The fungus overwinters in fallen leaves. Fungicides applied for scab control are also effective against Gnomonia leaf spot. The first sign of the disease appears in May and June. Circular, dark brown spots appear along the midrib on the lower surface of the leaves. In late summer the spots turn a cinnamon brown or liver color.
Liver spot can cause severe defoliation, particularly during prolonged periods of wet weather.
Weak trees are more susceptible to liver spot than are healthy trees. The best control for liver spot is keeping trees healthy by watering and fertilizing them when needed. This disease can also be controlled by fungicide sprays used for scab. Leaf spots on the upper surface of pecan leaves are grayish brown, with concentric ring formations that are more distinct on the lower side of the leaf. Leaf spots on the lower surface are light brown in the center, becoming darker brown toward the edge.