Everything is going along fine, then your favorite tree’s leaves begin to drop. What caused this and will the tree die? Here is a list of factors that could lead to mid-summer leaf drop.
1. In droughts, a tree may shed up to 10 percent of its leaves. This helps, because then it loses less water into the air. Loss of this much food-making capacity does little harm.
2. Vigorous trees may produce too many leaves. In wet springs, foliar growth may be over lush. Once normal summer dryness arrives, the excess leaves drop in adjustment. Such physiological leaf drop doesn’t hurt trees.
3. Inner leaves and twigs are “shaded out” by the upper outer leaves. They die for lack of sunlight and drop off, leaving the large, low branches bare near the trunk. This is normal, not harmful.
4. Individual leaves may fall when shaded out by dense crust of dark fungi called “sooty molds.” These grow in sugary excretions of aphids called “honeydew.” If you kill the aphids, the dark molds go away and vanish.
5. Leaves may form a normal “abscission layer” at the bases of their petioles (as though it were fall) when tricked by imitations of plant hormones produced by certain leaf spotting fungi. An example of a disease causing leaf drop would be apple scab on crabapple trees. Not all leaf spot diseases cause this. Severe cases may weaken the tree, so the next spring’s foliage should be protected with a fungicide. Leaf spots are most abundant after rainy springs.
6. Chemical injuries may cause leaf drop. Effects depend on the chemical, season, temperature, tree species, ect. Some chemicals discolor or disfigure leaves, but the leaves do not fall. Some cause leaf drop that may or may not harm the tree, depending on the severity. Other misapplied chemicals can kill an entire tree.
7. Fallen leaf clusters, attached to short twigs, may result from a twig-girdling in- sect. A shallow depression encircles the broken end of these twigs.
8. When squirrels gnaw off sprigs, the break is diagonal and may have two or three small bites. Hundreds of such sprigs may litter the ground under a single tree, but even then, there is rarely any threat to the life of the tree. This is somewhat common in this part of North Carolina. It is common in early spring and again in the fall. Squirrels will strip large patches of bark from branches, effectively girdling that segment of the plant.
9. The violent wind and thunder storms of summer can also cause twig and leaf fall. Again the quantity of lost leaves is not sufficient to harm the tree.