Sour Cherry Trouble
I have a sour cherry tree in my yard that bears a TON of fruit. A few years ago, all the cherries had tiny worms in them. A local nursery told me it was a specific fly that lived in the lawn and laid eggs when the fruit started to mature. So we spayed as instructed and had two good years with no problems. However, the last two years, the fruit is sort of rotting from the inside out, just before it ripens. It seems similar to the prior infestation, but there is nothing living inside, just brownish. Seems this year's harvest is lost, but I really would love to know how to prevent it next year. Anyone have an idea?
I would say to go in with the Sevin insecticide all over the lawn a few times a year, and the tree right as the fruit is maturing. But make sure to follow the treatment/harvest guidelines on the container. The fly larvae won't survive. Beyond that, figure out the best soil amendments and conditions for the tree and your area so the fruit is as best as it can be!
Sevin is kind of nasty but where tree fruit is concerned sometimes you gotta do what you gotta do. We use dormant oil followed in two weeks with a copper sulfate spray and again with copper sulfate right before the buds open.
If you still have some of the fruit take it to your local cooperative extension agent or a local nurseryman for identification of just what you've got. It may not be a bug, it could be a disease or blight of some kind.