June 28, 2006 | By: Aimee Nielson

Some corn producers may be considering using foliar fungicides to thwart disease this year. University of Kentucky College of Agriculture Plant Pathologist Paul Vincelli said, however, that most Kentucky corn fields will not benefit from the application of a fungicide.

“There are cases every now and then where an application may be economically justified,” he said. “The difficulty is identifying these cases in advance because disease development is so dependent on the weather that it’s difficult to be confident in knowing when a given corn field will benefit economically from application.”

Two diseases that might prompt corn producers to use a fungicide are gray leaf spot and northern leaf blight. Gray leaf spot is a common concern each year, while northern leaf blight is not usually a problem this far south.

“We had an unusually cool, wet summer in 2004 and northern leaf blight became epidemic in many fields in Kentucky and surrounding regions,” Vincelli said. “There is a risk of carryover of some inoculum in those fields, assuming they are back in corn after a rotation to soybeans last year.”

Vincelli said there are some things to consider when determining whether applying fungicides will be profitable in the long run. Crop rotation, tillage and hybrid susceptibility are the most important factors that influence gray leaf spot and northern leaf blight development. Late planting also increases disease pressure. A field with good air movement will have less disease pressure than a foggy field on a creek, he said. 

Getting adequate coverage of the plant’s leaves is also a factor to consider, so it’s important to make sure the spray provides good coverage of the foliage from the ear leaf on up. Vincelli said that if producers apply fungicide, it’s best to do so in a single, well-timed application at or near tasseling.

“Foliar fungicides applied to corn can provide some protection against yield losses that range from zero bushels per acre to 40 bushels per acre,” he said. “In other words, some producers may see no benefit to using a fungicide, even in high-risk fields, while another producer may avoid a 20 to 40 bushel per acre loss. There is just no way to know ahead of time if a producer will get back more than the cost of application, since it depends on so many factors like weather, disease buildup, corn prices and so on.”

Vincelli emphasized that fungicides do not increase yields. All they can do is protect the yield potential of the field from losses due to one or more diseases. 

“The bottom line, in my judgment, is that there are few instances where fungicide will be an important part of a disease management program for corn production in Kentucky,” he said. “Its principal use is probably in specialty corns where the hybrid is susceptible to gray leaf spot, a premium is being placed on grain quality and the field is at moderate to high risk. It probably has value in the few seed production fields in Kentucky. Given the rotation practices of most farms and the hybrids available this season, most typical grain fields won’t benefit much, if at all, from fungicide use.”

Producers who are unsure about the level of gray leaf spot pressure in their county should contact their local county Extension agent for more information.


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