How Should Growers Manage Spotted Wing Drosophila in Rainy Conditions?

— Written By Hannah Burrack
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The last two days have been particularly rainy in the southeast, and if the forecast is right, our rainy weather will continue all week. Rainy conditions complicate already challenging spotted wing drosophila (SWD) management because we have little information on the rainfastness of the insecticides available for use against this pest.

I recommend that growers make weekly treatments of recommended insecticides to prevent SWD infestation in ripening and ripe fruit and that they reapply SWD treatments following a rain event.

What is a grower to do, however, in a week like this when rain is forecast nearly every day? I suggest that growers wait until there will be a least a day without rain to reapply materials. It does little good to treat today and then have the material washed off tonight. In this type of weather, our ability to manage SWD with insecticides is greatly reduced, and growers should increase their focus on keeping fields clean to minimize the risk of larvae developing in unpicked fruit.

Unpicked ripe fruit, damged fruit, or overripe fruit may harbor SWD populations and should be removed from the field and destroyed. As I discuss here, some of the best ways to dispose fruit is to either bag it and haul it offsite or to bag it in sealed, clear bag and “bake” it in the sun for a few days to kill any larvae present. Burying fruit does not necessarily kill larvae, nor does piling fruit near fields or dropping them in the row middles.

One somewhat bright spot, while we don’t have good rainfastness data for most of the materials recommeded against SWD, our research plots at the Central Crops Research Station, Clayton, NC, were rained on much more last year than this year, and two of the materials we used, Brigade and Radiant, did performed better than other materials tested, even under these rainy conditions. This suggests that they have some degree of residual activity even when it’s rainy.

In summary: I recommend retreating, but not if it’s going to rain right after and when they cannot treat, growers should redouble their efforts to keep their fields clean.

More information

SWD posts – Strawberry Growers Information

Fruit recommendations – NC Agricultural Chemicals Manual

What should growers and homeowners who find SWD do?NC Small Fruit & Speciality Crop IPM

Written By

Hannah Burrack, N.C. Cooperative ExtensionDr. Hannah BurrackProfessor & Extension Specialist and Director of Education & Outreach, NC PSI Call Dr. Hannah Email Dr. Hannah Entomology & Plant Pathology
NC State Extension, NC State University
Updated on May 20, 2013
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