Corn Northern Leaf Blight

 


Northern corn leaf blight (NCLB) is caused by the fungus Setosphaeria turcica. Symptoms usually appear first on the lower leaves. Leaf lesions are long (1 to 6 inches) and elliptical, gray-green at first but then turn pale gray or tan. Under moist conditions, dark gray spores are produced, usually on the lower leaf surface, which give lesions a "dirty" gray appearance. Entire leaves on severely blighted plants can die, so individual lesions are not visible. Lesions may occur on the outer husk of ears, but the kernels are not infected. On hybrids that contain an Ht gene for resistance to the fungus, lesions are smaller, chlorotic, and may develop into linear streaks. These lesions rarely produce spores.

Lesions can eventually expand to a more oblong or “cigar” shape. They may also coalesce to form large areas of necrotic tissue. Dark spores may be observed in the lesions with the aid of a hand lens. Symptoms often begin on lower leaves; spores produced by primary lesions are carried by wind or rain splash to upper leaves. Lesions may also form on husks. Loss of photosynthetic tissue can result in decreased yield, and silage quality can be affected.



Management and Control

Control of this disease is often focused on management and prevention. First, choose corn varieties or hybrids that are resistant or at least have moderate resistance to northern corn leaf blight. When you grow corn, make sure it does not stay wet for long periods of time. The fungus that causes this infection needs between six and 18 hours of leaf wetness to develop. Plant corn with enough space for airflow and water in the morning so leaves can dry throughout the day. The fungus overwinters in plant material, so it is also important to manage infected plants. Tilling the corn into the soil is one strategy, but with a small garden it may make more sense to just remove and destroy the affected plants. Treating northern corn leaf blight involves using fungicides. For most home gardeners this step isn’t needed, but if you have a bad infection, you may want to try this chemical treatment. The infection usually begins around the time of silking, and this is when the fungicide should be applied.



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