Like the children’s story of “The Very Hungry Caterpillar,” fall armyworms can munch their way through an entire field in short order if undetected.
Unfortunately, fall armyworms aren’t just a pest of fall. They can survive year-around in southern U.S. climates, and their moths fly north as temperatures warm in the spring. They complete a life cycle (egg-larva-pupa-adult moth) about every 30 days, according to Iowa State University Field Agronomist Virgil Schmitt. It’s in the larval stage where damage occurs, as the worms thrive on tender foliage of corn, alfalfa, pasture grasses, rye, wheat, and triticale.
Spring cover crops are a haven for armyworms. They may infest the next crop (example: corn planted into rye cover) or move to adjacent fields when the cover crop is harvested, according to Ohio State University agronomists Kelley Tilmon and Andy Michel. Migrating armyworms can reduce fields to sticks and stubble in a matter of days, and have even been known to take out lawns.
Scouting can help you stay ahead of armyworms, and should be performed at sunrise or sunset because they tend to be nocturnal, according to Schmitt. During the day, they will curl up in the residue at the base of the plant or the whorl of a corn plant and be harder to detect. This document from Pioneer Agronomy Sciences provides scouting tips for corn, and helps differentiate fall armyworms from other pests.
Corn crops most at risk are those in the southern U.S. and Texas; late-planted fields, fields with reduced tillage, late-maturing hybrids, and non-Bt hybrids without lepidoptera control.
Many foliar insecticides are labeled for armyworms. If scouting thresholds indicate treatment is warranted and you do spray, be sure to follow pre-harvest intervals listed on the insecticide label.
Schmitt said the larvae are more easily killed when they are small (3/4-inch or less in length), and it makes the most economic sense to spray at this stage. As they become larger, they are harder to kill and also near the end of their feeding cycle, and will stop feeding and pupate in a few days. After that, they will turn into moths and fly away to lay eggs somewhere else. A killing frost also will destroy the population.
For more on crops, read:
- How This One Technology Helped a Michigan Farmer Cut His Herbicide Use by 60%
- How Important Are This Year’s Planting Delays?
- A Tale Of Two Crops: Farmers Struggle Against Flooding And Drought
