Plums and apples fall from tree before they are ripe.
Out of 8 apples trees, one apple tree has dropped its fruit before they are ripe every year. All apples fall off green, hard, and unpalatable. Unknown type of apple.
All 7 of my plum trees drop their fruit before they are ripe. Perhaps 5 on one tree will ripening properly. A small portion of them get damaged and half of those ripen or rot on the limb. The rest fall off green and hard. Occasionally, a few will ripen on the ground, if animals do not eat them. This has gone on for the lifetimes of the trees. Unknown type of plum; fruits are about 1-1.5 inches in diameter and deep pink to deep red when ripe.
What causes this and how does one prevent it?