A survey study conducted in southern highbush blueberries during the 2012-2014 seasons showed that spotted wing drosophila is present in all of the seven major blueberry-producing counties surveyed in Florida. Grower awareness and proactive management have played a major role in the reduction of SWD in most counties. Trapping studies conducted in southern highbush blueberries in both high tunnel and organic field operations in 2012 and 2013 showed that the basic plastic cup trap (without yellow color or yellow sticky card modifications) proved an effective trap for SWD when baited with apple cider vinegar. Bait evaluations showed however, that yeast-based baits were more attractive to SWD than vinegar-based baits. Yeast-based baits remain non-specific to SWD and attract many other fly species, making identification more labor intensive. Field-based efficacy trials identified effective tools for control of SWD in blueberries. These tools can be used in rotation as part of a resistance management program for SWD.
Florida is a major producer of early-season blueberries. Although acreage is considered small (~ 4,500 acres) the industry is highly valued due to high market prices when berries begin ripening as early as March. During 2011, revenues were estimated at about $70 million USD. Despite the apparent success of this industry, a newly introduced pest, the Spotted Wing Drosophila (SWD) is threatening its integrity. Since its debut in Hillsborough County in 2009, SWD has spread to 26 counties, 8 of which are major blueberry growing regions. SWD is also threatening small fruits in other areas of the southeast including Georgia, Mississippi, and North Carolina.
Similar to other vinegar flies, SWD oviposits its eggs under the skin surface of thin- and soft-skinned fruits where larvae remain during development. Unlike most vinegar flies that prefer damaged or decaying fruit, the female SWD has a serrated ovipositor at the base of the abdomen that allows her to lay eggs in healthy, ripening fruit. Damage from SWD causes depressed scars on the fruit and rapid degradation from larval development, rendering fruit unmarketable. Blueberry growers in Florida and the southeast are in desperate need of an effective management program to suppress the activities of this fly. The goals of this project are to study the distribution and abundance of this pest in key blueberry counties throughout Florida, to develop an effective monitoring technique for SWD, and to identify reduced-risk insecticides that can be used to manage fly population in blueberries.
Obj. 1: To survey SWD in various blueberry growing regions and counties throughout Florida – completion date 2014
Obj. 2: To develop an effective monitoring system for SWD
a) To determine the most attractive bait to SWD – completion date 2013
b) To determine the most effective trap design for capturing SWD – completion date 2013
Obj. 3: To evaluate female SWD oviposition behavior
a) To determine viability of the most grown blueberry species in Florida, Rabbiteye and Southern Highbush, for larval development – completion date 2012
b) To determine susceptibility of different berry maturity stages to SWD oviposition – completion date 2012
Obj. 4: To identify reduced-risk insecticidal tools to control populations of SWD – completion date 2012
Obj. 1. The survey study was conducted during year three on the same 14 farms in eight Florida counties as years 2012 and 2013 (Fig. 1). Only the 2012 survey included the southernmost county of DeSoto. Since no SWD were captured in year 2012 and no growers had reported issues associated with SWD in the area, DeSoto County was not included in years 2013-14. Traps were made with 0.95 L clear plastic cups with lids with eight to ten-1/4 inch holes along the sides of the cup. Traps were secured to the middle of blueberry bushes with twist-ties. Each trap was baited with 150 ml of apple cider vinegar (ACV) and a drop of odorless dish detergent. The detergent reduces the surface tension of the bait and is thought to reduce fly escape from the trap. Each location had between four and seven traps placed along the perimeter of the blueberry field and in the center. Traps were collected weekly for the duration of blueberry season until harvest was completed. Number of weeks at each location varied based on the length of the season. Male and female SWD were identified and counted at the UF Small Fruit and Vegetable IPM Laboratory in Gainesville, Florida. The mean number of SWD per trap was calculated for each county.
Obj 2 details are excerpts from Iglesias, L. E., T. W. Nyoike and O. E. Liburd. 2014. Effect of trap design, bait type, and age on captures of Drosophila suzukii (Diptera: Drosophilidae) in berry crops. J. Econ. Entomol. 107: 1508-1518.
Obj. 2a. The effectiveness of baits used to monitor SWD was evaluated in a commercial organic southern highbush blueberry farm in Citrus County. The experiment was conducted from 8 May to 27 May 2013. Four monitoring traps each baited with different bait treatments (discussed below) were placed at 20-m intervals in a randomized experimental design with four replicates. Traps were placed within the center of the field. The traps were hung in the shaded areas of the shrub canopies. Four bait treatments were evaluated: 1) apple cider vinegar (ACV), 2) yeast + sugar mixture, 3) yeast + flour mixture (yeast, whole wheat flour, ACV, sugar, water, detergent, and 4) wine + vinegar [red grape wine, rice vinegar, and detergent] (Fig. 2). Our wine + vinegar bait was based on a 60:40 mixture of Merlot red wine and rice vinegar with the addition of detergent (Landolt et al. 2012b). Our bait consisted of concentrated rice vinegar (25% acetic acid) whereas Landolt et al. (2012b) used diluted vinegar (4%), resulting in a bait with lower acetic acid concentration. All baits were evaluated using the basic plastic cup trap as described in the survey study. Samples were collected weekly.
The studies were conducted at a commercial high-tunnel and field locations in 2012 and 2013 in Alachua and Citrus County, respectively. In 2012, five trap designs (treatments) were evaluated, all baited with ACV. One trap was a yellow PheroconAM sticky card (15.2 by 20.3 cm) used for monitoring apple maggot and other flying insects (Great Lakes IPM, Vestaburg, MI). The other four traps were handmade from 0.95-liter clear plastic deli cups with lids (Solo, Urbana, IL) and each container had ten 0.64-cm holes along the upper rim. Modifications of the plastic deli container (basic cup trap described above), included the addition of a small (7.6 by 7.6 cm) yellow sticky card (Great Lakes IPM, Vestaburg, MI) hanging inside to prevent flies from escaping and to act as a visual stimulus, a yellow visual stimulus band (30 cm in width by 4.5 cm in height foamboard) wrapped around the inside middle of the cup, and odorless dish detergent (Palmolive Pure and Clear, Colgate-Palmolive Company, New York, NY). Therefore, the five trap treatments were as follows: 1) basic cup, 2) cup + yellow stimulus band, 3) cup + yellow stimulus band + detergent, 4) cup + yellow sticky card inside, and 5) yellow sticky card (noncup trap). Cup traps were baited with 150 ml of ACV. The Pherocon AM yellow sticky card was baited with a 7.4-ml glass vial (Fisher, Pittsburg, PA) containing ACV. Bait was released through the 1-cm hole on the top of the vial. In 2013, the Pherocon AM yellow sticky card was omitted based on the low captures from 2012. In addition, the cup trap with the yellow stimulus band modification around the inside middle of the cup (without detergent) performed similar to all other cup traps in 2012 and was also omitted. The four trap treatments evaluated were as follows: 1) basic cup trap (described above), 2) cup + yellow stimulus band + detergent, 3) cup + yellow sticky card inside, and 4) cup + yellow sticky card inside baited with a 150 ml yeast + sugar mixture (Fig. 3). All other traps were baited with 150 ml ACV.
Obj 3a. During year one, we conducted a laboratory no-choice bioassay to look at the suitability of two common blueberry species, Southern Highbush and Rabbiteye, for SWD larval development. Two berries were exposed to 10 females for 96 hours (16 replicates). After 14 days, adult emergence was counted daily for 1 week.
Obj. 3b. We conducted a laboratory choice bioassay to examine the susceptibility of different ripeness stages of Southern Highbush blueberry. Treatments were green, green-pink, pink, pink-blue, and blue. Two branches were placed in each bioassay chamber (28 replicates) and 10 female flies were introduced for 72 hours. Females were observed for 5 minutes daily, ovipositing females counted and berry color noted. Female was considered as ovipositing when the ovipositor was inserted into the skin of the berry.
Obj 4. The experiment was conducted in two phases between April 9 and 24, 2012. The experimental design was a randomized complete block with 7 treatments and 4 replicates. Treatments consisted of 3 conventional pesticides, Danitol® at 10.333 oz/acre (Dan10.3, Fenpropathrin, Valent Corp., Walnut Creek, CA), Danitol® at 16 oz/acre (Dan16), and Mustang® at 4 oz/acre (Mus4, zeta-cypermethrin, FMC, North Carolina), 3 reduced-risk pesticides, Belay® at 4 oz/acre (Bel4, Clothianidin, Valent Corp., Walnut Creek, CA), Belay® at 6 oz/acre (Bel6), and Delegate® at 6 oz/acre (Del6, Spinetoram, Dow AgroSciences, Indianapolis, IN), and a water treated control (Cont). Mustang Max® and Delegate® treatments were added to provide a comparison of all treatments to industry standards. One day after application (DAA), two branches were selected from blueberry varieties and transported back to the University of Florida, Small Fruit and Vegetable laboratory in Gainesville. One branch from each variety was placed into a bioassay (treatment) chamber for males and the other two branches into a chamber for females.
Adult activity measurements began 24 hours after the flies were introduced into the bioassay containers. Data were taken by picking up the container and gently tapping the sides to elicit an activity response from the flies. Fly activity was measured on a scale of 0 to 3, using methods described in Liburd et al. (2003). A score of 3 indicated unaltered fly activity (fly in its natural state). A score of 2 indicated decreased responsiveness to tapping. A score of 1 indicated responsiveness to tapping and a general inverted, twitching appearance. Fly death was designated a score of 0. Containers were observed for 5 minutes to determine mortality. Data were collected as number of flies in each category (0 through 3). The values were then weighted based on their categorical number and averaged by the number of responding flies in each container (some flies died due to berry drop).
2014 Results: We found that SWD was present in all counties, which confirmed our findings from 2012 and 2013 (Fig. 4). Mean SWD captured per trap per week were similar in most counties. However, Citrus County had a higher number of captured SWD than Lake County (F = 3.00; df = 6, 344; P = 0.0072).
Overall 3-Year Results: The mean SWD captured per week per trap in 2012 was significantly higher than in 2013 and 2014 (F = 16.22; df = 2, 1574; P < 0.0001). Spotted wing drosophila captured between 2013 and 2014 were similar. There were a total of 844, 498, and 341 SWD captured in 2012, 2013, and 2014, respectively. There were significant differences in SWD captures among counties in 2012 (F = 22.02; df = 8, 584; P < 0.0001), 2013 (F = 2.52; df = 7, 645; P < 0.0001), and 2014 (F = 3.00; df = 6, 344; P = 0.0072; Table 1). Citrus County had the highest mean captures in 2012 (4.81 ± 0.31). Marion County (1.44 ± 0.37) and Alachua County (1.34 ± 0.20) were significantly higher than Orange (0.53 ± 0.17) and Suwannee County (0.05 ± 0.49) in 2013. Citrus County had higher captures than Lake County in 2014 (3.07 ± 0.83). Small differences were found when evaluating differences between years for each county. Alachua County had higher captures in 2012 than in 2014, whereas captures in 2013 were similar Citrus County had significantly higher SWD captured in 2012 compared with 2013 and 2014. In Lake County, more SWD were captured in 2013 than in 2014. In Marion County there were significantly more SWD captured in 2013 compared with 2012. Orange County saw significantly more SWD in 2012 than in 2013 and 2014. Polk County had an increase in SWD captured from 2012 to 2014. The mean SWD captured in Putnam and Suwannee Counties remained similar throughout the 3-year survey.
Discussion: Differences between SWD captures in years 2012-2014 may be due to temperature differences between the years. Weekly mean temperatures averaged below 20°C until the first week in May 2013; conversely during the early part of 2012 temperatures averaged between 20 and 23°C. The SWD has shown decreased activity at temperatures below 20°C and above 25°C (Kanzawa 1935, Kimura 2004). Additionally, growers had become aware of the risk posed by SWD after the survey in 2012 and were proactive in implementing management programs for this pest in 2013 and 2014. Further statewide surveys will help to answer whether the current management programs are effective at reducing SWD populations to the next season.
Spotted wing drosophila captures varied by county. The highest mean captures were in the central (Citrus Co.) and north-central (Alachua Co.) parts of the state. Citrus County has a large number of organic blueberry growers, who are limited in the available control options available for this fly. Secondly, several growers in Citrus County grow strawberries adjacent to blueberries. Strawberries are a known host of SWD and the crop seasons overlap to a limited extent in the field. If SWD is established in strawberries the pressure on blueberries is likely to be greater. Alachua County has the highest acreage of blueberries in high tunnels in Florida. The tunnels act as greenhouses, creating artificial warm environments that could promote SWD development early in the season. It is unknown whether the risk to blueberries in high tunnels is greater than field-grown blueberries but this warrants further investigation.
Obj 2 details are excerpts from Iglesias, L. E., T. W. Nyoike and O. E. Liburd. 2014. Effect of trap design, bait type, and age on captures of Drosophila suzukii (Diptera: Drosophilidae) in berry crops. J. Econ. Entomol. 107: 1508-1518.
Results: Results from the blueberry bait study showed significant differences among the bait treatments [F = 13.76; df = 3, 11.99; P = 0.0003] (Fig. 5). Both yeast + flour and yeast + sugar baits had significantly greater mean SWD captures than ACV and the wine + vinegar mix. Captures of male and female flies did not differ significantly in any of the treatments.
The baits also attracted other dipteran species, specifically the recent invasive Zaprionus indianus Gupta (Drosophilidae) and other non-target flies in the family Drosophilidae (excluding SWD and Z. indianus). The number of Z. indianus captured was significantly greater in the yeast + flour mix than all other bait treatments [F = 8.85; df = 3, 11.93, P = 0.0023] (Fig. 6). Significantly more non-target drosophilids were captured in the yeast + flour mix than in the trap with ACV or wine + vinegar (F = 13.42; df = 3, 12.23, P = 0.0004). The yeast + sugar bait was not significantly different than any of the other baits.
Discussion: The results showed that the yeast baits (yeast + sugar and yeast + flour) were more attractive than the vinegar baits (ACV and wine + vinegar) which are similar to other studies (Dreves et al. 2012, Walsh et al. 2011). However, the yeast-based baits were highly attractive to other drosophilids, making identification more difficult and time consuming. The vinegar and wine baits on the other hand, are generally clear or can be easily rinsed from specimens and permit quick identification in the field or laboratory. The vinegar and wine baits also act as excellent preservatives for collected specimens. The big disadvantage is that SWD captures may be slightly lower than yeast-based baits and may not be effective where populations are low. Unless a specific bait for SWD is developed other vinegar flies and small non-targets will likely be found in SWD traps.
Results 2012: Treatment had a significant effect on the mean spotted wing drosophila captured in the high tunnel (F = 4.26; df = 4, 15; P = 0.0168) and in the organically managed field (F = 6.34; df = 4, 15; P = 0.0034; Fig. 7). The Pherocon AM yellow sticky card did not capture any spotted wing drosophila in either experiment. The basic cup trap, cup + yellow stimulus, and cup + yellow stimulus + detergent captured significantly more spotted wing drosophila than the Pherocon AM yellow sticky card in the high tunnel blueberries. The cup + yellow sticky card inside was not significantly different from the Pherocon AM yellow sticky card. All of the cup treatments captured significantly more spotted wing drosophila than the yellow sticky card. There were no significant differences among the four cup treatments in either experiment. Overall, the high tunnel and organic field showed similar trends for mean spotted wing drosophila captured among treatments.
Results 2013: Treatment had a significant effect on SWD captures in the high tunnel (F = 6.18; df = 3, 12; P = 0.0088) and the organically managed field [F = 6.490; df = 3, 12; P = 0.0074] (Fig. 8). In the high tunnel, the yeast-baited cup + yellow sticky card inside captured significantly greater number of SWD than the ACV-baited cup + yellow stimulus and the basic cup trap. However, the ACV-baited cup + yellow sticky card was not significantly different than any of the other trap treatments. In the organically managed field, the yeast-baited trap captured significantly more SWD than the ACV-baited cup + yellow sticky card and the basic cup trap whereas the ACV-baited cup + yellow stimulus was not significantly different than the other traps. No significant differences in number of females and males captured were observed in any of the traps in 2013.
Discussion: Our findings indicate that neither the yellow visual stimulus nor detergent increases SWD captures when using the basic cup trap (0.95-liter clear plastic deli containers with lids) baited with apple cider vinegar (ACV). The modified ACV-baited traps (yellow visual stimulus band, yellow sticky card, and detergent) were not significantly different from the basic unmodified ACV-baited trap in either year. The result is consistent with previous findings that the color yellow does not increase ACV-baited trap captures of SWD (Lee et al. 2011 and Basoalto et al.2013). In our 2013 trap comparison study, the trap with the yellow sticky card and the yeast + sugar captured significantly more SWD than the same trap baited with ACV in the organically managed blueberry farm. These results suggest that the type of bait is a more important factor in attracting SWD flies than the trap design modifications tested. The yellow sticky card may catch a few SWD; however, this tends to complicate matters since identification of SWD on the card can be difficult. We noticed that specimens captured on the cards tend to desiccate rapidly, requiring immediate identification, whereas flies captured in the ACV drowning solution maintained their color and overall appearance. This is an important finding since additional time would be required by growers to insert yellow foamboards or yellow sticky cards with the hope that this tactic will increase the effectiveness of the trap in detecting SWD. The addition of detergent is also a common practice thought to improve SWD captures. However, our results indicate that the detergent could be omitted and the efficacy of the trap system would remain unaffected, reducing the time and cost of constructing the traps.
Objective 3a, b
3a Results: The mean number of SWD that emerged from the RE blueberry species was 0.56 ± 0.18 per berry compared with 1.03 ± 0.18 from SHB blueberries (Fig. 9). Although SHB blueberry appeared almost two times more suitable than RE, the data were not significantly different (F = 3.02; df = 1, 24; P = 0.10). The effect of berry maturity (ripening) stage was highly significant (F = 9.25; df = 3, 24; P = 0.0003; Fig. 10). The mean emergence from blue berries was significantly higher than all other stages. No differences were found among the other stages. Additionally, color*blueberry species interaction effects were not significant (F = 0.36; df = 3, 24; P = 0.79).
Results: Overall, the mean number of oviposition events per observation for all treatments was low. We found that 78 percent of females oviposited on blue berries, 17 percent on green, 5 percent on pink, and none on pink-blue or green pink (Fig. 11). Female SWD was 4.7 times more likely to oviposit on blue than green berries.
Discussion for Obj. 3a, b: The results suggest that both species of blueberries grown in the southeastern U.S. are susceptible to infestation by SWD. Southern highbush blueberries appear 50% more suitable than RE blueberries (P = 0.10). It is likely that there are unique characteristics of RE blueberry that make it different from SHB (grittier texture, firmer skin, and larger seeds) and therefore, may play a role in host suitability. Additionally, SWD will oviposit on earlier ripening stages including immature green berries. Blue berries appear to be the most susceptible stage but growers should begin their management programs (monitoring and spraying) early in the season when berries are full green since flies are capable of ovipositing in these berries. Other studies suggest that though SWD is capable of ovipositing in green berries, larval development will be reduced (Lee et al. 2011) and therefore, larval survivorship should be included in subsequent studies.
Results: There was a significant treatment effect on SWD activity on 1 d (F = 8.14, df = 6, 47; P < 0.0001), 3 d (F = 2.21; df = 6, 47; P = 0.05), and 7 d post-treatment (F = 2.49; df = 6, 47; P = 0.04; Table 2). On 1 and 3 d, Delegate®, Mustang Max®, Danitol® high, and Danitol® low significantly reduced SWD activity level below the control. On 7 d, Danitol® high and Danitol® low significantly reduced SWD activity below the control. There were no significant differences between the control, Belay® high and Belay® low on any of the days post-treatment. Additionally, SWD activity was reduced equally in both high and low rates of Danitol®.
Discussion: Our study identified effective insecticides for SWD management. Results indicate that Mustang Max®, Delegate®, and Danitol® high and low rates were effective at reducing SWD activity up to 3 d residual. After 7 d residual, Danitol® at the high and low rates was more effective than Mustang Max® and Delegate®. In addition, no significant differences were found in SWD activity between the high and low rates of Danitol® suggesting that the low rate would be an effective alternative tool for controlling SWD in the field. The chemicals identified are in different classes – Mustang and Danitol are pyrethroids and Delegate is a Spinosyn – and therefore could be used in a rotational resistance program. Additionally, Danitol and Delegate have longer preharvest intervals (3 d) and would be used before peak harvest when SWD populations are beginning to increase. Mustang and the commonly used Malathion have short preharvest intervals (1 d) and would be applied during peak harvest. The results of our study identified effective tools that can be recommended for use in a rotational program against the spotted wing drosophila.
- Figure 6: Mean Drosophilidae and Zaprionus indianus captured per trap per week in the 2013 bait experiment.
- Figure 7: Mean SWD captured per trap in the high tunnel and organic field 2012 trapping experiments.
- Figure 11: Total SWD ovipositing on different blueberry ripeness stages.
- Table 2. Mean activity level per fly between treatments within each day after application.
- Table 1. Mean number of SWD captured in each county in the 2012-2014 survey study.
- Figure 5: Mean SWD captured per trap per week in the 2013 bait experiment.
- Figure 8: Mean SWD captured per trap in the high tunnel and organic field 2013 trapping experiments.
- Figure 9: Mean emerged SWD in rabbiteye and southern highbush no-choice oviposition experiments.
- Figure 10: Mean SWD emergence from different berry maturity stages in no-choice tests.
- Figure 4: Mean SWD captured per trap per week in blueberries in Florida counties in a survey conducted in 2012-2014 seasons.
Educational & Outreach Activities
Iglesias, L.E. 2013. Integrated management strategies for spotted wing drosophila, Drosophila suzukii, in southern highbush blueberries. Master thesis submitted to University of Florida, Florida.
Liburd, O. E. and L. E. Iglesias. 2013. Spotted wing drosophila: pest management recommendations for southeastern blueberries, ENY869. University of Florida, Institute for Food and Agricultural Sciences (IFAS) and Florida Cooperative Extension Service. Gainesville, FL. http://edis.ifas.ufl.edu/in998
Peer-Reviewed Journal Article:
Iglesias, L. E., T. W. Nyoike & O. E. Liburd. 2014. Effect of trap design, bait type, and age on captures of Drosophila suzukii (Diptera: Drosophilidae) in berry crops. J. Econ. Entomol. 107: 1508-1518.
Liburd, O.E., L.E. Iglesias, and T.W. Nyoike. 2014. Integrated pest management strategies to combat the invasive spotted wing drosophila, Drosophila suzukii (Matsumura) Diptera: DrosophilidaeWorkshop in Gainesville. In Proceedings, 12th Annu. North American Blueberry Research and Extension Workers Conference (NABREW), 23-26 June 2014, Atlantic City, NJ. Sheraton Atlantic City Convention Center Hotel. Rutgers University. (in press)
Workshop with ID materials:
Fruit Growers Workshop, Straughn Extension Center, Alachua County, FL 2014
Approximately 80 growers from the state of Florida and Georgia attended the workshop. A presentation was given detailing the current state of SWD in blueberries and information on SWD identification. A hands-on workshop followed focusing on ID of SWD and explanation of recommended monitoring traps and baits. Materials were created for identifying SWD and were provided at the workshop (Fig. 12).
Farmer awareness: Drosophila suzukii has been in Florida since at least 2009, when it was first detected. Statewide surveys for the pest had not been conducted to determine its range throughout the state. Small fruit growers in the state were not monitoring for SWD and had not been concerned with losses until 2012. The results of the 2012 SWD blueberry survey came as a surprise to most growers in the state and raised awareness for the potential of this fly to establish itself in areas of cultivated crops. Losses of approximately 10-15% were being reported, a large portion of that by organic blueberry growers. By 2013, some growers had begun monitoring regularly but most were reliant on the survey work done by our lab. Also, growers began to establish control and sanitation protocols for SWD throughout the blueberry season. Our 2014 survey results showed that those growers who maintained intense control and sanitation protocols were able to reduce SWD populations and losses. In addition, many more growers have their own monitoring programs established on their farms.
Better monitoring programs (traps, baits, timing): Many growers have established their own monitoring programs for SWD. When the first survey was conducted in 2012. The monitoring tools (traps and baits) were the best available based on our most recent research. Our trapping studies showed that basic traps can be constructed by the grower, reused for multiple seasons, and are relatively inexpensive to construct. Our bait studies supported the use of a more effective bait (yeast sugar mixture) than the commonly used apple cider vinegar. The yeast mixture captures more SWD and captured them sooner in the season than the other vinegar baits tested. Furthermore, the oviposition studies indicated that SWD will attack unripe berries and therefore the best time for beginning monitoring programs for this fly is when the berries begin to turn from green to pink. Growers have incorporated these new effective tools into their monitoring strategies with success.
New tools: The efficacy studies conducted identified new, effective tools for the control of SWD in blueberries. Danitol (pyrethroid) and Delegate (spinosyn) are effective up to 7 d and have longer PHI of 3 d. These can be used in rotation before harvest begins. Mustang, a pyrethroid, is effective up to 7 d and has a short PHI of only 1 d. This tool can be used in rotation with Malathion (an organophosphate) during times of peak harvest. All growers have taken advantage of the few new chemicals identified that will aid in the control of SWD. Many growers have reported the success of these products to date. We will continue to investigate new options of control including cultural controls and reduced risk insecticides to prevent the buildup of resistance.
By the second year of our study, some growers were beginning to monitor regularly on their farms but most were still reliant on the survey work done by our lab. Also, growers were also beginning to establish control and sanitation protocols for SWD throughout the blueberry season. By the final year of our study, those growers who maintained intense control and sanitation protocols were able to reduce SWD populations and losses in their blueberries. Currently, many more growers have established their own monitoring programs on their farms and are able to identify SWD on their own. Our lab is still active in identifying and confirming reports of SWD captured in monitoring traps throughout the state.
Growers have adopted the new monitoring tools (traps and baits) based on our most recent research. Our trapping studies showed that basic traps can be constructed by the grower, reused multiple seasons, and are relatively inexpensive to construct. Our bait studies supported the use of a more effective bait (yeast sugar mixture) than the commonly used apple cider vinegar. The yeast mixture captures more SWD and captured them sooner in the season than the other vinegar baits tested. Furthermore, the oviposition studies indicated that SWD will attack unripe berries and therefore the best time for beginning monitoring programs is as the berries begin to turn from green to pink. Growers are able to detect SWD in the fields when populations are low and before berries become ripe. Growers have incorporated these new effective tools into their monitoring strategies with success. Growers have also adopted the recommended new, effective tools that can be used in a rotational program against SWD in blueberries.
- Begin monitoring programs early. Based on the results of the oviposition study, female SWD will oviposit in unripe fruit. This suggests that SWD will migrate into the field before peak harvest and build populations to potentially devastating levels. Traps should therefore be established as the berries begin to turn from green to pink. Setting traps early allows for early detection and control of SWD before populations become unmanageable.
- Use a simple clear plastic container with 10-12 holes along the rim for trapping SWD. Our results indicated that the addition of neither a yellow band nor a yellow sticky card inside the trap increased the number of SWD captured. The additions increase time of construction and identification and the cost of constructing the trap.
- Use a yeast sugar mixture for trapping SWD if time permits. Our studies revealed that yeast mixtures were significantly more effective at capturing more SWD and capturing them earlier in the season. However, the yeast bait makes identifying SWD more difficult. Samples can be rinsed with water prior to identification to reduce time.
- Practice sanitation. Fallen and overripe fruit should be removed from the ground and bushes as SWD may be developing inside overripe or damaged berries. Berries should be destroyed by solarization or burial.
- Develop a rotational program for control of SWD using insecticides from different classes and preharvest intervals. Effective tools have been identified for control of SWD including those from the pyrethroid, spinosad, and organophosphate classes. Insecticides with longer PHIs should be used before harvest to prevent the explosion of SWD in the field and those with shorter PHIs should be used during harvest.
Areas needing additional study
- Organic products – New tools are being developed frequently for use in conventional cropping systems. However, organic growers are limited to two insecticides – spinosad and pyrethrin. Pyrethrin has been shown to be ineffective at controlling SWD populations whereas spinosad, an effective compound, has a longer PHI of 3 d. The PHI of 3 d prevents the use of this product during times of peak harvest when berries are being picked every 2-3 d.
- More specific traps and baits – Much research has been published on the topic of attractants for SWD trapping, mostly focused on food-based baits (Iglesias 2013, Kleiber 2013; Landolt et al 2012a, b) and the volatile chemistry of the host fruits (Cha et al. 2014) and their associated yeasts (Becher et al 2012, Hamby et al 2012). The color of traps can be easily modified to increase their attraction to the specific pest they are designed to catch (Liburd et al 1998). However, the observation of color depends on the light, viewing angle, and viewer. Further research will be conducted that investigates the role that spectral reflectance plays in SWD attraction to and oviposition preference for host fruits.