Fall Armyworms and Army Cutworms Active

Fall armyworms began arriving in Kansas in mid-June and pheromone trap counts continue to increase state-wide during September (Figure 1).

Another potential fall pest, army cutworms, have been detected in traps in western Kansas since the beginning of September. Army cutworms are late fall and early spring pests of several Kansas crops, including alfalfa, wheat and triticale. These moths begin migrating into Kansas in the fall from their over-summering locations in the Rocky Mountains. Trap counts of 800 or more army cutworm moths in an area through October may indicate significant caterpillar activity the following spring. Currently, northwest Kansas has the highest number of moths being trapped weekly (Figure 2). Female moths can lay up to 1000 eggs or more. After hatching, caterpillars will begin feeding until cold weather forces them below ground. Caterpillars will complete their growth next spring as weather warms and then burrow into the soil to pupate. Sexually immature adults emerge in late spring and migrate back to the mountains for summer. This is the “miller moth” flight that can be a nuisance some years during the spring.

Given the presence of these two pests and continued warmer weather in the forecast, at-risk fields should continue to be scouted weekly for caterpillar activity. In the case of army cutworms, caterpillars may be small and hard to find; pay close attention for window-pane damage on young plants (Figure 3).

Keep in mind that caterpillars increase in size at an exponential rate and most of the feeding occurs during the later stage of development. It is critical to scout early and treat, if needed, when the caterpillars are less than a half-inch long. Larger caterpillars are harder to control and do the most damage. Arrival of cooler weather may help to slow down caterpillar activity and development.