Brown leaf spot of cassava

Brown leaf spot is a significant fungal disease affecting cassava plantations, caused by the pathogen Cercospora henningsii (also known as Passalora henningsii). It is recognized as one of the most common foliage diseases of cassava, occurring in almost all tropical and subtropical regions where the crop is grown.

The primary host for this fungus is cassava (Manihot esculenta). While it mainly affects the leaves, the disease can significantly impact the overall health of the plant by disrupting the photosynthetic capacity. Severe infections lead to reduced tuber weight, which is the primary economic component of the crop.

Symptoms initially appear as small, brown, circular-to-irregular spots on the leaf surface. As the disease advances, these spots enlarge and may develop a grayish or light-brown center surrounded by a distinct yellow halo. Under high infection pressure, numerous spots coalesce, leading to severe chlorosis and premature defoliation of the plant.

The development of the disease is highly dependent on environmental conditions, particularly high relative humidity and moderate to warm temperatures. Spores are primarily dispersed through wind, splashing rain, or movement of contaminated agricultural equipment. Dense canopy covers, which trap moisture, significantly favor the rapid spread of the fungus within the field.

To effectively manage brown leaf spot, an integrated pest management approach is essential. Key strategies include the use of resistant or tolerant cultivars, ensuring proper plant spacing to improve air circulation, and maintaining field hygiene by removing crop debris. In cases of severe outbreaks, the application of chemical fungicides may be necessary to protect the yield during critical growth stages.