The armyworm is marching across the Midwest. When will it stop killing the grass?

Alice Mannette
The Hutchinson News
Fall armyworms crawl across the grass.

Armyworms are on the march in Kansas.

Although they are quite small, this tiny worm can cause quite a bit of damage.

This year, they are heading into wheat fields and marching over grass blades.

"They are kind of cyclical.. some years you don’t have that many, some years you’ve had a lot," said Cassie Homan a horticultural agent at Post Rock District of Kansas State Extension. "This year it's been crazy. They’re all over the sidewalks."

The manager of Stutzmans Greenhouse & Garden Centers, Jason French, said this is the largest amount of armyworms he has seen in about eight years.

"There was quite an infestation," he said. "A few weeks ago, it was pretty severe."

What do armyworms eat?

Armyworms are out in droves across the Midwest. Although these tiny creatures love a good leaf or blade of grass, they can be discriminating, preferring fescue and bluegrass above other flora. 

They'll also head into cornfields, but they leave the kernel alone. As for wheat, Homan recommends planting the crop after these little worms head south down to Texas for warmer temperatures.

Armyworms invade fields or landscapes as large groups and can cause a lawn to turn brown overnight, sometimes munching grass down to the soil.

"They can do quite a lot of damage to the lawn," French said. "We've had a lot of people have to reseed."

Feeding occurs late at night and in the early morning hours.

"Normally, armyworm damage does not kill established turf but may if populations are high enough," Homan said.

Who are these armyworms?

The Fall Armyworm is in its larval stage from 14 to 22 days.

Young worms are ½ to 3/4 inch long. Mature ones can reach up to 1 ½ inches long. Although they range in color from green to almost black, they always have a light strip along the length of its body, with a whitish inverted “Y” on the top of the worm's black head.

Homan said each worm takes two to three weeks to progress from egg to pupa. The adult is a brown moth and usually flies at night.

Although treatments work earlier in the year, Homan said, this late in the season one should simply water and wait for them to vacate. But, if the infestation is excessive, French recommends treating them with good granular insecticide, applying the chemicals in late afternoon and watering the granules in. 

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"Everything just came together this year," French said. "The weather conditions were just right (for the infestation of armyworms)."

Hamon said these worms are good for the birds, but this year, there are too many of them. 

"They're kind of wreaking havoc this year and people are paying attention," Hamon said. "People are curious because of the sheer numbers of them."