This fall after wheat is planted and any new stands of alfalfa are established, farmers will need to scout those fields for grasshoppers, fall armyworm, armyworm and any feeding damage on seedling plants.
Fall armyworms do not overwinter in Kansas in any significant numbers. Thus, after these larvae (worms) pupate in the soil and emerge as adult moths, they will head south for overwintering. Armyworm moths do not migrate south for the winter, but continue to feed on plants until temperatures get cooler, then overwinter in a protective cocoon in the soil.
Army cutworm moths, on the other hand, lay their eggs on the soil in the fall, and the larvae remain active throughout the winter, emerging to feed above ground in warm spells, and hiding deeper in the soil when it is cold. So, it is important to properly identify any worms feeding in wheat or seedling alfalfa, as armyworms and fall armyworms will not feed through the winter and early spring, but army cutworms will.
Keep in mind that, if growing conditions are favorable for fall planted wheat, it can withstand quite a bit of armyworm feeding and continue to grow. However, if growing conditions are not favorable, considerable feeding may severely reduce the stand.
Fall armyworm counts from pheromone traps steadily increased through August, particularly in central and eastern Kansas, with reports of egg masses in residential and agricultural settings. At-risk crops should be scouted regularly for the remainder of the growing season, says K-State Research & Extension Entomologist Anthony Zukoff. Caterpillars increase in size at an exponential rate and a majority of feeding occurs during the last larval stage. It is critical to scout thoroughly and treat, if needed, before the caterpillars are over ½ inch long. Larger caterpillars are harder to control and do the most damage, says Zukoff.
Fall armyworm thresholds for fall planted crops
• Alfalfa: 1-2 caterpillars per square foot can destroy seedling alfalfa. 10-15 per square foot can destroy 12” tall plants.
• Wheat: Larval “window-paning” in early planted wheat can be a concern. If 25-30% of plants show damage, examine field frequently. Treat at 2-3 active larvae/ft.
For more information on products registered for control of fall armyworm in Kansas, please consult the following 2024 K-State insect pest management guides:
• Wheat - https://bookstore.ksre.ksu.edu/pubs/wheat-insect-pest-management-2024_MF745.pdf
• Alfalfa - https://bookstore.ksre.ksu.edu/pubs/alfalfa-insect-pest-management-2024_MF809.PDF
Stacy Campbell is a Crop Production Extension agent in the Cottonwood District (which includes Barton and Ellis counties) for K-State Research and Extension. You can contact him by e-mail at [email protected] or by calling 785-628-9430.