A common disease afflicting pecan trees is scab. Brown spot, downey spot, gnomonia leaf spot, liver spot and zonate leaf spot are several fungal diseases that pose a threat to the leaves on pecan trees.
Scab is a fungus that looks like small, round spots that are green or black. Scab lesions are likely to attack the tissue of young pecan trees in the growing stage. Scab can stunt the growth of pecan nuts or cause deformities.
Brown spot primarily shows up on mature leaves of neglected trees in June or July. If not prevented, it defoliates trees by October. Downey spot is a problem for susceptible tree varieties such as Pawnee, moneymaker and Stuart. It damages nut production. Gnomonia primarily endangers trees lacking in nourishment and zinc. The first signs appear in June. Liver spot also attacks weak trees. The dark brown spots can cause severe defoliation. Zonate leaf spot disease favors moist conditions. It starts out as grayish brown rings, later evolving into a crystalline-like fungus.
Powdery mildew is a fungus that grows on leaves and nuts. It is recognized by its powder-like appearance. This disease does the most damage to young nuts. Mature nuts survive with little to no damage. Crown gall is a disease that causes plant tumors, which interferes with nutrient and water absorption.