By Lenny Wells
University of Georgia
Two problems particularly plague backyard pecan trees: pecan aphids and a disease called pecan scab.
Yellow pecan aphids rob nutrients and water from pecan leaves. They also produce a syrup-like solution called honeydew, which coats the leaves and drips down onto cars and houses, where an unsightly fungus called sooty mold develops. Large populations often cause trees to shed leaves in late summer, too.
Culprits get worse
The damage inflicted by black pecan aphids is much worse. These insects remove nutrients and water from the tree's leaves, too, but in doing so they release a toxin into the plant.This toxin causes the leaves to develop bright yellow spots, eventually killing that area of the leaf and turning it brown. When populations are heavy, black pecan aphids can defoliate a tree.
As bad as aphids are, though, the main reason backyard trees fail to produce pecans is pecan scab. This disease develops and spreads during rainy time, particularly when the nut is growing.
Nuts infected with pecan scab develop black spots on the shuck. Many will be covered so the entire nut turns black and falls before it's fully developed.
Ways to improve
Completely removing and destroying the leaves and shucks on which the disease overwinters can help reduce the carry-over of scab and other diseases. Removing low limbs can allow greater air flow, too, which helps to reduce the leaf wetness necessary for infection.In most cases, none of these problems can be controlled by spraying pesticides on large, backyard pecan trees.
Pecan varieties, however, do vary in their susceptibility to these problems, so take care to choose trees wisely.
Elliott is probably the ideal backyard pecan. It has the best scab resistance available and produces excellent quality nuts. Its small, teardrop-shaped nut fills easily. It often brings a premium price because of its plump, perfect halves.
The main problems with Elliott are that it may bear nuts only every other year and can suffer from black and yellow aphid problems. It is, however, relatively drought-tolerant for a pecan tree.
Sumner suffers less from scab than many varieties. However, it's highly susceptible to damage from black pecan aphids. Sumner has large nuts with well-developed kernels. It produces lots of pecans at a young age, and is a relatively consistent producer.
Stuart offers some level of scab control, too, although the nuts will scab under heavy disease pressure during wet weather. Many of the old yard trees in Georgia are Stuarts.
These trees usually don't suffer as much from black pecan aphids as some other varieties do. But they often harbor large populations of yellow aphids. Stuarts have large nuts with well-filled kernels that shell easily. And they produce fairly regularly.
Choosing the right variety for your yard may not eliminate problems with pecans. But it can certainly make problems less frequent.
To learn more about growing pecans and about many other agricultural topics, contact your county UGA Cooperative Extension agent.
(Lenny Wells is the University of Georgia Cooperative Extension state pecan horticulturist and a Dougherty County extension agent with the UGA College of Agricultural and Environmental Sciences.)
