Rainfed rice - IRRI books - International Rice Research Institute

Sheath blight
(caused by Rhizoctonia solani )
The fungal pathogen has a wide host range,
attacking other crops after or before rice. Many
weeds in the ricefields also host the pathogen.
Fruiting bodies (sclerotia) of the fungus remain in
the soil and serve as the primary inoculum for
disease initiation.
Disease Management Strategies
The disease is favoured by high nitrogen and phosphorus and high plant density.
In general, modern cultivars lack resistance against sheath blight. Losses occur
because of poorly filled grains, increased lodging and reduced ratoon production.
Symptoms
Spots or lesions of greenish grey, elliptical or oval and about 1 cm form mostly on
the leaf sheath. The spots first appear near the waterline in fields. Infections
spread rapidly under low sunlight, high humidity and high temperatures between
28 and 32°C.
Control measures
Apply green manures such as dhaincha and sunhemp to reduce primary
inoculum and disease severity.
Sanitise the field properly.
Balance the application of fertilisers.
Do not use long rotation without a non-host crop.
Foliar application of chemicals such as carbendazim, vitavax and topsin M (0.5
kg a.i./ha) reduces disease under field conditions. Two fungicide applications
are necessary.
Use resistant varieties, if available.
Use crop rotation with legumes.
Seed treatment with 100 g turmeric powder and 1 g asafoetida powder/10 g
sodium bicarbonate followed by foliar spray of captafol 80% at 1.5 kg/ha or
carboxin 500 g/ha or benomyl 500 g/ha at ETL of three cobra spots on the leaf
sheath in three tillers of three random plants.
Use available biocontrol agents for soil treatment (500 g/ha), such as
Trichoderma viridis or T. harzianum alone or in combination with green manure.
False smut
(caused by Ustilaginoidea virens )
Symptoms
The rice kernels are replaced by globose, velvety spore balls
(sclerotia), 1-5 cm in diameter, which burst out from
The disease has
become important
with the introduction of
high-yielding varieties.
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