Over the past 5 years, Northern Corn Leaf Blight (NCLB) has become a common occurrence in field and sweet corn in New York State. Researchers at Cornell University are working to determine why this disease has become more prevalent. Current hypotheses include: 1) new races of the fungus, 2) new corn hybrids may be more susceptible, 3) weather patterns that favor disease, and 4) changes in the larger cropping picture. There may be a sort of an "arms race" between new races of the fungus and new corn hybrids. Western NY has seen an increase in field corn being grown and increased disease in field corn creates additional inoculum for sweet corn in the region. If NCLB becomes severe, yields may be reduced. Fresh market sweet corn growers may also be concerned with lesions that appear on the husks, as the corn may be less marketable.

The fungus Exerohilum turcicum that causes NCLB survives as spores or mycelia on corn debris over the winter. The inoculum can be splashed onto the current corn crop or can arrive by wind. The spores can be moved long distances by wind. Early infections come from within the field and are more damaging. As the season progresses and the numbers of spores in the air increases, all fields become susceptible. Infection is favored by leaf wetness and cool weather (64-81 F) as typically occurs later in the growing season.

Lesions of NCLB begin as grayish green and become tan as they mature. The slender oblong shape, with tapered ends, gives them a cigar or boat-shaped appearance. Lesions range from 1 to 6 inches in length and may coalesce to cover the entire leaf. Spores are produced on the underside of the leaves, and appear as dusty green fuzz.

Resistant varieties and cultural practices to reduce inoculum and disease risk are the best practices. Fields should be scouted whorl through tassel. There is a scouting video for field corn developed by the NYS IPM Program (see list of resources below). Several fungicides are labeled and a listing can be found in the Cornell Vegetable Guidelines. 

ADDITIONAL RESOURCES

NYS IPM Scouting video:



Cornell NCLB fact sheet includes lists of fungicides and their relative effectiveness. Note: check labels for sweet corn.

Vegetable MD Online, Sweet Corn Diseases