In addition to the shade and delicious nuts you receive from your pecan trees (Carya illinoensis), these deciduous plants also display green foliage that turns to a brilliant yellow hue during autumn. Unfortunately, the beauty of the pecan tree can swiftly fade when insects called pecan phylloxera cause unsightly galls, or swollen tissue, to appear on leaves. While there is no cure for these bumps, consider natural preventive care to keep your trees healthy.
Because the bumps cannot be removed or cured once they develop, providing consistent care to your pecan tree is the most effective way to manage this problem. Begin by growing your trees in areas of the landscape that provide full sun to partial shade. For best growth, maintain moist, well-drained soil high in organic content; pecan trees will thrive in either acidic or alkaline conditions and will tolerate periods of flooding. Pecan trees perform most successfully in U.S. Department of Agriculture plant hardiness zones 5b through 9a.
A small insect that resembles a wasp, known as the pecan phylloxera (Phylloxera devastatrix), is responsible for galls on your pecan trees. Similar to aphids, these tiny, yellow-brown to cream insects measure 3/32 inch in length. Eggs overwinter on pecan trees, typically hatching during the spring. The hatched phylloxera feed on new plant growth, such as leaves and buds, where their feeding causes a tree reaction resulting in the growth of plant tissue over the feeding insects.
The phylloxera insects mature within galls and then emerge, leaving cosmetically damaged leaves. General feeding may also cause the development of galls on nuts and stems. While damage is often only cosmetic, severe infestations may lead to malformed leaves as well as dry foliage. Leaves often drop early from the tree. Pecan trees may also experience twig dieback and overall diminished health. Galls occur once annually, though trees are unlikely to be infested several years in a row.
While chemical and botanic-based insecticides are available for home use, they are not recommended. Once galls have formed, they cannot be cured or removed, and applying insecticides is neither cost effective nor helpful. Because you will likely not see a subsequent infestation the following year, you should give your tree the time to heal itself. Maintain excellent care of your trees so they can recover from pests. Fertilize your trees once annually with four pounds of 10-10-10 fertilizer per inch of trunk diameter, suggests the North Carolina State University Cooperative Extension.