Sheath net blotch

Sheath net blotch, caused by the fungus Calonectria morganii (also known as a stage of the Cylindrocladium complex), is a significant plant disease that primarily attacks the sheath tissues of host plants. As a necrotrophic pathogen, it extracts nutrients from the plant cells, leading to localized tissue death and structural weakness.

The primary crop affected by this pathogen is rice (Oryza sativa). While it can be found in various environments, it is most prevalent in regions characterized by high humidity and intensive cultivation systems where moisture remains constant at the base of the plant canopy.

The symptoms of the disease typically appear as small, irregular lesions on the rice leaf sheaths. Over time, these spots expand, often developing distinct margins with necrotic centers. As the disease progresses, the coalescing lesions cover the entire sheath, causing the plant to weaken and significantly impacting the filling stage of the grains.

Development of Sheath net blotch is driven by favorable environmental factors. The fungus thrives under conditions of high humidity, frequent rainfall, and warm temperatures. These conditions facilitate the release and spread of spores within the field. Because the fungus is soil-borne and residue-borne, it can survive between cropping cycles, making the field environment a reservoir for infection.

To mitigate the impact of the disease, growers should employ a multi-faceted management strategy. Cultural practices, such as removing crop debris and managing irrigation to ensure adequate drainage when possible, are essential. Furthermore, the application of registered fungicides is recommended when disease pressure exceeds the economic threshold, ensuring that the crop's physiological development remains protected until maturity.