Samples this past week indicate that spotted wing drosophila (SWD) activity is increasing across the state with numbers of these captured insects considerably higher at some locations. While the threshold to begin management is ‘one captured fly,’ continued trapping provides information on relative activity and effectiveness of the management program. Simply determining if the population is increasing, decreasing, or staying the same can be very helpful.
In addition to using the SWD traps to capture adults, we also recommend sampling ripe undamaged fruit for larvae. Simply place about 20 berries in a sealable bag, and then add two cups water and 1/2 cup sugar. Mash the berries and look for the 1/8- to 1/4-inch white larvae floating to the surface.
In terms of insecticide applications to manage these insects, once SDW have been captured on a farm (or if the farm is not trapping), consider beginning sprays at the first capture or a week before the start of the harvest period. Reapply sprays on a weekly basis. When there is a significant heavy rainfall event, a new spray may be needed. Producers need to rotate among modes of action with subsequent sprays and follow pre-harvest intervals (PHIs) carefully.
Ric Bessin, Extension Entomologist