Pecan scab is a common fungal disease of pecans. Symptoms include black lesions and tissue death on twigs, leaves, and nuts from early spring until late summer (Fig. 3).
Wind and rain spread spores of the disease organism. Because rain and high humidity increase scab infection, pecan scab is more severe in Central and East Texas.
Control: Planting pecan varieties with resistance to pecan scab can reduce disease incidence in Central and East Texas. Other actions to minimize pecan scab are proper pruning and wide spacing between the trees, which can improve air circulation and speed leaf drying.
Fungicides applied as a foliar spray on young trees can prevent pecan scab. To maintain control, they must be applied early and then reapplied. The fungicides labeled for control of pecan scab on bearing trees are not available in small quantities marketed for backyard trees.
Several other diseases can infest pecans, including bacterial leaf scorch, downy spot, powdery mildew, shuck dieback, and stem-end blight. Soil-borne diseases include cotton root rot, crown gall, and root-knot nematodes.
These diseases are often difficult to diagnose and control. For assistance, contact your local office of the Texas A&M AgriLife Extension Service or a certified arborist. Diseased plants can be submitted for disease identification to the Texas A&M Plant Disease Diagnostic Lab at https://plantclinic.tamu.edu/.