Pecan Scab is the most economically significant disease of pecan trees (Carya illinoinensis) in the southeastern United States. Fusicladium effusum is a fungal plant pathogen that causes pecan scab. Fusicladium effusum causes lesions and tissue death on pecan twigs, petioles, leaves, nuts and shucks beginning in early spring, with multiple cycles of infection repeating until late summer. Wind and rain spread the fungus to a susceptible host. Control of the disease is achieved by fungicide, sanitation and, in some cases, quarantine.