April 2, 2003 | By: Laura Skillman

A number of Kentucky farmers are planting corn in the same field for more than a year, and with this single cropping system comes the increased chance of more disease and insect problems.

“Listening to growers in winter meetings, I have heard some indicate they have given up the traditional 50-50 split of corn and soybeans,” said Ric Bessin, University of Kentucky Extension entomologist. “Some are going as high as 80-20 in favor of corn. While this may be a good marketing decision, it will create some new insect management issues.”

Farmers need to look carefully for rising corn rootworm populations in their continuous cornfields, he said.

“It is a very destructive pest that is almost completely controlled through crop rotation,” Bessin said. “For farmers opting for continuous corn, they need to watch for western corn rootworm. The eggs laid in last year’s corn fields will hatch in late spring and the larvae will feed on the root systems of corn plants. A second year of corn only increases the risk slightly, but each year a single field is kept in corn increases the chances of an economic loss as the result of this insect.”

Bessin said farmers should use a soil insecticide if growing continuous corn and if they noticed an average of at least one beetle per plant last summer. No soil insecticide is needed for rootworms in fields where something other than corn was grown last year. There are no rescue treatments, he noted. When symptoms of corn rootworm damage appear it is too late to take corrective measures.

For those farmers opting to grow corn after corn, it is important to understand and recognize that this practice will increase the disease potential over a period of several years, said Paul Vincelli, University of Kentucky Extension plant pathologist.

“The disease that I can predict will increase on virtually every farm growing corn after corn is gray leaf spot,” he said. “This disease overwinters in corn residue, so when you grow continuous corn you give the fungus that causes gray leaf spot a chance to grow and build up in that field.”

It is very important to select hybrids that have partial resistance to gray leaf spot when growing corn after corn, Vincelli said.

Another disease of significant concern when growing continuous corn is diplodia ear rot. It can cause mold, decomposition and rotting of the grain in the field. Diplodia ear rot can be easily identified because when the husk is peeled back it will show mold growth between the kernels often consuming the whole ear. Diplodia infections usually progress from the base of the cob upward, which helps further in disease recognition in the field.

The fungus that causes diplodia ear rot also overwinters in corn residue, Vincelli said. It will not be as widespread as gray leaf spot but is a very destructive disease of certain hybrids so it is important to monitor for this disease and check for it at the end of the season.  If as little as 2 to 3 percent of the ears are infected with diplodia ear rot it is very important to either rotate or use a hybrid that has been bred to be resistant to the disease.

“This disease can explode from a very little level to a very high level the next year on a susceptible hybrid under the right weather conditions,” he said. “It can be a potentially very destructive disease under continuous corn and it is one to watch out for.”



Ric Bessin, (859) 257-7456; Paul Vincelli, (859) 257-5675