What can I do to prevent tiny worms inside each cherry on my cherry trees?
There are two possible culprits for this condition: the western cherry fruit fly or the spotted wing drosophila. The females of both these insects lay their eggs in the cherries, and the small worms you are seeing are the larva. There is no effective remedy for the larva, so the control must be accomplished on the adult fly prior to the egg laying.
Treatments for the two are similar and require chemical sprays. Sprays should be applied only when the adults are present, and their presence should be determined by trapping. Trapping and spray recommendations from the Pacific Northwest Insect Management Handbook can be found at these links:
When using pesticides, follow the directions on the label and do not spray when blossoms are on the tree. For further assistance, please contact the Douglas County Master Gardeners at 541-672-4461.