Diseases

Part 2, Section 2: Corn Pest Management

Corn Pest Management

DISEASES

Corn diseases are strongly influenced by weather conditions and are difficult to predict. Most diseases in Pennsylvania are best controlled by using resistant hybrids and a balanced fertility program. Since major corn pathogens can overwinter in Pennsylvania, tillage and crop rotation are common cultural practices for reducing sources of disease-causing organisms, particularly if disease was a problem the previous year.

In no-till plantings of continuous corn, extra care must be taken to select disease-resistant hybrids. A high incidence of leaf blight causes early death of plants and moves harvest dates ahead; stalk rots increase in blighted fields. Delayed harvest leads to greater field losses. Harvest dates should be determined by crop maturity, not by the calendar.

As with most agronomic crops, it is important to realize that not all diseases cause economic losses and the timing of occurrence is as important as the disease. In corn, the most important leaves to protect are from the ear leaf and further up the stalk. As lesions increase on these photosynthetically active leaves, the amount of carbohydrates produced and transferred to the plant decrease. In severe cases of Gray Leaf Spot, lodging will increase because the plant has pulled all of the nutrients out of the stalk to devote to grain fill. Fortunately for Pennsylvania, these conditions occur rarely. The advancement of genetic resistance and crop rotation has reduced many of the yield limiting diseases that would benefit from fungicide applications. Disease prevention or control with fungicides other than seed treatments is usually not economical and should be considered only on an individual basis.