Bromegrass leaf spot

The disease is caused by the ascomycete fungus Pyrenophora bromi, which is the teleomorph of Drechslera bromi. It is a significant foliar pathogen that affects various species of the Bromus genus. In agronomy, it is recognized as one of the primary limiting factors for high-quality forage production in many temperate regions.

The primary host for this pathogen is smooth bromegrass (Bromus inermis). While other grass species may exhibit symptoms, the disease is most economically damaging in cultivated bromegrass fields intended for hay and silage production, where it can spread rapidly throughout the dense canopy.

Symptoms initially manifest as small, brown-to-black spots on the leaves. As the infection progresses, these spots elongate and develop into distinct, dark brown lesions surrounded by a yellow chlorotic halo. Under favorable conditions, these lesions coalesce, eventually causing the entire leaf to turn brown, wither, and die prematurely.

The development of the disease is heavily dependent on environmental factors, particularly high humidity, frequent rainfall, and temperatures ranging from 15°C to 22°C. The fungus survives the winter as mycelium or pseudothecia on crop debris and stubble, which serve as the primary inoculum source for the following season.

The pathogenicity of Pyrenophora bromi leads to a substantial reduction in dry matter yield and a decrease in the nutritional quality of forage. Infected leaves contain lower levels of protein and digestible nutrients, rendering the hay less valuable for livestock feed. Severe infestations can also lead to reduced plant vigor and long-term stand decline.

Integrated management is essential for controlling this disease. Key strategies include:

• Implementing crop rotation to break the disease cycle.
• Removing or burying crop residues through deep plowing.
• Planting disease-resistant cultivars of bromegrass.
• Managing pasture density to ensure better air circulation and leaf drying.