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Northern
Corn Leaf Blight has traditionally been one of the most damaging corn leaf
diseases. Use of resistant hybrids has limited yield losses from this disease in
commercial corn. The
disease appears as long, elliptical (2-15 cm (1-6 in.)) grayish-green or tan
streaks. Lesions most often begin on the lower leaves. As the disease develops,
individual lesions may join, forming large blighted areas. In some cases the
entire leaves may become blighted or "burned." Losses due to northern
leaf blight are most severe when the leaves above the ear are infected at or slightly
after pollination. The disease is often confused with Stewart's Wilt. The
fungus survives in corn residue as either spores or fungal strands (mycelium).
The spores of the fungus are spread from the ground residue to the developing
corn plant through wind or rain "splashing." Plants that become
infected act as a secondary source of infection and may spread to other fields.
Disease development is favored by moderate temperatures (64°F-81°F) with
prolonged periods of humid or rainy weather.
Northern
corn leaf blight exists as four races, and most of the commercial corn hybrids have
resistance or tolerance to the most common races that occur. Crop rotation and
tillage will reduce inoculum levels in surface residues. In reduced tillage
systems, rotation and resistance are necessary. Chemical control is not usually
economical in field corn.
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