Cercospora leaf spot of pecan

The fungus Cercospora fusca is the primary causal agent of a specific leaf spot disease in pecan trees. This pathogen is known to colonize the foliage, leading to physiological stress and premature shedding of leaves, which negatively impacts the overall tree vigor.

The primary host for this fungus is the pecan tree (Carya illinoinensis). While it is highly host-specific, the infection can spread rapidly across an orchard if environmental conditions favor the development and dispersal of fungal spores.

Initial symptoms are characterized by the appearance of dark, brown-to-black spots on the leaves. As the infection progresses, these lesions often coalesce, covering significant portions of the leaf surface. Affected leaves typically develop chlorosis and drop prematurely, starting from the lower canopy.

The fungus thrives in environments with high humidity, rainfall, and moderate temperatures. The pathogen survives the winter in fallen leaves and debris, producing new spores in the spring that serve as the primary source of inoculum for the new growth season.

The economic impact of the disease is significant, as reduced photosynthetic area limits the tree's ability to fill nuts properly, resulting in lower yields and smaller nut sizes. Management strategies rely on cultural practices, such as removing leaf litter, combined with timely applications of fungicides when disease pressure is high.