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.