Northern corn leaf blight (Exserohilum turcicum)

Northern corn leaf blight: biology

Northern corn leaf blight (NCLB) overwinters as spores or fungal strands (mycelium) on infected corn leaf residue. Although the fungus overwinters in Ontario, a major source of spores comes from the United States mid-west corn belt and surrounding Great Lakes states. In the spring, spores are moved by wind or rain ‘splashing’ to young plants. Under favourable conditions (moderate temperatures 18°C-27°C with prolonged periods of rain or humidity) the disease forms lesions. During the growing season, secondary spread to other fields occurs by further release and spread of conidia from initial lesions. Losses due to NCLB are most severe when the leaves above the ear are infected at, or slightly after, pollination.

Long, elliptical lesions are often described as cigar-shaped; they are typically large (up to 10 cm or more), greyish-green or tan in colour. The disease develops first on the lower leaves of the canopy and progresses upward on the plant through the growing season. Under severe infection, leaves of a susceptible hybrid can become blighted or ‘burned’ giving the appearance of late-season frost or freeze injury to the plant. The disease is often confused with Stewart’s wilt.