Due For An Outbreak? Extension specialists want farmers to be on alert for army cutworms this year

Sam Waters | Fruita, Colo.
Army cutworms along a road on Glade Park in Mesa County, from the 2003 outbreak. (Photo courtesy of Bob Hammon, CSU Extension)

While the growing season is just starting to gear up for farmers and ranchers across Colorado, an army of antagonists might already have a jump on them.

That is, an army of cutworms.

This year could produce another major outbreak year for army cutworms, the caterpillar form of Miller Moths, Colorado State University extension agents said.

The last outbreak of army cutworms occurred in 2003.

“We’re about due for it,” said Bruce Bosley, an CSU extension agent for Logan and Morgan counties. “About every ten years we have a major army cutworm outbreak.

“It’s very hard for entomologists to predict what’s going to happen,” Bosley continued. “We’re just seeing quite a few cutworms out here in fields and certain areas. So what we say is just be on the lookout.”

Army cutworms, named so because they move in groups like an army, feed on broadleaf plants — like alfalfa, as well as wheat and different grasses. They begin feeding earlier than most other insects and are currently very active.

“The crops that are at risk right now are things in ground that should be greening up right now, like wheat and alfalfa,” Bob Hammon said.

Hammon, too, works as a CSU extension agent in Mesa County, specializing in agronomy and entomology.

So far he has heard of several reports of people finding army cutworms in large numbers statewide.

The native insect had ideal conditions this past year with plenty of moisture and milder winter conditions in some parts of the state that allowed more eggs to survive.

“They affect the whole state at different points in their life cycle,” Hammon said.

The cutworms will continue to feed until the end of April, at which point they will start turning into their adult form. Once they become Miller Moths, they will travel to higher, cooler elevations where they will spend the summer.

During their movement they may plague cities and be a large nuisance during the months of May and June. In the fall, the Miller Moths migrate back to lower elevations where they lay their eggs.

Army cutworms can get into fields and totally defoliate a crop before growers even realize they have them, unless they know what to look for. They also eat on native grasses and can wipe out large areas of feed on range lands.

Hammon recalled when the outbreak in 2003 caused grazing land in Unaweep Canyon in Mesa County to become completely bare of feed.

The extension agents recommend that growers go scout their fields for areas that look less green than the rest of the field. If the leaves looked damaged, growers should inspect the ground for cutworms.

Homeowners may also see the cutworms appearing in gardens and lawns.

Army cutworms work mainly at night and hide in the soil during the day. They can be found by digging down about three-quarters of an inch into the soil.

Bosley said to look for a grayish-green worm that has no hairs that curls into a round, C-like shape if touched.

The best way to prevent widespread damage would be to spray the affected crops with an insecticide label for cutworms. Affected range land may be more difficult and costly to manage with a pesticide, so ranchers should be aware that they may see some areas with less feed this year.

“As the value of the land and the value of the crops increase, the impact is greater,” Hammon said.

Higher moisture levels in the soil this year may keep the cutworms closer to the surface making them more susceptible to natural predators like birds and rodents, which may result in a more natural pest control.

But without some management, infested areas could see significant damage. ❖