According to the University of Missouri Extension, pecan trees account for 12,000 acres of commercial growing land in Missouri alone. However, even if you only have one pecan tree you probably are devoted to its health not only for the harvest that it yields, but for its aesthetic appeal as well. Pecan diseases can diminish the yield of a pecan tree and even kill it. Nearly always the first signs of problems start in the leaves, so keeping an eye on pecan foliage is the best way to spot problems early and prevent them from spiraling out of control.
Pecan scab is a fungus that lives on the leaves of pecan trees. It creates small, circular, dark spots on the bottoms of the leaves that enlarge, coalesce and even rot away, leaving holes in the pecan leaves. Left untreated, the scab can infect the nuts, causing premature drop and sticktights, nuts that are hard to shell. You can prevent scab infections by pruning the tree's canopy to allow light into the center of the tree and improve air circulation. Once the tree develops scab, you may be able to treat it with fungicides, but often the tree will have to be removed to prevent the spread of infection.
Leaf Spot Disease
Leaf spot disease starts out as small, dark spots on the leaves. If you do not treat it, then the spots will increase in diameter and develop yellow rims around the edges. As spores develop they will form white, fuzzy spots in the centers of the spots. Eventually the infection can cause the leaves to yellow and drop. Use sterile pruning to remove and dispose of all infected leaves. Fertilize the tree to help keep it healthy and help it recover from the infection. If necessary, you can spray with a fungicide but check with a local professional since not all sprays are legal in all areas.
Powdery mildew affects the leaves and nuts of the pecan tree. It looks like chalk dust and is black, gray, white or pink. Powdery mildew is usually a cosmetic problem, but when it attacks the nuts on the tree is can make them inedible. Control powdery mildew by cutting off affected leaves and branches using sterile pruning. Do not drop the plant material on the ground, or the infection will just return to the tree. In most cases this will resolve the issue, but if not, you can treat the tree with a fungicide.