit ripening in Experiment 2. No treatments or interactions affected total yield (data not shown). The lack of difference between harvest intervals contradicts a previous study where daily harvested plots had lower yields compared to longer harvest intervals (Leach et al., 2017). The authors attributed higher yields to larger fruit size due to longer ripening times in less-frequently harvested plots and our contradictory results may have been due to different ripening patterns between the cultivars tested. We found it encouraging that daily harvest did not decrease our total yields, which further recommends it as an approach for SWD control.
Total marketable yield in Experiment 1 was significantly affected by interval (Table 1). In Experiment 2 harvest interval was again significant, as were the interactions of sphere x interval and plastic x sphere x interval (Table 2). In both experiments marketable yield was always higher for plots harvested daily than for those harvested at three-day intervals (33% higher in Experiment 1, and 43% higher in Experiment 2). This was likely because frequent harvest increased the amount of fruit without signs of infestation.
Mean fruit weight was affected by harvest interval in Experiment 1 but not Experiment 2 (Tables 1 and 2). In Experiment 1, plots harvested more frequently consistently had lower mean fruit weight, but the difference was only 0.2 g (3.5 g vs. 3.3 g). Weight of red raspberry fruit may increase 25% after they reach full-color, which may explain why fruit allowed an additional day of ripening would weigh more (Ramsay, 1983). This difference may be significant for growers who are filling containers for wholesale but may not be important for a smaller grower or a pick-your-own operation. In Experiment 1 interactions were not significant, but in Experiment 2 plastic x harvest interval was significant, though differences in fruit weight were small (Table 2).
Treatment effects on infestation. In the first experiment, the number of larvae per marketable fruit was significantly affected by sphere treatment and harvest interval (Table 3). In Experiment 2, sphere, and harvest interval were significant at p=0.06 (Table 3). The presence of spheres reduced the mean number of larvae per marketable fruit 31% in Experiment 1 and 48% in Experiment 2. Results for the sphere treatment agree with previous research in field-grown raspberries, where attracticidal sphere treatments significantly reduced the number of larvae per fruit compared with non-treated controls. In previous research in field-grown raspberries, fruit from non-treated plots had more than 4 larvae per fruit, whereas fruit from the plots with spheres had fewer than 2 per larvae per fruit (Rice et al., 2017). Although infestation levels were lower in our trial (0.65 and 0.45 in the first experiment and 0.5 and 0.26 in the second), possibly due to more frequent harvest or the effects of high tunnel temperatures, the treatment effects were similar.
In previous experiments spheres were used in field settings and relied on rainfall and dew to moisten the sugar and toxicant. Adult SWD feed on the sphere’s liquid coating and are poisoned (Rice et al., 2017). We hypothesized that the dry environment in tunnels might reduce the efficacy of the spheres. To combat this we misted the spheres on sunny, dry days with water. On days with rain or high humidity the spheres appeared wet despite not being exposed to rain. Our results suggest that misting the spheres by hand on dry days was sufficient to keep them activated and that this technology is compatible with high tunnel production. We also found significant effects with one sphere for every two plants, despite the large size of the plants. We suspect that increasing the density of spheres in high tunnels with large plants could further decrease infestation, although this assumption needs to be verified by further research.
Non-target arthropods were impacted to some degree by the spheres. Lady beetles (Family: Coccinelidae) were observed on some spheres, as were occasional Lepidopterans. Although not quantified, adverse effects to non-target organisms from the spheres was likely less than would be expected from pesticide applications. Even when used in attract-and-kill technology, insecticides are applied at far lower rates than conventional treatments (El-Sayed, et al., 2009) and they appear to have minimal impacts on pollinators (T. Leskey, personal communication). A barrier to grower use is that the spheres are currently under development and obtaining registration for this technology may be slow. Spinetoram (marketed as Delegate), the active ingredient for the spheres, is widely used for SWD control. Although considered a low-risk insecticide with reduced impact on non-target organisms, Delegate is not approved for organic use (Piñero and Byers, 2013). Rice et al. (2017) tested different toxicants for attracticidal spheres and all the organic pesticides tested had low efficacy and residual activity against SWD. Therefore, development of effective spheres for organic growers is unlikely. Research would be beneficial to develop a variety of chemistries for the spheres and possibly to develop a system of temporal or spatial refuges to reduce the risk of resistance.
Although UVO plastic was not significant, we were able to assess the effectiveness of attracticidal spheres under high tunnels conditions. This addresses Objective 1, where we learned a great deal about the use of attracticidal spheres in conjunction with tunnel culture. While the attracticidal spheres use insecticides, they are still relevant to Objective 3, as they are a tactic that would decrease overall insecticide use.
In Experiment 1 the mean larvae per fruit was 0.64 for daily harvest and 0.46 for three-day harvest (a 28% reduction). In Experiment 2 the number of larvae per fruit was 0.43 and 0.30 (a 30% reduction). Our finding that harvest interval affects the number of larvae per fruit is supported by previous research where reduced infestation was associated with more frequent harvest (Haye et al., 2016; Leach et al., 2017). This reduction in infestation combined with increases in yield further shows daily harvest to be a valuable practice in conjunction with tunnels and attracticidal spheres for reducing SWD infestation without insecticidal spray applications, addressing Objectives 2 and 3.
Impact of date on treatment. We found that infestation was significantly affected by harvest date in both experiments (Table 3). For both experiments and all treatments, infestation decreased over time within each experiment. This was supported by the trends in adult trap capture from the vinegar traps where date was also significant (p=0.0076). Pooled over all the treatments, traps show SWD numbers peaking at the beginning of each experimental period then falling over the course of the experiments (Fig. 1). While daily harvest and sphere treatments had lower infestation rates than 3 times a week harvest and no spheres, all the treatments followed similar patterns as they declined over time. This suggests that the treatment effects might have spilled over: spheres in one half of the tunnel may have affected SWD populations on the side without spheres, as the flies can easily move short distances. This suggests that growers using these treatments over the course of a season might have even lower mean infestation than we found. Sanitation was likely important as well. At a given time, the majority of SWD are in the larval or pupal stage, not adult (Wiman et al., 2014), so frequently picking and removing infested fruit targets these life stages and can have a significant effect on adult populations.
When adult trap captures were analyzed, only sphere treatment significantly affected the number of SWD captured in vinegar traps, and there were no significant interactions (Table 4). Spheres reduced populations 36%, which was similar to the results for infestation.
Treatment combination. The sphere x interval interaction was significant in Experiment 2 (Table 3). In the absence of spheres, daily harvest decreased infestation 48%, but when spheres were used there was a 2% increase associated with daily harvest. However, the infestation rate with spheres was lower than daily harvest without spheres whether or not fruit was harvested daily (0.25 versus 0.48). While this suggests that daily harvest does not provide any additional decrease in infestation when combined with the other technologies that reduce infestation, in Experiment 1 there were no significant interactions and the treatments appeared to be additive. It is not clear from the two experimental periods in our study whether harvest interval and spheres will always interact. However, even if harvesting daily does not significantly decrease infestation, the increase in marketable fruit still makes it a worthwhile practice.
Our data show that using certain treatments in combination can have additive effects on infestation. Under UVO plastic, combining daily harvest and spheres lowered infestation from 59-63% compared to three times per week harvest and no spheres. Many growers use TIV, the commercially-available plastic that has very similar transmittance to UVT (Cramer et al., 2019, submitted), so the results from UVT are particularly relevant. Under UVT plastic, the combination of daily harvest and spheres reduced infestation 41-45% compared to three times per week harvest and no spheres. Our results suggest that it’s likely these reductions would be even more pronounced with sustained use of the treatments.
Our results do not provide incentive for high tunnel raspberry growers to change their plastic covering but do suggest that shortened harvest interval and attracticidal spheres can be combined for increased control. They provide the useful information that UV-blocking plastics should probably not continue to be pursued as a control strategy as there was no evidence that UVO plastic deterred adults or decreased infestation. When spheres become available they will be an effective technology in high tunnels and can be combined with practices such as daily harvest and sanitation to reduce the need for insecticidal sprays.
Tables and Figures.
Table 1. Exp. 1: Effects of UV-blocking plastic, attracticidal spheres, and shortened harvest interval on yield parameters of ‘Josephine’ raspberry grown in high tunnels at Rock Springs, PA in August, 2018.
Main effects least squared means and standard errors
Plastic Marketable Yield(g) %Marketable Mean Fruit Weight(g)
UVO 163.5±10.0 60±1.1% 3.4±0.08
UVT 180.3±10.0 62±1.1% 3.4±0.08
Spheres
Yes 165.0±10.4 60±1.1% 3.4±0.09
No 178.7±10.4 61±1.1% 3.3±0.09
Interval
Daily 206.0±9.9 72±1.1% 3.3±0.08
3xs 137.7±9.9 49±1.1% 3.5±0.08
Interaction least squared means
Plast. Int. Sphere Marketable Yield(g) %Marketable Mean Fruit Weight (g)
UVO 3xs No 143.3±18.5 51±2.1% 3.5±0.12
UVO Daily No 181.4±18.5 71±2.2% 3.3±0.12
UVO 3xs Yes 128.6±18.5 45±2.1% 3.4±0.12
UVO Daily Yes 200.6±18.5 72±2.1% 3.2±0.12
UVT 3xs No 149.2±18.5 49±2.1% 3.6±0.12
UVT Daily No 240.9±18.5 73±2.1% 3.2±0.12
UVT 3xs Yes 129.0±18.5 51±2.1% 3.4±0.12
UVT Daily Yes 201.1±18.5 73±2.1% 3.3±0.12
ANOVA results
Effect Marketable Yield (g) %Marketable Mean Fruit Weight (g)
F-value DF P F-value DF P F-value DF P
Plastic 1.64 1, 15.7 0.2168 1.44 1, 4.2 0.2939 0.01 1, 5.02 0.9406
Sphere 0.93 1, 18.6 0.3468 0.68 1, 7.97 0.4325 0.82 1, 6.59 0.397
Interval 28.82 1, 15.5 <0.0001 246.03 1, 7.47 <0.0001 8.36 1, 5.05 0.0337
Plastic*sphere 1.73 1, 13.4 0.2106 2.12 1, 7.97 0.1838 0.07 1, 4.72 0.8032
Plastic*interval 1.14 1, 14.4 0.3025 0.03 1, 7.47 0.8704 1.12 1, 4.02 0.3499
Sphere*interval 0.07 1, 14.4 0.7924 0.59 1, 7.97 0.4654 0.70 1, 4.33 0.4477
Plastic*sphere*interval 1.26 1, 13.4 0.2815 2.98 1, 7.97 0.1227 0.71 1, 4.02 0.4452
Date 11.39 4, 9.07 <0.0001 12.79 4, 9.63 0.0007 12.95 4, 8 0.0014
Table 2. Exp. 2: Effects of UV-blocking plastic, attracticidal spheres, and shortened harvest interval on yield parameters of ‘Josephine’ raspberry grown in high tunnels at Rock Springs, PA in September, 2018.
Main effects least squared means and standard errors
Plastic Marketable Yield(g) %Marketable Mean Fruit Weight(g)
UVO 109.1±10.8 58±2% 3.3±0.07
UVT 116.4±10.8 62±2% 3.3±0.07
Spheres
Yes 118.0±10.3 61±2% 3.3±0.07
No 107.5±10.3 60±2% 3.3±0.07
Interval
Daily 144.0±9.3 66±2% 3.3±0.06
3xs 81.5±9.3 55±2% 3.3±0.06
Interaction least squared means
Plast. Int. Spheres Marketable Yield (g) %Marketable Mean Fruit Weight (g)
UVO 3xs No 76.60±16.0 53±4% 3.3±0.11
UVO Daily No 151.3±16.0 63±4% 3.3±0.11
UVO 3xs Yes 62.30±16.0 50±4% 3.1±0.11
UVO Daily Yes 144.4±16.2 65±4% 3.3±0.11
UVT 3xs No 92.70±16.0 55±4% 3.3±0.11
UVT Daily No 109.2±16.0 67±4% 3.2±0.11
UVT 3xs Yes 94.50±16.0 60±4% 3.5±0.11
UVT Daily Yes 168.9±16.0 67±4% 3.3±0.11
ANOVA results
Effect Marketable Yield (g) %Marketable Mean Fruit Weight (g)
F-value DF P F-value DF P F-value DF P
Plastic 0.24 1, 9.61 0.6346 2.51 1, 15.7 0.1331 0.56 1, 4.07 0.4966
Sphere 0.65 1, 7.44 0.4459 0.2 1, 5.7 0.6597 0.36 1, 3.97 0.5833
Interval 40.09 1, 5.72 0.0009 18.14 1, 5.7 0.0006 0.16 1, 8.33 0.7024
Plastic*sphere 2.68 1, 6.7 0.1477 0.31 1, 15.7 0.5911 1.13 1, 3.86 0.3495
Plastic*interval 3.7 1, 5.37 0.1085 0.25 1, 15.7 0.624 9.66 1, 6.9 0.0174
Sphere*interval 7.05 1, 4.04 0.0561 0.01 1, 15.7 0.9388 0.00 1, 8.33 0.9931
Plastic*sphere*interval 7.11 1, 32.1 0.0119 0.90 1, 15.7 0.3577 3.46 1, 6.9 0.1059
Date 24.23 4, 8.63 0.0001 10.14 4, 63 <.0001 3.04 4, 15.4 0.0497
Table 3. Effects of UV-blocking plastic, attracticidal spheres, and shortened harvest interval on SWD infestation of marketable 'Josephine' red raspberry fruit in Experiments 1 & 2.
Main effect least squared means and standard error
Plastic Exp. 1 Larvae/fruit Exp. 2 Larvae/fruit
UVO 0.53±0.11 0.42±0.06
UVT 0.57±0.11 0.31±0.06
Spheres
Yes 0.45±0.10 0.26±0.06
No 0.65±0.10 0.50±0.06
Interval
Daily 0.46±0.10 0.30±0.05
3xs 0.64±0.10 0.43±0.05
Interaction least squared means
Plastic Interval Spheres
UVO 3xs No 0.82±0.13 0.75±0.09
UVO Daily No 0.51±0.13 0.31±0.09
UVO 3xs Yes 0.44±0.13 0.34±0.09
UVO Daily Yes 0.34±0.13 0.28±0.09
UVT 3xs No 0.75±0.13 0.51±0.08
UVT Daily No 0.53±0.13 0.34±0.08
UVT 3xs Yes 0.56±0.13 0.13±0.08
UVT Daily Yes 0.44±0.13 0.28±0.08
ANOVA results
Effect F-value DF P-value F-value DF P-value
Plastic 0.16 1, 2 0.7278 2.05 1, 8.37 0.1888
Sphere 7.41 1, 4.59 0.0456 10.18 1, 2.86 0.0531
Interval 10.39 1, 10 0.0091 4.14 1, 20.3 0.0551
Plastic*sphere 0.95 1, 3.47 0.3931 0.00 1, 2.95 0.9711
Plastic*interval 0.22 1, 36.1 0.6408 3.63 1, 20.3 0.0711
Sphere*interval 2.43 1, 18.2 0.136 15.06 1, 34.3 0.0004
Plastic*sphere*interval 0.45 1, 36.1 0.5068 0.06 1, 34.3 0.8036
Date 20.85 4, 8 0.0003 26.46 4, 16.8 <.0001
Table 4. Least squared mean weekly trap captures in of adult SWD in 2018 under plastic film, sphere, and harvest interval treatments in 'Josephine' red raspberries grown in Rock Springs, PA.
Treatment Mean capture
Plastic
UVO 99.7±15.32
UVT 118.4±15.32
Sphere
Yes 83.0±14.3
No 135.1±14.3
Interval
Daily 96.5±14.3
3xs 121.7±14.3
ANOVA results
F-value DF p-value
Plastic 1.23 1, 2 0.3824
Sphere 16.62 1, 12 0.0015
Interval 3.88 1, 12 0.0725
Plastic*sphere 0.01 1, 12 0.9275
Plastic*interval 0.69 1, 12 0.4226
Sphere*interval 2.45 1, 12 0.1437
Plastic*sphere*interval 0.06 1, 12 0.8071
Date 10.92 3, 6 0.0076
Figure 1. Mean number of SWD per trap per week in 'Josephine' red raspberry grown in high tunnels over time during two data collection periods in 2018 at Rock Springs, PA.
References
Bolda, M., R.E. Goodhue, F.G. Zalom. 2010. Spotted wing drosophila: otential economic impact of a newly established pest. Agricultural and Resource Economics Update, niversity of California, Gianini Foundation, 13:5-8.
El-Sayed, A.M., D.M. Suckling, J.A. Byers, E.B. Jang, C.H. Wearing. 2009. Potential of “lure and kill” in long-term pest management and eradication of invasive species. J. Econ. Entomol. 102(3): 815-835.
Haye, T., P. Girod, A.G.S. Cuthbertson, X.G. Wang, K.M. Daane, K.A. Hoelmer, C. Baroffio, J.P. Zhang, and N. Desneux. 2016. Current SWD IPM practices and their practical implementation in fruit crops across different regions around the world. J. Pest. Sci. 89:643-651.
Leach, H. and R. Isaacs. 2018. Seasonal occurrence of key arthropod pests and beneficial insects in Michigan high tunnels and field grown raspberries. Envir. Entomol. 47(3): 567-574.
Ramsay, A.M. 1983. Mechanical harvesting of raspberries-- a review with particular reference to engineering development in Scotland. J. agric. Engng. Res. 28: 183-206.
Rice, K.B., B.D. Short, and T.C. Leskey. 2017. Development of an attract-and-kill strategy for Drosophila suzukii (Diptera: Drosophilidae): evaluation of attracticidal spheres under laboratory and field conditions. J. Econ. Entomol. 110(2):535-542.
Wiman, N.G., V.M. Walton, D.T. Dalton, G. Anfora, H.J. Burrack, J.C. Chiu, K.M. Daane, A. Grassi, B. Miller, S. Tochen, X. Wang, C. Loriatti. 2014. Integrating Temperature-Dependent Life Table Data into a Matrix Projection Model for Drosophila suzukii Population Estimation. PLoS ONE 9(9): e106909. doi:10.1371/journal.pone.0106909
Our research suggests several key conclusions. The first is that while it's been found in previous research that UVO plastic discourages the presence of other insect orders, it does not discourage SWD presence. Using a UV-blocking plastic provides no level of reduction of either adult flies or infestation in the fruit.
While UVO plastic was ineffective, we did find that the treatments we hoped to combine with it were effective on their own and in combination in high tunnels. We found that daily harvest both increased yields significantly and decreased infestation. We also found that using attracticidal spheres in tunnels significantly decreased infestation.
We found that daily harvest and attracticidal spheres were compatible. In our first experiment we found that they had additive effects when combined, further lowering SWD infestation. Although in Experiment 2 they did not appear to be additive, the increase in yield from daily harvest still recommends using both treatments.
Finally, we found that these treatments and rigorous sanitation seems to decrease infestation dramatically over time. This suggests that growers using these practices for an extended period of time may see significantly lowered infestation while avoiding spraying insecticides. These practices are especially compatible with high tunnel culture, which facilitates frequent harvest and good sanitation by allowing work in all weather conditions.
Education & Outreach Activities and Participation Summary
Participation Summary:
So far, outreach for this research has been primarily through giving tours and presenting talks. In the summer of 2018, one tour was led for a local Master Gardeners group, and two tours were led for participants of Penn State's Ag Progress Days, which included farmers as well as the general public. All of these tours included education about spotted wing drosophila, high tunnel raspberry production, and the rationale and design of this project. The rationale included discussion of the effects of UV-A light on different insect orders, visual demonstration of the attracticidal sphere technology, and explanation of how daily harvest interacts with SWD oviposition behaviors. Participants spent time in the tunnels seeing the experimental set up and treatments, and asking questions.
The two talks given on this research include a departmental seminar at Penn State University in November 2018 and a talk at the Mid Atlantic Fruit and Vegetable Growers Meeting in January, 2019. The departmental seminar reached fellow researchers, including those working in extension. It focused heavily on the data and analysis from the research and the implications for future research. The second talk primarily addressed small fruit growers, many of whom use high tunnels. This talk focused more on the practical applications of the research and on what the more theoretical aspects tell us about SWD management. This talk also had time to address grower concerns and questions. The Mid Atlantic Fruit and Vegetable Growers Meeting talk was accompanied by a proceedings article which provided a written version of the talk (Hershey-Proceedings). Many growers use the proceedings from the meeting for later consultation, so this article will be a reference for growers in the future.
A journal article is also being drafted covering this project as well as earlier SWD research we performed. This article is likely to be submitted to an entomology journal in 2019 with the hopes of publication. If published, this article will also be available on Tunnelberries.org, the website for the multi-state research project that our research was a part of. This website reaches growers looking for information on protected culture berry production, including structures, plastics, and pest control.
Project Outcomes
As our research is read more widely, it will contribute to agricultural sustainability in a number of ways. Primarily, our results clearly show that daily harvest and rigorous sanitation help reduce SWD infestation and increase yields. The reduction of yield loss is very important for overall sustainability, increasing yields without increasing inputs.
The second important finding is the compatibility of attracticidal spheres with high tunnel production. The spheres can significantly reduce both the amount of pesticides applied as well as the area they're applied to. Using attracticidal spheres is likely to reduce damage to beneficials, allowing growers to treat for SWD and still have natural enemies to help control other pests like spider mites and aphids. The spheres' compatibility with high tunnel production is very important given the benefits of high tunnel systems for raspberries (season extension, decreased disease pressure).
Although being able to use UVO plastic as a control might have reduced insecticide use, the plastic is manufactured outside of the United States and would require energy inputs for transportation, possibly making it less sustainable in a lifetime analysis. Proving that it does not control SWD allows us to rule out a need to take this costly and potentially environmentally unsustainable approach.
It's unclear what the cost of attracticidal spheres will be once they are commercially available, but they may provide an economic benefit compared with conventional sprays. The increased proportion of marketable fruit from daily harvest is economically important, resulting in significantly more fruit that a grower can sell. Again, proving that UVO plastic does not control SWD means that growers should continue to buy less expensive plastics, saving money.
This project intensified my interest in integrated pest management. I gained an appreciation for integrating insect behavior and phenology with control approaches. It also taught me a valuable lesson about keeping hypotheses simple and direct. I believe we proved useful points about how sustainable control may require many concurrent low-impact interventions, but I believe our approach was too complicated to get at basic biological questions regarding SWD behavior.
My experience with this project pushed me to apply for a PhD program working on IPM in the Hamby lab in the University of Maryland's Entomology department. I'm excited to begin doing work in field corn, researching the multitrophic impacts of pyrethroids and neonicotinoid seed treatments. I'm interested in looking at how arthropod communities with different functions (pollinators, parasitoids, predators) are affected by these insecticides, with the goal of providing incentive to not treat prophylactically. I'm eager to do this work, and I believe that it would have been unlikely that I would have been accepted to do this work without my SARE project giving me the experience designing and carrying out my own IPM research independently.
I believe that part of the design that made this research successful was the high tunnel facility at Penn State. The high tunnel facility included 18 research-sized high tunnels (6 were used for this project). This allowed replicated research of different plastic treatments, which was a major benefit. Having many smaller tunnels to work with allowed us to have many different treatments and replication. Concurrent with the SARE-funded project there was also a project comparing 5 different plastic treatments and 2 different raspberry cultivars. However, despite this benefit, there were still challenges, such as only being able to replicate each treatment 3 times. Larger sample sizes would have made our results more powerful. Second, the tunnels were fairly close together (which was important for controlling variation), which may have resulted in "spillover effects" of the treatments from one tunnel to the next, although it is unclear if this happened. High tunnel research is usually quite challenging in terms of replication, and overall Penn State's facility for doing high tunnel research was a major driver in the success of this research.
I think there is room for future research based off of the work done with this project. I think the most logical next step would be to assess sphere-density and placement in the high tunnels. We found a significant effect from attracticidal sphere presence, but they did not eliminate infestation. I believe looking at different numbers of spheres per plant would be extremely valuable, especially given the ways that high tunnel raspberry production differs from the field (much taller, bushier plants, drier conditions, etc).
I also believe that because the active ingredient in the spheres is widely used in conventional spray management, it would be useful to further explore formulations. Because all tunnel plastics block visible and ultraviolet light to some extent, it may also be useful to research the longevity of the spheres' activity in the tunnel compared to in the field.
Finally, as we saw a significant drop in both adult and larval SWD over the course of our experiment, it seems important to better elucidate the impact of time on treatments. One approach could be to begin the daily harvest and sphere treatments prior to SWD detection, and then monitor infestation and adults. It seems possible that the sustained use of these treatments might prevent build up. A second approach could be examining the effect of heightened sanitation with the 3 times a week and no-spheres treatment while minimizing the potential for spillover (for example, by using tunnels that are far apart, rather than adjacent tunnels or tunnels just divided in half with insect netting). It would be interesting to separate spillover effects from the effect of rigorous sanitation over time. This could tell us whether we should put more focus on treatments like spheres and daily harvest, or simply sanitation.