Exserohilum

Exserohilum is a genus of dematiaceous filamentous fungi belonging to the order Pleosporales. These pathogens are widely recognized for causing severe leaf blight and spot diseases on various grass species. Their life cycle is characterized by the production of distinctive, multicellular, fusiform conidia that are adapted for wind and rain splash dispersal.

The primary hosts for Exserohilum species are cereal crops, most notably maize, sorghum, and rice. The fungus attacks leaves, sheaths, and sometimes kernels, causing extensive lesions. By destroying leaf tissue, the pathogen significantly impairs the plant's ability to conduct photosynthesis, leading to reduced yield and poor grain development.

The development of the disease is heavily favored by warm, humid conditions, typically between 20°C and 30°C. The pathogen survives the winter in infected crop debris left on the field or within the seeds themselves. As the season progresses, secondary cycles of infection can occur repeatedly if environmental moisture remains high.

Typical symptoms involve the appearance of oblong or elongated necrotic lesions that are often tan or light brown with a dark border. As the fungal spores develop within these lesions, the centers become covered with a dark, olive-green to black velvety mold. In advanced stages, multiple spots coalesce, causing complete necrosis of the leaf blade.

Management of this disease involves a combination of cultural practices, such as crop rotation, deep tillage to bury infected residues, and the use of resistant crop varieties. Chemical control through the application of fungicides like triazoles and strobilurins during the early stages of disease onset is crucial for minimizing economic losses.