Scout for Spotted Wing Drosophila in Small Fruit

David Owens, Extension Entomologist, owensd@udel.edu

Blueberry picking has begun, and the first blackberries and black raspberries are ripening up nicely. What this means is that if you haven’t already, now is the time to be scouting for spotted wing drosophila. This fly is the only one that will infest ripening fruit as soon as they start coloring up. They have very short generation times, about a week to 10 days. Populations are only going to build during the summer through the Fall primocane bearing season. This also means that insecticide mode of action rotation is extremely important to prevent resistance from developing. Male flies have a characteristic spot on the edge of the wing, but females do not. Females have a serrated ovipositor but you need high magnification to see it.

You can monitor for SWD using apple cider vinegar and putting in a small ball of fermenting wheat dough placed in a deli cup with ¼ inch holes drilled in the side. Alternatively, a tablespoon of active dry yeast, 4 tablespoons of sugar in 12 oz of water can be used, per Michigan State guidance. While you can wait as long as a week to check traps and replace the cider vinegar, the traps will fill up with other insects and other relatively unimportant native drosophila flies. If traps are checked more frequently, it will help with the sorting.

Scouting a planting can be done by gently squeezing fruit and looking for ‘leaky’ fruit. Infested blueberries will leak out fluid from oviposition holes. Raspberries tend to melt down onto the foliage. You can also do a salt water float to inspect for live larvae. There is a very good video on how do this here: https://www.youtube.com/watch?v=jsdcDsJOgoM. Insecticide options include the diamide Exirel, pyrethroids, organophosphates (Malathion) and spinosyn insecticides (Entrust and Radiant). Pay attention to application rate and frequency restrictions, along with pre harvest intervals. Increasing your harvest frequency and removal and destruction of bad fruit will help reduce SWD impacts. Also be sure to scout for secondary pests. Pyrethroids and Malathion are broad spectrum insecticides that will remove beneficials.

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