Herbicide applications should be over for most fields, unless corn is behind due to late planting. Common corn rust thus far has been minor. Rust thrives in moderate to cool temperatures and high humidity. Luckily, this disease rarely causes economic loss. Recent reports from the Midwest report some northern corn leaf blight showing up.
Infection spreads from the lower leaves, up the plant.
High humidity and moderate temperatures favor the disease. High winds and hail in some locations earlier this season may also spell head smut trouble. The corn seedling was infected when damaged and the disease systemically developed with the plant growth. Tassels of affected plants often show the affects. In some cases, ears may be completely replaced by similar smut masses or an ear may only produce a few kernels.