Ascochyta leaf spot of paspalum

Pathogen and Disease Type
The disease is caused by the fungus Ascochyta paspali, a member of the Deuteromycetes class. This pathogen induces an ascochyta leaf spot, which is a common fungal infection in various grass species. The fungus propagates through pycnidia—small fruiting bodies that release conidia, allowing the infection to spread rapidly during wet and humid conditions across a field or pasture.

Affected Crops
The primary host for Ascochyta paspali is the genus Paspalum, which includes important forage grasses and turfgrass varieties. While the fungus is specialized to these plants, its presence can be detrimental to pasture productivity and the aesthetic quality of lawns, making it a concern for both agricultural producers and turf managers in regions where these grasses are cultivated.

Symptoms and Signs of Infection
Symptoms typically manifest as necrotic spots on the leaf blades. These lesions start as small pale or yellow spots and gradually enlarge, turning brown with a distinct dark margin. A characteristic sign of the infection is the presence of tiny, black, pimple-like structures (pycnidia) embedded within the center of the necrotic tissue, which confirms the diagnosis of ascochyta blight.

Conditions for Development and Impact
The disease thrives in environments characterized by high humidity, frequent rainfall, and moderate temperatures. Dense canopies that lack sufficient airflow provide the perfect microclimate for fungal spores to germinate and colonize new leaves. The economic impact includes significant reduction in biomass, loss of forage quality, and in severe cases, the potential for total stand thinning if left untreated.

Management and Prevention
Effective management involves cultural practices such as improving field drainage and ensuring adequate spacing between plants to promote airflow. Sanitation is critical; removing or burning infected crop residues reduces the primary inoculum for the next season. When environmental conditions favour an outbreak, the application of systemic fungicides targeting fungal leaf spots is recommended to prevent widespread crop damage.