Our 1/2 acres school garden has an old cherry tree (not sure of the variety, they start out looking like Rainier but darken as they ripen to a deep red-purple, Bing looking fruit) and raspberry bushes planted next to it. In the past two years our cherry crop has been totally ruined by an infestation of fly larva, that I now believe to be Spotted Wing Drosophila (SWD). This year, the infestation has spread to the adjacent raspberries and I fear the grapes are next. What can I do to mitigate this problem? Are there traps available from OSU extension? Should the raspberries be cut to the ground? How can the spread of infestation be stopped? Please help. Thanks -Nicolas Townsend
It’s possible that SWD (spotted wing Drosophila) have infested the cherries but we must also consider Western cherry fruit flies which have been troublesome here in the northwest for many more years than SWD. The best way to determine which fly is present is to rear the larvae (youngsters) to adult stage.
You can easily do so at home, on the counter, in a closed, clear container with a vented lid, perhaps paper toweling secured with a rubber band; add several infested cherries, add the lid and, then, wait for a week or more until you have flies.
If the fly is SWD, it will look very similar to small nuisance fruit flies; if it is the cherry fruit fly, it will be nearly the size of a house fly, but with wings heavily marked with black. (See http://cru.cahe.wsu.edu/CEPublications/FS125E/FS125E.pdf)
When it comes to SWD, raspberries are one of its favored hosts but not grapes. (Apparently, the thicker skins of grapes offer some protection against egg-laying.)
If you have additional questions after you read these publications, please ask:
- Recognize Fruit Damage from Spotted Wing Drosophila: https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/em9021.pdf
- Protecting garden fruits from spotted wing drosophila: http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/20883/em9026.pdf