Spotted wing drosophila (SWD) is in high numbers in many parts of the state and has overwhelmed control efforts in some areas. Fall red raspberry (Figure 1) harvest is underway and some growers have not been able to get adequate control. In addition to the problems with damaging fruit in the field, SWD can also become a nuisance pest of farm markets; adults are attracted to the harvested fruits and/or are emerging from infested fruits. I have had reports of producers not able to get control when using the recommended insecticides, so in this article I address the strategies to get the best possible control.
Management in Plantings
- Trap for SWD and begin spraying when the first adult is detected and the fruit are within 10 days of harvest. Sprays are meant to target SWD adults before they have a chance to lay eggs. Once eggs are laid under the skin of berries, we cannot kill the egg or the larvae inside the fruit with insecticides. Only use recommended SWD insecticides at the proper rates; refer to Spotted Wing Drosophila Management (ENTFACT-230).
- Use a high pressure sprayer and water volume high enough to get thorough coverage inside the canopy. Water sensitive paper can be placed inside the canopy to ensure coverage is thorough.
- Prune canes to allow for excellent spray coverage. SWD adults avoid sunlight and hide in the darkest part of the canopy during the day, so proper canopy management enhances spray penetration and reduces shelter for the adults.
- Reapply sprays after rains. Experience in other states has shown that intense rains, like those we have experienced this summer, can ruin residual control with SWD sprays.
- Never go more than 7 days between sprays. With fall raspberries, plants may be blooming during the harvest period (Figure 2), so producers must protect pollinators by spraying when pollinators are not active.
- Don’t leave overripe or damaged fruit in the field (this is very difficult to do, but incredibly helpful). Bag fruit for disposal in clear plastic and leave in the sun. Burying the fruit is not effective.
- Switch modes of action regularly. SWD can complete a generation in just over a week at the ideal temperature. Modes of action need to be switched weekly.
- Refrigerate berries as soon as harvested; the closer to 32 degrees F, the better.
Management at On-farm Markets
In on-farm markets, SWD can also be a nuisance and impact customer satisfaction and sales. Market stores need to pay attention to breeding sites for SWD in and around the outside of the buildings. As with other fruit flies, sanitation is very important.
- Damaged, overripe, and other culled produce for disposal need to be removed promptly and placed into sealed bags.
- Trash cans should have liners and be emptied regularly.
- Fruit fly traps in markets can be used to identify hot spots.
- Produce not on display should be stored in a cooler.
- Do not place cull piles or neglect management of susceptible crops near on-farm markets.
By Ric Bessin, Extension Entomologist