Many fungi that cause leaf blight diseases must overwinter on crop residues. Therefore, crop rotation and tillage practices that enhance residue decay before the next corn crop is planted will help reduce diseases such as northern and southern corn leaf blight, anthracnose, eyespot, gray leaf spot, and northern leaf spot. These control methods are generally not effective against the viral diseases or bacterial diseases that require insect vectors for their spread. Fungal diseases spread by wind over long distances also are less effectively controlled by rotation or tillage practices.
Crop rotation is effective only when the disease- causing organism cannot infect the rotation crop. Soybeans and forages are good rotation crops because pathogens that infect corn do not attack these crops. Small grains are also effective in a rotation sequence, although they have some common pathogens with corn. For instance, Gibberella zeae causes head scab and root rot of wheat and ear rot and stalk rot of corn.
When corn is planted year after year in fields maintained with reduced tillage, diseases frequently develop that are of minor importance under tilled and rotated production systems. When it is necessary to use reduced tillage and restricted rotation, it is especially important to select the best resistant hybrids to leaf blight and stalk rot. Under reduced tillage, it will be almost impossible to control certain leaf blight diseases without a rotation away from corn for two to three years. Best control occurs when crop rotation and tillage are used together.
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