True armyworm poised to threaten crops
To scout, farmers need to look near the ground in pastures and fields.
"You really have to scout in late afternoon or early morning or on cloudy days. You have to get down and look through the leaf litter on the ground and at the lower leaves of the plant," Bailey said. "You are looking for areas that have been eaten with very smooth edges, and for larvae."
The economic threshold at which it becomes profitable to spray insecticides depends on the number of worms. If there are more than four half-grown worms per square foot in grass pastures or wheat fields, farmers should consider spraying.
"There's no substitute for good scouting in field and forage crops," Bailey said. "Corn and wheat can be treated with several classes of insecticides, but on fescue and other grasses the options are limited to Sevin, Malathion, Mustang Max, Warrior II, plus two biological insecticides."
Pre-harvest intervals-the time between spraying and grazing or haying-range from zero to 14 days, depending on the insecticide.
Read more about true armyworm and treatment in the MU Integrated Pest and Crop Management newsletter at ipm.missouri.edu/IPCM/index.cfm?ID=293 or in the MU Extension guide at www.extension.missouri.edu/G7115.