Rice Stem Rot
Symptoms are usually seen after the tillering stage. Initial symptoms are small, irregular black lesions on the outer leaf sheath near water level. As the disease advances, the lesion enlarges, penetrates the inner leaf sheath and the culm, producing brownish-black lesions. One or two internodes of the stem eventually rot and collapse (only the epidermis remains intact), leading to lodging, unfilled panicles, chalky grains or death of the tiller. Dark-greyish mycelium can be seen inside hollow, infected stems, with small, black sclerotia dotted over the inner surface.
Infection is high on plants with wounds as a result of lodging or insect attack. The panicle moisture content and nitrogen fertilizer also influence disease development.
Methods to control stem rot include good field management practices, and the use of antagonistic organisms.
Always consider an integrated approach with preventive measures together with biological treatments if available. Chemicals such as fentin hydroxide sprayed at the mid-tillering stage, thiophanate-methyl sprayed at the time of disease initiation can reduce stem rot incidence. Other fungicides such as ferimzone and validamycin A also work effectively against the fungus.