June 20, 2007 | By: Laura Skillman

Questions about the need for and possible advantages of using fungicides on corn arise every year, but with the upswing in additional corn acres this year, more growers are likely searching for answers.

“The principal diseases that might justify a fungicide treatment in some fields are gray leaf spot and northern leaf blight,” said Paul Vincelli, plant pathologist with the University of Kentucky College of Agriculture. “Both of these are caused by fungi that overwinter in corn residues of leaf blades and sheaths, so they are naturally more severe when corn follows corn under conservation tillage.”

Unfortunately, there is no formula for deciding whether a fungicide application to field corn will provide an economic return. Producers must think in terms of probability, just like rolling a set of dice. There are many uncertainties that need to be addressed with more field research. However, Vincelli said, as more information is sought through research trials, it is probably useful to consider the experiences researchers and producers have had with fungicide use on soybeans. There are many similarities between soybean fungicides and the use of fungicides on corn.

In soybeans, yields are enhanced about 60 percent of the time with the use of fungicides, he said, but it’s only profitable 28 percent of the time. Farmers must decide if that is often enough to consider spraying a soybean field.

“I suspect the results in corn are going to be similar,” Vincelli said. “In soybeans we don’t have guidelines when deciding whether a particular field would benefit. In corn the situation isn’t quite so dire.”

Several factors increase the likelihood of disease problems. These include growing a variety susceptible to gray leaf spot or leaf blight, growing continuous corn or no till corn, late planting, irrigation, disease activity at tasseling and disease-favorable weather. The more risk factors that apply to producers’ fields, the more likely they are to have an economical yield increase for fungicide in corn. High-yield potential and high-value specialty corn also increases the likelihood of a positive economic return from fungicide use. 

“My recommendation is if you are interested in trying a fungicide, try it out,” Vincelli said. “But always, always leave a check strip for comparison. Then put a pencil to the economics after you harvest both strips.”


Paul Vincelli, 859-257-7445, ext. 80722