By Clint Thompson
In his UGA Extension blog, Brett Blaauw, Assistant Professor in the University of Georgia Department of Entomology, alerted grape farmers that management for spotted wing drosophila (SWD) is approaching soon.
SWD flies are active year-round but near veraison, as the brix levels in wine grapes reach 15 degrees Brix, the grapes become attractive and susceptible to SWD. SWD and other drosophila flies can spread and exacerbate sour rot.
Management is key. Proper sanitation of the vineyard can reduce populations. If farmers harvest grapes frequently and remove fallen or unmarketable fruit, it will prevent the buildup of ripe or rotting fruit. This reduces sour rot inoculum and potential breeding areas for the flies.
Insecticides are effective at killing adult flies and are recommended if you have a history of SWD in your vineyard or have prior issues with sour rot. Insecticide treatments should begin when grapes are near 15 degrees brix. Treatments should be applied at least every seven to 10 days. Rotating insecticides with different modes of action is very important.
Make sure to read the label and check the pre-harvest intervals before applying any chemical.
Note that the combination of an insecticide and Oxidate 2.0 significantly reduced SWD and sour rot prevalence in treated plots.
If you are unsure whether SWD is a problem at your vineyard, it is easy to monitor for the flies. Traps can be made from plastic cups with lids.
As always, management recommendations can be found at:Â https://smallfruits.org/files/2019/06/BunchGrapeSprayGuide.pdf.