Brown leaf spot of pecan

The causal agent of brown leaf spot in pecan is the fungus Mycosphaerella caryigena (anamorph Cercospora fusca). This ascomycete fungus is a significant pathogen that affects pecan orchards, specifically targeting the foliage and causing severe physiological stress to the trees.

The host range is essentially limited to the pecan tree (Carya illinoinensis). The disease attacks leaves, inhibiting the plant's ability to photosynthesize effectively, which is critical for nut filling and the accumulation of carbohydrates necessary for the tree's health during the dormancy period.

Symptoms appear as brown to reddish-brown circular spots on the leaf surface. As the infection progresses, these lesions expand and darken, frequently leading to chlorosis of the surrounding tissue. In severe cases, the tree experiences premature defoliation, which can occur well before the natural autumn senescence.

The pathogen thrives under conditions of high humidity, frequent rain, and moderate temperatures. It survives the winter primarily in fallen leaves on the orchard floor. When spring arrives, spores (ascospores) are released into the air or splashed by rain onto newly emerging foliage, initiating the seasonal disease cycle.

Management of brown leaf spot relies on an integrated approach. Sanitation is the first line of defense; raking and destroying or tilling under the leaf litter reduces the initial inoculum. Additionally, a regular fungicide spray program, scheduled according to weather conditions and disease scouting, is essential to minimize losses and maintain canopy health until the end of the season.