I have 2 sour cherry trees in Duluth that are between 15 and 20 years old. Last year they produced an incredible abundance of cherries. This year there is something wrong with them: Some leaves have fallen off, and the cherry quality is terrible. Many of the cherries are black or brown inside, and they seem to go straight from under-ripe to rotten. At first I thought the trees are just getting too old (I know they're short-lived). But now I think they have an insect or disease infestation. The last time I picked some, I had the container in the fridge and opened it the next day to find many tiny white pieces on top, like miniscule grains of rice. What do you think is wrong and what can I do about it? Thanks much.