Teleomorph: Cochiliobolus heterostrophus
(Anamorph: Bipolaris maydis, syn. Helminthosporium maydis)

Nature of damage

• Damage is caused by loss of photosynthetic leaf area, due to foliar lesions which reduce photosynthate production for grain filling.
• Further damage is caused by lodging, which occurs when plants divert sugars from the stalks for grain filling during severe disease pressure.

Signs

• Young lesions are small and diamond shaped. As they mature, they elongate.
• Growth is limited by adjacent veins, so final lesion shape is rectangular and 2 to 3 cm long.
• Lesions may coalesce, producing a complete burning of large areas of the leaves.

Factors favoring development

• Continuous maize cultivation.
• Conditions favorable to the overwintering of fungi in infected crop debris.

Geographic distribution

• Maydis leaf blight is found in all tropical and temperate maize growing regions where the growing season is characterized by warm and wet conditions.