Sheath blight occurs from seedling stage to heading stage, usually attacking sheaths and leaves, sometimes also stems and heads. Overwintering occurs in the soil and straw. Outbreaks appear mostly when temperature and humidity is high.
- Sheaths – dark green spots appear near the water surface, and may expand into oval lesions, finally fused into more big scabs. When it is dry, scabs are hoary in the center with dark brown color on outer side; when it is wet, scabs are celadon in the center and dark green on outer side. At high temperatures, white mold powder might be observed on scabs (Fig 1).
- leaves – similar scabs with irregular shaped.
- stems – at an early stage stems may show similar symptoms than leaves, at a later stage scabs have a tawny color and stems are easily broken.
- heads – at lower infestation rates, scabs are taupe and heads show reduced grain formation. At high infestation levels, plants don’t produce heads and finally wither (Fig 2).
Cultural control: Remove sclerotium from infested fields by plowing in autumn and manage irrigation, i.e. keep “shallow, dry, wet” steps to avoid over watering or over drying. Ensure balanced fertilization and avoid over-use of nitrogen. Increase plant spacing to avoid horizontal spread of the disease
Chemical control: See Green & Yellow List for details.