Also known as Helminthosporium leaf blight, foliar blight

Cochliobolus sativus (Ito & Kuribayashi) Drechsler ex Dastur
(anamorph Bipolaris sorokiniania (Sacc.) Shoem.) Shoemaker

Nature of damage

• Depending on environmental conditions, the pathogen causes either spot blotch or common root rot.
• Symptoms caused by C. sativus can be found on sub-crown internodes (common root rot), stems, leaves, and spikes (spot blotch).
• Seedling blight and death may also occur, in particular in wet and warm environments.

Signs

• Spot blotch can be detected as early as three weeks after emergence. If the climate is suitable, the disease develops in severe epidemics, particularly when the crop is around heading.
• Since it is seed transmitted, lower leaves appear more severely damaged. The disease progresses from the lower to upper parts of the plants.
• Lesions on the leaves start as dark brown lesions of a few mm that extend as elongated dark brown spots greater than 1 cm.
• A yellowing due to toxin production is sometimes observed extending from the lesion.
• As the disease progresses the spots join together, forming large blotches that cover the leaves and eventually kill it.

Factors favoring development

• Ideal conditions for spot blotch development on the leaves are relative humidity of near 100% with temperatures of 20°C to 30°C and long periods (>12 to 18 h) of leaf wetness caused by rainfall, irrigation or dew.
• Agricultural practices, such as little or no incorporation of residue into the soil, irrigation, and an imbalance in soil fertility, have lead to an increase in severity.

Geographic distribution

• South Asia, South America, parts of Africa.