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, residue management through 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 corn, extra care must be taken to select disease-resistant hybrids. A high incidence of leaf blight can cause early death of plants, increase stalk lodging, and move harvest dates ahead; the incidence of stalk rots increases in blighted fields. Delayed harvest leads to greater field losses through reducing grain quality, grain yield, and increased lodging. Harvest dates should be determined by crop maturity and grain moisture. If a field is blighted with severe ear rots, it may be economical to harvest at higher grain moisture and dry the grain to halt the infection rather than waiting for natural dry down.
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 after tasseling are from the ear leaf and farther up the stalk. As lesions increase on these photosynthetically active leaves, the amount of carbohydrates produced and transferred to the plant grain decreases. 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 rarely occur. The advancement of genetic resistance and the use of crop rotation has have 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.
