Exserohilum leaf spot

The disease known as Exserohilum paspali leaf spot is caused by the pathogenic fungus Exserohilum paspali. This pathogen is highly specific to grasses, particularly the Paspalum genus, and acts as a significant threat to both agricultural fodder and turfgrass landscapes worldwide.

Plants affected by this fungus typically include forage grasses and various turf species used for landscaping and sports fields. The disease is particularly damaging in environments where these grasses are grown as a dense canopy, which provides an excellent substrate for the fungus to establish and persist over several growing seasons.

Symptoms initially appear as small, elongate, dark brown or reddish-brown lesions on the leaves. As the infection progresses, these lesions expand and coalesce, eventually causing large areas of the leaf to necroticize and turn brown. Under high humidity, a characteristic greyish-black layer of fungal sporulation may become visible on the surface of the lesions.

The epidemiology of Exserohilum paspali is driven by temperature and moisture. Optimal conditions include temperatures between 20°C and 28°C and high humidity levels. The fungal conidia are dispersed by wind and splashing water, meaning that irrigation practices and rainfall events significantly influence the rate of disease progression throughout the season.

Effective management strategies should focus on an integrated pest management (IPM) approach:

• Promoting air circulation to lower humidity within the turf canopy.
• Reducing leaf wetness duration by adjusting irrigation schedules to morning hours.
• Sanitation practices, including the removal of infected clippings.
• Application of appropriate systemic fungicides when disease pressure is high.
• Maintaining proper soil fertility to ensure the plant can withstand infection pressure.