Photo by ES Cropconsult
SWD damage on blueberries.
SWD damage on blueberries.
With few tools available for spotted wing drosophila management, research is making great strides in organic solutions.
Blueberries and other fruits are often plagued by spotted wing drosophila (SWD) and while growers have emergency labelling for control, other options need to be created to manage the fruit-loving pest and reduce crop losses.
Early successes are being witnessed through trials by E.S. Cropconsult and studies out of the Department of Horticulture at Oregon State University (OSU).
Jen McFarlane, berry IPM supervisor and assistant research coordinator and Allyson Kang, berry IPM supervisor, both with E.S. Cropconsult, explored the use of traps in three organic blueberry fields in the Fraser Valley in 2018.
“SWD is a devastating pest for organic and conventional growers, but there are currently few management options for organic growers when it comes to SWD,” McFarlane says. “The chemical options that they do have are not highly effective and have a limited number of spray applications per season.”
Unfortunately, this creates the perfect storm for SWD, in that without a rotational management program, if SWD take hold in a field, their population explodes once they have ripe fruit available.
To explore the effects of traps with lures, Kang and McFarlane placed 20 large, yellow multi-lure traps from Great Lakes IPM along one edge of each field to ensure high density. The traps were filled with Scentry SWD lures and a dish with a soap and water solution (for capturing the flies).
To monitor SWD pressure and gauge response to the Scentry lures, Contech SWD traps were baited with apple cider vinegar and positioned in specific areas of the field both near to and far from the Scentry-lured traps for comparison. Both types of traps were checked, had their solutions changed and had SWD numbers recorded weekly for the seven-week trial. Also, to assess SWD larval infestation levels, McFarlance and Kang collected ripe blueberries twice during the season.
“Since there is only one season of data collected so far, conclusions are not definitive,” Kang said, but added, “The mass traps did catch large numbers of SWD with the highest estimate of 10,000 SWD captured in one field over the course of the study. The trap and lure combination was found to be highly effective and may have drawn more SWD into the traps than to the surrounding fruit.”
While one of the three fields seemed to have lower SWD levels in traps around the yellow mass traps than in the comparison traps further away, the other fields did not have this result. To help understand causes, a potential follow-up project will look at the results and will also include mass traps placed in the hedgerow in order to reduce the risk of drawing more SWD into the berry fields.
Photo by ES Cropconsult
SWD Larva
SWD Larva
“More years of data in more fields will help to demonstrate trends and to confirm if mass trapping could be used as a management tool for SWD,” McFarlane says. “It’s too soon for any recommendations to be made for this particular management method, however, growers who are desperate to try something different are encouraged to test any tools that might be effective.”
Until such time as definitive conclusions are available, she recommends a multi-pronged approach because a single tool is unlikely to provide control for organic growers.
“It is important for different management tools such as physical, cultural and biological methods to be researched to find how organic growers can either delay or prevent SWD from entering fields in the early season and then keep the population levels low during the fruit ripening period,” she says. “It is an uphill battle, but there is currently a lot of research going into all areas of SWD management so hopefully the combined effort will help increase options for organic growers to manage this difficult pest in the future.”
Kang hopes a planned follow-up study will provide three more years of data and more conclusions with a focus on both organic and conventional blueberries. She believes favourable results in blueberries could be applied to raspberry, blackberry and cherry crops.
South of the border, Vaughn Walton horticultural entomologist with the Department of Horticulture at OSU, is leading work that started in 2017 as a project to create a control agent to coat fruit and repel SWD. One versions of the control agent failed miserably and actually attracted SWD. The project changed direction as a result.
Team member Valerio Rossi-Stacconi, also from OSU, notes that the latest version of the attractant the team created beat out all types of fruit tested in its ability to attract SWD.
SWD found this attractant product suitable for mating, egg-laying and food, so they did not always turn to fruit when it was available. The attractant went through extensive trials in 2018 on blueberries, grapes, raspberries, cherries and strawberries. The number of eggs laid in four different varieties of blueberries was reduced by an average of 68.9 per cent.
“It has a comparable fruit damage reduction [to] normal chemicals that are used on crops,” says Rossi-Stacconi. “It requires, over a 21-day period, a single application, which is a great advantage of costs.”
Plus, like McFarlane’s research, there are no insecticidal compounds in the OSU product, thereby eliminating environmental issues, potential fruit toxicity and worker exposure concerns.
Testing for SWD controls will continue and with the right solutions, the lines between organic and conventional are likely to blur. ■