We have identified our first spotted wing drosophila (SWD) of 2014 in western Kentucky. It was present in a trap maintained by Patty Lucas in the Purchase Area of the state. The timing of this capture is very close to the date of our first report last year. A trap had one female on June 12, and those same traps had 5 females the following week (Figure 1). Based on our experience in 2013, SWD captures are likely to spread across the Commonwealth over the next 2 to 4 weeks and intensify as the season progresses.
Producers of susceptible crops (raspberries, blackberries, blueberries, and grapes) that still have crops in the field should put out spotted wing drosophila traps, if they haven’t already done so.
Traps and Bait
We use 1-quart deli containers with a pair of 1 ½ -inch by 3-inch windows cut in the sides. We hot-glue ¼-inch plastic screen over these windows to keep out larger flies (Figure 2). The bait is a mixture of baker’s yeast, sugar, water, and dishwashing soap. To make enough bait for two traps, mix ½ tablespoon yeast with 1 tablespoon sugar, 1 cup water, and one drop of dishwashing soap. Check the traps weekly, pour the contents into another container for identification, and refill the traps with fresh bait. To clean the samples, pour the contents through a reusable coffee filter and rinsing with water to clear out the yeast.
Interpreting Trap Findings
If you don’t find SWD, you do not need to spray insecticides during the harvest period. If you do find SWD, then you need to begin a concerted SWD management program. It may mean spraying during the harvest period, so producers need to carefully observe all pesticide label instructions including Pre-Harvest Intervals. Sprays for SWD need to provide excellent coverage, so pressure and spray volume need to be sufficient for coverage throughout the canopy. Reapply sprays on a weekly basis, as well as after a significant rain. Check Entfact 230 (listed in the resources, below) for a list of SWD recommended insecticides and their respective pre-harvest intervals.
Other Management Tactics
It is important to use other SWD management tactics besides only relying on sprays.
Producers not wanting to use insecticides may use fine mesh netting. The netting needs to have a mesh size fine enough to prevent SWD females from passing through, so pore sizes of less than 0.98 mm are needed. The netting needs to be sealed around the base and in place before fruit begin to ripen.
Clean harvest is also a key management tool. For clean harvest, pickers use two containers when picking, one for marketable fruit and the other for all other ripe fruit. Removing the unmarketable fruit from the field reduces the buildup of SWD. Unmarketable fruit should be placed in clear bags, sealed, and left in the sun. Burying SWD-infested fruit is ineffective as this insect has been shown to emerge from the soil.
Post-harvest care of berries is another important management tool. As soon as berries have been harvested, they need to be refrigerated. This suspends the development of SWD by delaying egg hatch, growth, and feeding by larvae (Figure 3). Temperatures as close to but above freezing are best. Freezing berries will kill all immature stages.
See our factsheets for a description of biology, identification, and SWD management:
- Spotted Wing Drosophila, Biology, Identification and Monitoring http://www2.ca.uky.edu/entomology/entfacts/entfactpdf/ef229.pdf
- Spotted Wing Drosophila Management (discusses trapping, identification, and management) http://www2.ca.uky.edu/entomology/entfacts/ef230.asp
- Spotted Wing Drosophila and Backyard Small Fruit Production http://www2.ca.uky.edu/entomology/entfacts/entfactpdf/ef231.pdf
By Ric Bessin, Extension Entomologist