I am trying to grow raspberries in Carlton County. This year my berries came on very nicely but I have some type of teensy white worm in the berry itself that turns the berry mushy. I can't see the worm until I pick the berry and look inside. I always know which berry will be infected because the tip of it will be squishy even though the berry is not overly ripe. In my earlier crop, almost all the berries were infected. Recently I am picking from my fall-bearing Heritage raspberries and am finding a few worms, not as many as in July. The farm is organic so I can't spray. Can you tell me what this worm is and are there any suitable treatments for it?
Carlton County Minnesota
Thank you for the question. How disappointing to find these larvae on your raspberries! From your description of the larvae, you may have spotted wing drosophila [SWD] larvae. SWD are fruit flies that cut a slit in the fruit and lay their eggs. When the eggs hatch the larvae which are white and about 1/8 inch long eat the fruit from the inside. I don't know if SWD has been found in Carlton County or not. If you think this is the pest you have, it is reportable to the Minnesota Department of Agriculture at this site: Arrest-the-Pest program.
Please read these two publications on management recommendations for SWD. There is advice for organic growers as well.
Thank you for contacting Extension.