Nearly ripe peaches have been falling off my peach tree rapidly. Nearly all of them look normal. However, when opened there is a black moldy, pulp type substance all around the pit. There is also an odd semi sticky black substance laying in the top portion of the split of the peach. It's also black in appearance. What is this?
The black mold sounds like sooty mold fungus, which is often caused by insect pests. Neem oil will help with both issues (the pests and fungus). For additional reasons for premature fruit drop, this article will help: https://www.gardeningknowhow.com/edible/fruits/peach/peach-tree-fruit-drop.htm