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College of Food, Agricultural, and Environmental Sciences


Weather Slowing Corn, Increasing Chances for Pest Problems

May 29, 2008

WOOSTER, Ohio -- Planting delays and cool weather have slowed corn development, paving the way for a potential issue with slugs in no-till fields.

Slugs are pests that can make a meal of young corn plants in the spring, impacting plant performance and reducing yields. And with only a little over half of the corn crop planted, coupled with shorter-than-normal stalks, the plants have become an easy target.

"We always seem to have slugs each year, but it isn't so much that the slugs are any more numerous this year. When you only have a certain number of plants emerged and they aren't very tall, the slugs have the upper hand," said Ron Hammond, an Ohio State University Extension entomologist. "Normally these plants are a lot taller this time of year, but with the rains, we have planted late, and the cooler temperatures are slowing plant growth."

The juvenile stage of the slug creates the most damage to crops and its voracious appetite can be devastating for farmers who have had a history of slug problems. Upon hatching in mid-to-late May, the slug will begin feeding on anything that is planted in the field, whether it's corn, soybeans or alfalfa.

Hammond recommends that growers scout their fields for slugs and treat if necessary.

"A lot of fields have already been treated and that's the most we've seen for quite a few years," said Hammond, who also has an appointment with the Ohio Agricultural Research and Development Center. "With so much corn just being planted in areas where slugs are already present, it's going to be a tough situation. It's all about timing and we are hitting it at the worst time."

In addition to slugs, corn growers may also be facing unusually high populations of armyworms this year.

Hammond said that the pest is not generally a problem for Ohio growers, but when large numbers migrate from the south, the potential exists for heavy feeding and subsequent damage to both wheat and corn.

"Armyworms migrate from the south in late March and April, and if they come up in big numbers, we have the potential for damage. We've been receiving reports from Kentucky and southern Indiana that armyworm populations are the largest that have been recorded in a long time," said Hammond. "The good situation for Ohio is these large numbers help us to determine what kind of a problem we could have."

The biggest concern from armyworm damage comes especially from planting corn into a ryegrass cover crop, said Hammond.

"Armyworms like to lay their eggs on grasses, particularly ryegrass, and that's a major cover crop in Ohio. When growers kill off that ryegrass in the spring, the larvae will move over to the corn. We can see complete devastation of a cornfield planted into a rye cover crop," said Hammond. "Another situation is when armyworms finish feeding on wheat. They will move out of the field to the nearest crop, which often tends to be corn."

Like slugs, growers should also be scouting their cornfields for armyworms and treating when necessary.

"The critical time is now for corn growers to get out in their fields to prevent getting caught by an insect problem that is now rearing its ugly head," said Hammond.

According to the Ohio Agricultural Statistics Service, only 64 percent of the corn crop has been planted. Normally by this time, nearly the entire crop is in the ground.

For the latest developments on Ohio's field crops, refer to the OSU Extension Agronomy Team Web site at

Candace Pollock
Ron Hammond