Despite the lingering cool weather, spring is upon us, and fruit set is underway with plasticulture strawberries. This is the first of the spotted wing drosophila (SWD) susceptible crops, which also include blueberries, blackberries, raspberries, cherries, and grapes. Last year, many producers noted that SWD infestations did not appear to be as bad as they were during 2013. I don’t know if this was due to lower population levels or because producers were better prepared to manage SWD. Despite lower levels, this is a threat that requires monitoring, and producers should be prepared to manage SDW as needed.
While spotted wing drosophila can be a serious pest of strawberries in southern or western regions of the country, we have not seen SWD activity in Kentucky until after the harvest period of June bearing strawberries is complete. That being noted, we only have 2 years of experience managing SWD in Kentucky, so I encourage strawberry producers to monitor for SWD before and throughout the harvest period with adult traps.
The trap (Figure 1) we are recommending is a clear 1-liter deli container, with two 3 x 1.5-inch windows cut in the side and plastic screening glued in place. Each trap should contain about ½ cup apple cider vinegar; add one drop of dish soap as a drowning solution. On the inside of the lid, hang a commercial SWD lure to attract the flies. The lure only needs to be replaced monthly; used lures should not be disposed of in the field.
Identifying Spotted Wing Drosophila
Many different types of flies and species of drosophila are captured in these traps. To identify SWD, the flies should be poured into a light colored pan and examined with a hand lens. The males (Figure 2) are recognized by the single black spot on each wing.
The female SWD (Figure 3) has a hardened and enlarged ovipositor (egg layer), amber body color, and continuous dark banding on the abdominal segments.
The threshold for treatment is one trapped SWD on a farm. If SWD is not trapped, then sprays for SWD are not necessary. However, when SWD is captured, weekly sprays are recommended on susceptible crops during the harvest period. See the publication Spotted Wing Drosophila Management (ENTFACT-230) for recommendations.
This summer, cooperators in about 22 Kentucky counties will be trapping for SWD in various small fruit crops. Results will be posted weekly on the SWDinKY Facebook website.
By Ric Bessin, Extension Entomologist