Rice Sheath Rot

Disease

Rice Sheath Rot

Sarocladium oryzae

fungi

In a Nutshell

    Spot-like lesions developing on the uppermost leaf sheaths that enclose the paniclesRotting of the sheath and development of whitish powdery fungal growthGrains of emerged panicles become discolored and steril

Hosts: %1$s

· Rice

Symptoms

Early symptoms are oblong to irregular spots on the leaves (0.5 to 1.5 mm) that enclose the panicles. Spots are characterized by gray centers and brown margins and are often combining to form rotting and then discoloration of the leaf sheaths. In severe infections, the young panicles may not emerge. Affected leaf sheaths may have abundant whitish powdery fungal growth visible on the outer surface. Grains of emerged panicles become discolored and sterile. Unemerged panicles produce florets that turn red-brown to dark brown. Infection is most damaging when it occurs at late booting stages and can cause severe damage.

Trigger

Sheath rot is principally a seed-borne disease. The disease is caused principally by the fungus Sarocladium oryzae but also in some cases by Sacroladium attenuatum. Its incidence increases with increasing planting density and in plants that provide entry points for the fungus, in the form of injuries and wounds caused by insects at panicle initiation stage. The application of potassium, calcium sulphate or zinc fertilizers at the tillering stage strengthen the stem and leaf tissues and thus avoid extensive damage. It is also associated with plants weakened by virus infections.Hot (20-28°C) and humid (wet) weather favour the growth of the disease.

Biological Control

Bacteria such Rhizobacteria of Pseudomonas fluorescens isolated from citrus and rice are toxic to the rice sheath rot fungus, resulting in lesser incidence and more yield. Bipolaris zeicola is another potential antagonist of sheath rot that can completely inhibited mycelial growth of S. oryzae. Antifungal activity of extracts from leaves and flowers of Tagetes erecta also inhibit S. oryzae mycelium by 100%.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatments if available. In case of severe infestation, the application of fungicides such as benomyl, carbendazim, mancozeb, copper oxychloride or propiconazole have been shown to reduce the incidence of the disease. Application of a seed treatment fungicide like carbendazim, edifenphos, or mancozeb at rates of 3g/kg of grain before sowing is also effective.

Preventive Measures

    Use certified healthy seedsUse wider planting distance of 25cm x 25cmAvoid monocultures in same field, use at least two varietiesSurvey the fields regularly for insects pests like panicle miteApply potassium, calcium sulphate or zinc fertilizers at the tillering stageRemoval of infected stubbles and weeds from the field also helps




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