Spotted Wing Drosophila Active Early This Year

Last week on May 1, we captured our first spotted wing drosophila (SWD) detected in Fayette County. This was a single male and its occurrence is quite a bit earlier than previous years. Over the 5 years of trapping this invasive pest, the first capture has been earlier each year.  There are a number of possible reasons for this, including SWD is becoming active earlier each year, traps are becoming more effective so that we can capture them when SWD are at lower numbers, a mild winter increased SWD numbers making them easier to detect, or that Kentucky experienced an early spring. We don’t know.

Figure 1. Male spotted wing drosophila (SWD) captured May 19, 2016 in Caldwell County (Photo: Ric Bessin)

So now that we have captured the first SWD, what does this mean? For that particular field using an insecticide weekly to control SWD is warranted through the remainder of harvest. This does NOT mean that other fields throughout Kentucky need to be sprayed. It stresses the need for producers to monitor for this pest in their own fields. Trapping needs to begin no later than 10 days before the first harvest or when the first fruit begin to turn color and soften. If no SWD are detected, then sprays for SWD are not justified.

Figure 2. Strawberries are potentially at risk of infestation with this early spotted wing drosophila capture (Photo: Ric Bessin, UK).

This first capture of 2017 has occurred during the strawberry harvest period, but we have not received any reports of SWD in strawberries. This was also just one male fly; the following trapping period was free of SWD. Commercial strawberry producers are advised to use the floatation method weekly with undamaged berries to monitor for fruit infestations. This method is listed in the second factsheet referenced below.

In some regions of the country, producers must meet zero tolerance requirements for insect infestation of the fruit when shipping blueberries, blackberries, or raspberries for wholesale marketing. Many of these producers do not have enough confidence to wait and spray for SWD based on detection in traps and instead spray preventively to meet these strict requirements. Many of the Kentucky small fruit producers market crops locally and can tolerate a very low level of infestation by working directly with consumers. Trapping and spraying as needed has worked well in Kentucky and has been the most economical for our growers.

Additional Resources

For a list of recommended insecticides for SWD on various crops, see:

Spotted Wing Drosophila Management (Entfact 230)

For a list of cultural and physicals controls for SWD, see:

Spotted Wing Drosophila and Backyard Small Fruit Production (Entfact 231)


By Ric Bessin, Extension Entomologist


Posted in Fruit