Figure 1. Male spotted-wing drosophila on a blueberry. Note males have spots on wings, as pictured here, but females lack spots on wings. Photo credit: T. Martinson
For those growing delicious small fruits, including cherries, raspberries, blackberries, blueberries, and strawberries, on a U-pick farm or even your backyard, now is the time to be on the lookout for spotted-wing drosophila (SWD), especially if your berries are ripe or in the ripening stage.
Most of you are likely familiar with SWD (Figure 1), we wrote a couple of articles in Facts for Fancy Fruit last year; but just as a reminder, SWD is an invasive vinegar fly that looks a bit like the fruit flies you might see hovering around your ripe bananas or apples in the kitchen. However, two key differences are: 1) SWD is attracted to small fruits as they begin to ripen, and 2) female SWD have a specialized egg-laying organ that allows them to cut into healthy fruits and lay eggs. So, these flies have the potential to damage sound berries and make them unmarketable by laying eggs under the skin that hatch into small maggots that will feed on the fruit, reducing berry quality and disgusting customers – unless they are fans of entomophagy (the practice of eating insects as food!).
Figure 2. Commercially available Scentry monitoring trap for Spotted-wing drosophila, available from Great Lakes IPM.
There are several effective and relatively inexpensive monitoring tools for SWD that include a pheromone lure hung inside a red container filled with water or apple cider vinegar solution (Figure 2). The lure in these monitoring traps attracts SWD and when they enter the container, they bump around and eventually fall into the liquid and drown – making them easier for you to detect! By collecting and examining the flies in the drowning solution once a week, you’ll know when SWD first appears in your orchard and be able to make an informed decision about when to begin management strategies for this important small fruit pest. We are monitoring SWD in blueberries in three locations in Indiana this summer: Warrick, Tippecanoe, and Starke County and we will share results of trap activity as we have it in real time on the Long Lab website (https://extension.entm.purdue.edu/longlab/extension/#reports). So far, we haven’t detected SWD in blueberry crops, but as the berries ripen, temperatures rise, and the season progresses, it is only a matter of time before they appear.
The current recommendation is to begin spray schedules for SWD when a single fly is detected in the trap AND berries are ripening on plants. By using monitoring traps, you might save money by holding back on early sprays targeting SWD before they are present in your small fruit orchard. Finally, it is critically important to evaluate how well your spray program is managing SWD in your small fruit orchards. If you are spraying on a 7-10 day schedule and continue to see berries with maggots or significant reductions in berry quality, this may be a sign that the insecticides you are using are not mixed properly or are not at the correct rate, or that your sprayer equipment needs adjustment or other attention.
You can find more information about SWD management strategies and insecticide options for vulnerable fruit crops in the 2021-2022 Midwest Fruit Pest Management Guide. As always, if you have questions about SWD identification or how to place and use monitoring traps, reach out to your local extension educator or specialist so we can help!