Armyworms

Bryan Jensen, Dept. of Entomology and IPM Program

Armyworms might be something you want to keep an eye open for during the next few weeks. No major concerns have been reported. This is just a heads up.

First generation armyworm larvae are hard to predict in terms of timing, location and severity. However, it is that time of the year when I would scout fields which have the greatest likely hood of damage. In wheat (and other small grains) it is especially hard to anticipate. Areas with dense cover and perhaps areas with lodging might be worth concentrating scouting efforts on. Armyworm feed on foliage but can also clip heads. Treatment is suggested if you find an average of 3 armyworms per square foot in small grains.

In, corn I would suggest concentrating scouting efforts on fields that are no-tilled into alfalfa, had a small grain cover crop or early season grass weeds. In corn, treatment can be suggested when 25% of the plants have two or more larvae/plant or when 75% of the plants have one larvae/plant. Treatment would not be suggested if larvae are greater than 1 ¼ inch in length. Those larvae will be pupating soon and very little additional defoliation would be expected. Certainly not enough to pay for an insecticide application.

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