Spotted wing drosophila (SWD) activity is beginning to increase with positive samples identified from several western and southern Kentucky counties, as well as from one in central Kentucky (Figure 1). We are still collecting mostly negative samples from central and eastern Kentucky counties.
Although we began trapping SWD in mid-May (10 days earlier than last year), activity has been increasing slowly until this past week. For the most part, the numbers captured have remained relatively low in locations SWD has been found. In 2015, SWD captures remained low until the start of blackberry harvest, at which point they increased rapidly. Up until now, that pattern is holding with relatively low numbers in the few locations where we have found them. The exceptions are Caldwell and Trigg Counties, where numbers have been higher.
In fields where we have SWD traps (Figure 2) but have not detected SWD, the risk is very low. However, even if a single SWD is trapped in a field, producers are advised to spray for SWD weekly during harvest to minimize the risk of an infestation to berries. Because these crops are picked several times per week, producers are restricted to insecticides with short pre-harvest intervals (PHIs).
In addition to insecticidal protection of berries when SWD is active in a field, immediate post-harvest cooling of picked berries is also very important to arrest the development of eggs and larvae. Those growing small fruit at home can also use fine netting to exclude SWD flies from plantings. Nets can be draped over plants and fixed to the ground.
By Ric Bessin, Extension Entomologist