Black Spots on My Pecans and Leaves

Pecan Scab

• Pecan scab of the fungus Cladosporium caryigenum is a disease that causes black spots on both the leaves and nuts of the pecan tree. It initially attacks the leaves in the spring and gradually moves into the shucks of the nut throughout the summer. In severe cases, the entire tree may defoliate and infection of the nut results in reduced quality -- including loss of size -- and the potential abortion of the nut from the pecan tree.

Infection Process

• Pecan scab infection is the result of spores released by fungus lesions that have overwintered in fallen leaves, nuts or shucks. The disease is more likely to be significant and spread more easily when the spring is particularly wet or large amounts of dew dot the leaves of the tree. Pecan scab initiates as tiny, circular, olive-green or black spots on the leaves of the tree and husks of the nut.

Damage

• The black spots on the leaves continue to increase, eventually leading to a dropping of the leaves. Similarly, the black spots on the nut husks increase and grow together, leading to a husk that may be entirely blackened. Noting the injury, other fungi often attach to the nuts, causing additional damage. One condition -- known as "stick tight" -- occurs when the infection causes the nut to refuse to separate from its shell.

Prevention/Solution

• The best management technique is to consult a county extension agent as to the most resistant varieties of pecan tree to plant for a specific areas. Commercial growers regularly apply fungicides to battle pecan scab, but this is typically not feasible for home growers due to the special equipment needed to properly coat a large tree. The best option for home growers is to prevent infection by removing and destroying all infected leaves, shucks and nuts every fall.