Pecan brown leaf spot

Brown leaf spot, caused by the fungus Passalora effusa (syn. Cercospora effusa), is a significant foliage disease affecting pecan trees. It is one of the most common diseases in humid pecan-growing regions, causing premature defoliation that can severely impact the quality and quantity of the nut harvest.

The primary host for Passalora effusa is the pecan tree (Carya illinoinensis). The pathogen thrives in environments with extended periods of moisture, such as frequent rainfall, heavy dews, or high humidity levels. Orchards with poor airflow or those lacking proper sanitation are particularly susceptible to severe outbreaks of the disease.

Symptoms typically manifest as small, irregular, olive-gray to brown spots on the underside of the leaves, where the fungal spores (conidia) are produced. On the upper surface, these spots appear as chlorotic or necrotic lesions. As the infection progresses, these spots coalesce, leading to extensive tissue death and subsequent leaf yellowing and dropping.

The development of the fungus is highly correlated with weather patterns. The primary infection cycle begins in the spring from spores overwintering on fallen leaves and debris. Throughout the growing season, secondary infections occur rapidly as airborne spores spread through the canopy, especially when leaf wetness duration is prolonged.

Management of brown leaf spot requires an integrated approach to maintain tree vigor and reduce inoculum pressure. Key strategies include:

• Sanitation: Removing and destroying leaf litter to reduce overwintering spores.
• Pruning: Enhancing canopy airflow to reduce leaf wetness duration.
• Fungicide Application: Using recommended fungicides during the spring and early summer when environmental conditions are favorable for fungal spread.
• Monitoring: Scouting the orchard for early symptoms to time control measures appropriately.