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College of Food, Agricultural, and Environmental Sciences


Scout Fields Weekly for Best Insect Control

May 23, 2006

WOOSTER, Ohio -- Ohio growers should be scouting their fields on a weekly basis to assess the level of populations and subsequent damage from a myriad of pests now making an appearance in corn and soybean fields.


"IPM (Integrated Pest Management) recommendations include growers scout their fields weekly from emergence to harvest," said Ron Hammond, an Ohio State University research entomologist with the Ohio Agricultural Research and Development Center. "This is a normal time of year for us for pests, but one concern we have right now is the cool, wet weather that has slowed crop emergence and increased the susceptiblility to injury."

The biggest threat is feeding from juvenile slugs, which have already damaged some no-till crop fields in southern Ohio, and are beginning to feed in fields throughout northern Ohio. The longer it takes from plants to emerge from the soil and begin growing, the more susceptible to feeding injury they become.

"With the cold, wet weather we had the last two weeks, the crops just aren't growing as well," said Hammond. "We are hoping for dry, warm weather so that these crops can really take off. Who will win out at this point in time -- the slugs or the crops?"

Hammond said growers should also be scouting for corn flea beetle, which can transmit Stewart's bacterial blight causing seedling wilt and leaf blight.

"As predicted, we are seeing higher populations of corn flea beetle in parts of Ohio. Growers should be checking newly emerged plants for flea beetle activity," said Hammond. "Treatment is warranted if 3 percent or more of the plants are wilting, dying or showing signs of severe feeding."

Entomologists are also reporting injury in corn from black cutworms, which can cause seedling loss and stalk injury in situations of heavy feeding.

Turning to alfalfa, Hammond said that growers should have their eyes on potato leaf hopper.

"We are getting beyond the concern for alfalfa weevil, but growers should begin sampling their fields for potato leaf hopper," he said. "The insect could become a problem as alfalfa starts to re-grow anywhere from three to five inches after its first cutting. The pest has arrived from southern states and we know that it's in apple trees where the first generation builds up."

During the next few weeks, armyworms may become an important pest to watch for, said Hammond.

"Armyworm moths were collected in larger-than-normal numbers in Ohio and surrounding states. These larger moth numbers mean that we will need to closely monitor wheat and then adjacent cornfields, along with no-till cornfields, over the next month for possible economic larval populations," said Hammond.

The larval stage of the armyworm is the most destructive to the corn crop. Severe infestations can cause defoliation of entire stands of corn. In some cases, the injury is so devastating that only mid-ribs of the corn plant remain and a field can be reduced to stubble.

"A big concern is that we have become aware of recommendations being made by others suggesting wheat fields be sprayed with a pyrethroid insecticide, not to control the larvae, but to prevent adult armyworms from entering the field and laying their eggs. There are no data we are aware of that indicate repellency towards armyworm adults, so we do not recommend that growers use this tactic," said Hammond. "Also, we would point out that this is not a proper IPM approach. The best way to manage armyworms is by scouting for the larvae and treating when they reach established thresholds."

For more information on pests that affect field crops, log on to Ohio State's Agronomic Crops Team Web site at


Candace Pollock
Ron Hammond