Why does my prune plum tree drop its fruits early?
There are several reasons that cause early fruit drop. There are pests and diseases that can cause the fruit to drop, the main one seems to be the Plum Curculio. The Curculio leaves a mark on the fruit which may be visible to you on the fruit, but also is visible on the foliage earlier in the season. There is more information on this pest (and on diseases) on line and from your County Agent. Another cause of fruit drop is natural thinning by the tree. Sometimes the tree production is too much for the tree to support, so it drops the excess. If you do not have enough rain, the fruit will drop. Also, if there is insufficient pollination of the fruit, the fruit will drop--this may be due to too few bees or bad weather during pollination time. I hope one of these suggestions will be helpful to you.
For more information on the snout beetle plum curculio (Conotrachelus nenuphar) and its control, see
Cornell University's Plum Curculio Fact Sheet