'Unprecedented' outbreak of armyworms are destroying lawns across the US, often overnight

Experts say a particularly widespread and intense outbreak of armyworms is overtaking lawns, leaving masses of Styrofoam ball-like eggs stuck to patio furniture and the sides of houses. But when they hatch, the pests can turn a lush green lawn into a brown, barren wasteland seemingly overnight.

"This year is like a perfect storm," said Rick Brandenburg, an entomologist at North Carolina State University. "In my 40 years, I have never seen the problem as widespread as it is this year."

Brandenburg said armyworms — more specifically fall armyworms — are laying siege to North Carolina but also as far west as Texas and as far north as Michigan and northeastern states, areas that rarely see such significant armyworm populations.

Eric Rebek, an Oklahoma State University entomology professor, said his phone has been ringing "off the hook" with requests for information about the infestation of grass pastures, lawns and fields of peanuts, alfalfa, cotton, double cropped soybean and sorghum.

He said the buggy brigade returns to Oklahoma each year in late summer and early fall, marching in large swaths from one food source to another until the winter frost kills them. But this year, he said there's been an "unprecedented" number of armyworms, not just in Oklahoma but also in Maryland, Kentucky, Tennessee, Oklahoma, Texas.

"They can easily munch their way through whatever, whether it's a lawn or a park or a golf course," Rebek said. "They just lay waste to everything in their path, moving through just like an army on the move."

In northeast Oklahoma, Kevin Walker, noticed the small caterpillars inundating his yard last month. While he was at Home Depot buying pesticide, he said every single person in line in front of him was also trying to expel the creatures from their own yards.

Walker said he was able to save most of the yard of his one-acre home, but some of his neighbors weren't as lucky.

“He said it was like overnight," Walker said of his neighbor. "...They had gone through it in that whole night ... That's why they call them armyworms."

What exactly is a fall armyworm?

Rebek said there are two kinds of armyworms: the true armyworm and the fall armyworm, the latter of which is the scourge homeowners are now facing. The fall armyworms, which are indigenous to the U.S., are the larval stage of the fall armyworm moth.

The caterpillars grow up to two inches long and can be green, brown or black in color. They can be identified by an inverted white "y" on their head capsules, Rebek said.

The fall armyworm also has two strains: the corn and rice strain, he said. The corn strain feeds on corn, sorghum and cotton while the rice strains eats rice, alfalfa and millet, as well as the pasture grasses and lawns.

What kind of damage can they do?

Fall armyworms feast on grass of all kinds, but the extent of the damage depends on the type of grass, Rebek said. Warm season grasses grown in southern states can regenerate after armyworm invasions, but the caterpillars can permanently devastate cool season grasses.

"For warm season grass, is mostly an aesthetic issue," he said. "But if you have cool season grass, you probably want to treat your lawn."

Why are we seeing such a widespread, intense outbreak?

Experts say it could be a number of factors, including a warming climate, wetter weather or changes in natural enemies such as predators, parasites and pathogens.

"It's likely a very complex interaction that is occurring this year that leads to this outbreak," Rebek said, adding that it's common for populations to ebb and flow. "It's hard to point your finger at any one thing."

Brandenburg said while climate change has the potential to increase the likelihood of tropical pests like fall armyworms infesting lawns, it's difficult to make a direct link between the two because so many factors are at play.

How did the armyworms get here?

Unable to survive in freezing temperatures, the fall armyworm spends the winter in the Gulf Coast states before heading north on southerly winds, Brandenburg said.

He said the creatures begin to appear in spring in southeastern states before showing up in the Mid-Atlantic by mid-summer and the upper Midwest and northeast by late summer. They can be almost annual pests in southeastern parts of the country and sporadic pests of once every decade or so in eastern states.

Brandenburg added fall armyworms have recently invaded some areas of Sub-Saharan Africa, where it infested corn, maize, sorghum and millet crops in 2016 before spreading through Yemen and South Asia to Thailand and China.

Rebek said this movement was likely done with the help of people, who may have transported armyworms to other countries through trade.

How do you prevent armyworm attacks and revive your lawn post-siege?

Unfortunately, there's not much people can do to protect their lawns from the scourge.

"It's hard to deter them," Rebek said. "And it's hard to predict where they'll land and prevent that from happening."

Rebek warned homeowners to be watchful, saying "It really just comes down to monitoring and being vigilant and watching for signs of trouble."

Pratt, from the University of Kentucky's Cooperative Extension Service, said once you notice a patch of brown grass, you're probably too late. Since the armyworms have likely already burrowed beneath the surface to begin pupating, she suggested waiting to re-seed your grass until the second wave begins. She said to watch for the next round of egg masses to appear and then treat your yard with insecticides for small caterpillars.

"You're going to plan on managing them and not controlling," Pratt said. "Nothing will ever do 100% control unless you're also getting rid of your lawn."

She added dumping a jug of soapy water onto the eaten grass can push buried armyworms to the surface where they can be seen.

Brandenburg said one of the first signs to watch for is birds feeding on the caterpillars. If you see a large number of birds in your yard, they may have found a significant food source like a battalion of armyworms.

Rebek advised that people to check the label on their insecticide because many are broad spectrum and kill more than just fall armyworms. These insecticides can kill predatory insects that help control other pest insects, pollinators like bees, and Monarch butterflies.

He added people should find solace in the fact that the cold will end the scourge of the armyworm.

“When we get our first killing frost, there will be no further action that will be necessary because that cold weather will ultimately kill them off, and then, you know, we'll wait and see what happens next year,” Rebek said.