We are continuing to receive samples and reports of spotted wing drosophila, or SWD, damage to blackberries from central and western Kentucky.
The common description is soft, mushy berries that deteriorate very quickly and contain small white larvae. In some commercial plantings the damage is severe with producers reporting nearly a complete loss of the fruit.
Some producers have been unsatisfied with the level of control after using sprays for SWD. There can be several factors that can contribute to this. First, the sprays targeting SWD are to control the adults. The eggs and larvae already in the fruit are not controlled. So after spraying it may take a week to 10 days for the larvae already infesting the fruit to cycle through.
Additionally, many producers may have been caught by surprise and were late to begin their protective sprays and, as a result, had very high populations of SWD adults when they began spraying.
Fall raspberries threatened
Producers of fall raspberries are at high risk of SWD infestation. They should plan on using trap for detection of SWD adults. If any detection is made, sprays for SWD control should begin immediately and reapplied at 5- to 7-day intervals.
Heavy rainfall may require reapplication of sprays. I would recommend they look at the recommended insecticides for SWD control and have at least one of those materials on hand. Producers should also plan to rotate to a different mode of application with each subsequent application.
Timing, coverage and selection of the correct insecticide are important with any insect pest, and this is the case with SWD. The adults prefer to stay in the darker, denser part of the plant canopy. The same place where getting thorough coverage will require higher pressure and spray volume.
Keep it clean
Homeowners and commercial growers are encouraged to use clean harvest techniques to help slow the population buildup of SWD. Damaged, overripe, and infested fruit should be collected and removed from the field when practical. These fruit can be placed in a clear plastic bag and left in the sun for a couple of days to solarize and kill any potential SWD.