This article was written by Dr. Tom A. Royer, Extension Entomologist.
I have received two reports of army cutworms infesting wheat and one report of them infesting canola.
Army cutworms overwinter in Oklahoma. They tolerate cold temperatures and feed throughout the winter months. Adult army cutworm moths migrate to Oklahoma each fall from their summer residence in the Rocky Mountains. They usually seek bare or sparsely vegetated fields (like a newly prepared field ready for sowing wheat, or a field that was “dusted in” but not yet emerged). Just because army cutworm moths prefer to deposit eggs in bare soil, it doesn’t mean that no-till fields with residue are safe from infestations; so ALL wheat fields need to be scouted.
Moths lay eggs from August through October that hatch soon after being deposited. This explains why a producer often sees different sizes of larvae in a field. Army cutworms feed throughout the winter and molt seven times before they turn into pupae in the soil. Most larvae will be gone by late March, and adult moths begin emerging in April and fly back to the Rocky Mountains to spend the summer.
Army cutworm damage in a wheat field
Army cutworms can cause severe stand loss of wheat and canola if not controlled. Cutworm damage often goes unnoticed through the winter because the caterpillars grow slowly and don’t get big enough to cause noticeable damage until temperatures warm in the spring. Unfortunately, if wheat is not growing rapidly because poor growing conditions due to drought (which cutworms also like), they can be even more devastating.
So it becomes important to check the fields for cutworms. If you notice a field at this time of year with a numbers of starlings or black birds feeding in a concentrated area of your wheat field, they are likely feasting on army cutworms!
Close up of an army cutworm larva
All wheat fields need to be scouted NOW. Sample a field by stirring or digging the soil to a depth of two inches at five or more locations. Also, turn over those dried up cow patties, as they are a favorite hiding place for army cutworms. The cutworms will be “greenish grey”, and will probably curl up into a tight “C” when disturbed. A suggested treatment threshold is 2-3 caterpillars per foot of row when conditions are dry or 4-5 caterpillars per row-foot in fields with adequate moisture.
Control suggestions are listed in Current Report-7194 Management of Insect and Mite Pests in Small Grains or E-832, the 2015 OSU Extension Agents’ Handbook of Insect, Plant Disease, and Weed Control.
Army cutworms are also a potential pest of canola. Scout fields just as you would in wheat. The suggested treatment threshold for cutworms in canola is 1-2 per row-foot. Current recommendations for control of army cutworms in canola are listed in CR-7667, Management of Insect and Mite Pests in Canola: http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-3045/CR-7667web2017.pdf.