Some of the pecans on our trees are turning black and falling off the tree. When cut open, the insides are black and not mature. What causes this and what is the solution? Some of the other pecans are starting to get black spots on them. There have been very few webworm nests this year and we have cut most of the nests out of the trees. The trees are about 35 years old and seem healthy. This problem has been getting worse in the last 3 or 4 years.