Bipolaris leaf spot

Bipolaris leaf spot is a common fungal disease of grasses caused by the pathogen Bipolaris cynodontis. This fungus primarily affects various turfgrass species, including Bermuda grass, causing significant aesthetic damage and reducing the overall health and vigor of the sward.

The host range of Bipolaris cynodontis is quite broad within the Poaceae family. The fungus survives unfavorable conditions as dormant mycelium or spores in infected debris, thatch, or within the soil profile, waiting for favorable temperatures and moisture levels to initiate a new infection cycle.

Symptoms typically begin as small, dark brown or black spots on the leaves. As the infection progresses, these spots expand, often forming a necrotic halo, which leads to leaf yellowing (chlorosis) and eventual browning. Severe infestations can cause thinning of the turf and widespread blighting of foliage.

The development of this disease is highly dependent on environmental factors, particularly extended periods of leaf wetness and moderate to warm temperatures (20°C to 30°C). High humidity levels and improper irrigation practices, such as late evening watering, create an ideal microclimate for fungal spore germination and penetration.

To effectively manage Bipolaris leaf spot, an integrated pest management strategy is essential. This includes improving soil drainage, reducing thatch buildup, and ensuring balanced fertilization to avoid excessive succulent growth. Fungicide applications, specifically those containing azoxystrobin or other effective systemic compounds, are recommended when symptoms first emerge to prevent significant damage.