By Jessica Domel
Multimedia Reporter

Recent rains may have provided much-needed moisture for most of the state, but they brought with them an unwanted pest—more armyworms.

Fall armyworms were already in some fields, but precipitation likely encouraged more outbreaks by creating favorable conditions for eggs and small larvae to thrive.

“We were getting calls last month around Crockett and Madisonville. We thought we had them under control, and now they’re back again with a vengeance. They’re even more wide-spread. If you pick an area, there’s probably armyworms,” Jared Klatt, location manager for Nutrien Ag Solutions in Caldwell, said in an interview with the Texas Farm Bureau (TFB) Radio Network.

Hay fields with a dense canopy and vigorous plant growth and irrigated fields are more susceptible to armyworm infestations, according to Allen Knutson, Texas A&M AgriLife Extension Service entomologist.

“Right now we’re mainly finding them in improved coastal, improved hay fields or Bermuda of some sort. We’ve had calls of some in Bahia grass fields. They’re also in pastureland,” Klatt, who is also president of the Brazos County Farm Bureau board of directors, said.

Normally, armyworms attack hay fields first because the grass is more tender and palatable. They prefer tender, lush, green areas.

“With these last bit of rains we’ve had over the past few weeks across the whole eastern side of the state, the armyworms are pretty much in pasture and rangeland also,” Klatt said.

He encourages growers to check their fields frequently for armyworms because the larger they get, the more they eat and reproduce.

“It doesn’t take long for them to totally wipe a field out. They’ll eat it to the ground,” Klatt said.

On a cloudy day, in the early morning or late evening, armyworms are typically in a crop canopy.

When it’s hot, they tend to hide under loose soil and fallen leaves.

According to Knutson, the larvae will chew the green layer from leaves and create what looks like a window pane. Later on, they’ll eat, or notch, the edges of leaves.

“They’re just eating a lot of forage, and a lot of people don’t have enough hay made for the year. So they’re having to do everything they can to save every bit of grass they can for their cattle,” Klatt said.

Growers should inspect their fields frequently to prevent widespread damage.

According to Knutson’s report, once larvae are three-quarters of an inch long or longer, the amount they can destroy increases dramatically.

“If they’re already big enough to where you’re seeing them crawling around, they’ve already done a lot of damage. You’re in rescue treatment at that point,” Klatt said.

During the last two to three days of feeding, armyworms can eat 80 percent of the total amount of foliage they consumed during their entire development.

Female armyworms can produce up to 2,000 eggs per cycle and create four to five generations per year.

There are several products approved for use this year to control armyworms. Some are restricted use and others are for general use. Some also have haying or grazing restrictions.

“You just have to check the label on what best fits the practice,” Klatt said. “That being said, certain products have longer residual than other things. So the price might be higher up front initially, but it lasts longer. We’re having a lot of failures on pyrethroids in the marketplace not working on worms—especially as the worms get larger.”

Restricted use products labeled for fall armyworms in pasture, grasses and hay include: Baythroid, Besiege, Tombstone, Dimilin 2L, Declare, Warrior II, Karate, Lambda-cyhalothrin and Mustang Maxx.

General use products include: Sevin 4F, Sevin80S, Carbaryl 4L, Sevin XLR Plus, Prevathon, Coragen, Malathion 57EC and Intrepid 2F.

“As (armyworms) get older and larger out there, a lot of the pyrethroids are failing. They’re just not working like they used to,” Klatt warned. “The other higher-dollar insecticides that are out there are working better, and they’re lasting longer, but it’s the upfront price that people kind of balk at it at first. Then they realize, ‘If I had to spray the other stuff two or three times, then it might be worth it to do this once, and I won’t have to come back again.’”

A chart with each insecticide, the pre-grazing interval requirements and pre-harvest interval for haying is available on page two of this document.