Fruit flies!

Asked August 21, 2019, 11:57 AM EDT

Hello! We have a sour cherry tree and raspberry bushes that all were affected by the terrible fruit fly! I noticed a few larvae last year in my cherry tree, and many more this year! I’ve read that they’ll just get worse and worse if not dealt with properly. What’s the best course of action to eliminate them? Thanks again! Lauren

Hennepin County Minnesota

3 Responses

Thanks for the question.

The white worms inhabiting your raspberries and cherries are larvae of the Spotted wing Drosophila (SWD). These larvae emerged from eggs laid in the developing berries and fruit during this past June by adult SWD.

Most people discard any berries or fruit in which these larvae are found.

Unfortunately once raspberries are infected, there is very little that can be done. The berries are already destroyed. As you suggested in your question, your focus should be aimed at preventing a reoccurrence of this in 2020. Here are some sites that will help you in these endeavors (note that in these sites some “natural” ways to combat this pest are described – good clean up this fall and the use of netting next spring):

https://extension.umn.edu/yard-and-garden-insects/spotted-wing-drosophila

https://blog-yard-garden-news.extension.umn.edu/2019/07/spotted-wing-drosophila-update-and.html

https://blog-fruit-vegetable-ipm.extension.umn.edu/2019/04/author-matthew-gullickson.html

https://blog-yard-garden-news.extension.umn.edu/2018/06/spotted-wing-drosophila-is-active-now.html

While the netting approach does take some work, it is currently the most commonly recommended preventative measure. It will be critical that this netting be installed before berries start to develop. At one time there was concern that this netting would prevent the entry of insect pollinators. This has turned out to be a very minor problem as raspberries are typically wind pollinated.

With respect to the cherry trees, netting is probably not feasible. Insecticidal spraying is one possibility. However this would have an adverse effect upon the desirable pollinators that you need to do the pollination for fruit development. The following suggest other alternatives;

http://treefruit.wsu.edu/crop-protection/opm/spotted-wing-drosophila/

https://extension.psu.edu/tree-fruit-insect-pest-spotted-wing-drosophila

The following publication discusses various traps that you could make to hang around your trees:

https://extension.oregonstate.edu/pests-weeds-diseases/insects/spotted-wing-drosophila-swd

Good Luck!!

Thank you! This is all very helpful and I appreciate you taking the time to answer my question. Take care!

You're entirely welcome. Good Luck!