Plant Diseases/Plum trees
For the last two years, I have had two plum trees that after fruit starts growing,they turn color like they are ripening long before their time. They are small and just fall off the tree. Some even fall off before they turn color. They don't ripen, as they are still hard and small. By late June when they should be ready for harvest, they have all fallen off. The tree-leaves and bark-appears healthy. I don't know the variety of plum,but the fruit is normally about 1 1/4 inch in diameter. What could be causing this?
Your fruit issue does not sound like an infectious type disease and probably not an insect. Sometimes an environmental extreme like sudden temperature fluctuations (especially high temps can interfere with pollination)may cause this. As a caution, consider examining the affected fruit for small holes. This could be a small insect- however as mentioned it doesn't sound like one.
Also, consider have a soil test done to be sure that the tree is getting everything it needs from a nutrition standpoint. Be sure to also maintain good soil moisture be supplemental watering as needed.