By Blake Jackson
The first generation of true armyworms is now active and could threaten crops through the end of June, making field scouting a priority for growers.
According to Emily Bick, Pest Ecology for Field and Forage Crops Extension Specialist, and Laura Flandermeyer, Pest Management Outreach Specialist with the University of Wisconsin-Madison, the pest is especially problematic in corn planted into green or recently terminated cover crops.
Alfalfa and small grain fields, particularly those exposed to wind-blown infestations, are also vulnerable.
Producers are encouraged to inspect fields regularly, as feeding damage increases rapidly as larvae mature. In corn fields, scout 100 plants by checking five groups of 20 plants across representative areas.
Look for irregular or ragged feeding on the leaves and inspect the soil around plant bases, especially during midday when larvae tend to hide. Field edges and grassy weed patches should receive extra attention.
For small grains, examine three feet of row in five different locations and shake the plants to dislodge larvae for counting. Record both the number and size of any caterpillars found.
Treatment decisions should be based on established economic thresholds rather than moth activity. In corn, control measures are recommended when 25% of plants contain two larvae smaller than three-quarters of an inch or when 75% of plants have one larva.
In small grains, treatment is advised if three or more larvae are present per square foot.
Natural predators, including ground beetles, parasitic wasps, and red-tailed tachinid flies, can help suppress infestations.
Insecticides are most effective against larvae measuring 0.75 inches or less, while larger caterpillars respond poorly. When infestations are limited, treating only affected border rows can provide effective control while reducing unnecessary pesticide use.
Photo Credit: gettyimages-eugenesergeev
Categories: Wisconsin, Crops, Corn, Alfalfa