As one of our Extension Entomologist recently said, we might end up remembering 2021 as the “Year of the Armyworm.” There have been many reports across the Midwest of large fall armyworm populations damaging crops, lawns and turf. There were some reports of true armyworms also.
There are true armyworms, fall armyworms and army cutworms. In our area it appears as though the fall armyworms are the main culprits, or the highest in numbers. There are confirmed reports of early planted wheat for grazing that has been mowed completely down/eaten by armyworms, and volunteer wheat as well. Once they have eaten all the wheat in the field they are eating on anything else green in the field such as weeds.
As per the name armyworms they can march across fields or landscapes in large numbers. How far can they travel? Well no one knows but they can move to find new food. The fall armyworm migrates into Kansas each year from southern states, arriving in July where it deposits eggs on corn, sorghum and other summer crops. They do not over-winter in Kansas. Spraying to kill the armyworms before planting your wheat is not advised, but delayed planting is advisable and once you have planted, keep a close watch on it.
There are several generations of armyworms during the growing season. As the day-length is getting shorter and nights cooler, the emerging moths should migrate south. But some larvae/caterpillars are still very small and can feed for roughly another 10-14 days. There might even be another generation or suicide generation of armyworms?? This year it may take a hard frost or freeze to stop them.
True armyworms infest primarily grasses (sorghum, corn, brome pastures, lawns, etc.) and often this time of year, wheat, but occasionally alfalfa. Fall armyworms have a little wider host range which includes alfalfa, soybeans, corn, sorghum, and wheat.
The color of these caterpillars is highly variable; the dark color depends on melanin deposition, which can increase at low temperatures, and the intensity of bright colors depends on plant pigments obtained in the diet.
Young fall armyworms are 1/2 to 3/4-inch-long, and are 1 ½ inches long at maturity. Body color may vary from green to almost black, but light stripes will be visible along the length of the body. Look for a whitish inverted “Y” on the face. It normally takes 2 to 3 weeks to develop from egg to pupa. The adult is a moth.
True armyworm larvae are 1½ to 2 inches long at maturity. The head capsules have honeycomb-like markings, and the body lacks obvious hairs. Overall body coloration varies, but is usually some shade of greenish-black with two alternating dark and orange stripes running lengthwise down each side plus a light or faint white line on the back.
Regardless of which armyworm it is, if you find any in newly planted wheat or fall planted alfalfa, monitor it closely. For recommendations of spraying thresholds, you can google Wheat Insect Pest Management, KSU or Alfalfa Insect Pest Management, KSU. Or go to our web site at www.cottonwood.ksu.edu and click onto Crops and Livestock.
If you have any questions, please do not hesitate to give me a call at the Hays Office 785-628-9430.
Stacy Campbell is an Agriculture and Natural Resources agent for Cottonwood Extension District. Email him at firstname.lastname@example.org or call the Hays office, 785-628-9430.