Pecan trees are grown both for their landscape value as shade trees and commercially for their nuts. They are attractive to more than 20 types of insects but only a few actually cause harm, primarily to the nuts rather than the trees. Disease and weather can also play a role in damaging pecan trees. There are signs to watch for that will allow you to either prevent some forms of damage or deal with damage after it occurs.
Pecan trees need well-drained soil with good water retention capabilities. Soil must be loose, not compacted and pecan trees should be planted where they receive full sun. Without the proper soil and sun conditions, pecan trees will become stressed. Stressed trees of any kind are more inviting to insects and easily infected by disease. Insects and disease can cause damage, sometime irreversible, to pecan trees.
Wind, Rain or Snow Damage
The most common weather damage on pecan trees is from storms and ice or snow. Severe winds can damage limbs and even uproot trees. Heavy snow or ice can crack limbs leaving trees lopsided and possibly subject to uprooting. Heavy rains and fierce winds can defoliate a tree reducing the tree's ability to make sufficient food for itself. Rain and wind can also cause fruits to drop prematurely reducing the harvest. Severe damage can have an impact on the production levels in subsequent years.
Aside from cracked limbs in the winter, pecan trees can suffer damage just by freezing. Signs of freeze damage include vertical splits in the bark and wood that appears dried out and gray in color. In the spring, some limbs appear dead and the tree sends up new growth from the ground. Sometimes the south or southwest side of the trunk dies and the tree sends up new shoots on that side. Another sign can be the sudden death of a limb that sprouts new growth that in turn dies as well.
The Asian ambrosia beetle makes holes into trees to lay eggs. They leave behind a small protrusion that resembles a toothpick extending outward from the trunk and sometimes from the main scaffold branches; then they lay eggs in the cambium. When the larvae hatch, they feed on the cambium leaving galleries under the bark. Leaves will wilt at the site of the infestation and the tree will become girdled and die.
Spider mites feed on the sap on the underside of leaves. They leave brown spots in their wake, making the leaves look scorched. The black pecan aphid can cause severe leaf damage. During their feeding process, they inject a toxin into the leaf that results in a brown dead spot 1/4 inch across. Stink bugs feed on the sap in nuts. If the shell has hardened before the feeding begins, the nut will have darkened spots that taste bitter. If the shell has not hardened when feeding begins, the nut will fall prematurely. Pecan weevils feed on the nuts. If the feeding occurs during the water stage, the nut will drop. During the gel stage, the weevil lays eggs in the nut and the larva will feed on the nut meat inside the shell.
Some diseases can cause damage such as pecan scab that leaves black spots on the leaves and shucks. Cotton root rot is a serious disease because it normally progresses very rapidly. A sudden wilting of the entire tree in late summer is the only indication just before the tree dies. It is a soil-borne fungus and there is no cure for it.
Shuck dieback damages the nuts. Shucks are black and the nuts are only half-filled when they prematurely fall from the trees, usually in August.