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home articles Pastures & Forages |

Texas forage producers should beware of fall armyworms

published: September 6th 2019
by: Adam Russell
source: Texas AgriLife Today


OVERTON – Texas hay and forage producers should be prepared to protect their pastures from fall armyworms, according to a Texas A&M AgriLife Extension Service expert.

In large numbers, fall armyworms can be devastating to hayfields and pastures due to their appetite for green grass crops. (Texas A&M AgriLife Extension photo by Dr. Bart Drees)

Vanessa Corriher-Olson, Ph.D., AgriLife Extension forage specialist, Overton, said 2019 has been a good year for hay production, but unchecked armyworms can still destroy a last cutting, stockpiled forages meant for fall and winter grazing, or young winter pastures, including ryegrass.

“It’s been very dry for a while now, so I would anticipate armyworms to emerge in destructive numbers following any significant rainfall,” she said. “It’s important for producers to be prepared at this time of year as we move into fall, which is when we see population increases of armyworms.”

Corriher-Olson said it is critical that producers have pesticides ready for applications as soon as armyworm numbers near three or more armyworms per square foot. Armyworms in those numbers should be treated immediately. Armyworms in the last two or three days of their larval stage consume 85% of their diet.

Corriher-Olson said armyworms will continue to be a threat to forages until the first freeze.

“Diligent scouting is important if you want to preserve a last cutting or stockpiled forages meant for winter,” she said. “But producers should also be mindful that armyworms will feed on winter forages like small grains and ryegrass. They prefer high-quality forages, so going into fall they will choose seedlings over Bermuda grass.”

Pest and path of destruction

Armyworm moths can lay up to 2,000 eggs that hatch in two to three days, according to a 2018 report by Allen Knutson, Ph.D., AgriLife Extension entomologist, Dallas. There are four to five generations per year.

Corriher-Olson said armyworm caterpillars are picky eaters that prefer high-quality, fertilized forage typically found on fields maintained for hay production. They are a common pest of Bermuda grass, sorghum, corn, wheat, rye grass and many other crops in north and central Texas.

Producers should scout each morning for armyworms, she said. Armyworms are night feeders and try to avoid daytime temperatures.

Armyworms are green, brown or black in color and can be identified by the white inverted Y on their head. They can grow up to 1 inch in length when mature.

The pest got its name because they appear to march across hay fields, consuming the grass in their path.

Corriher-Olson recommends insecticides labeled for armyworm control in pastures and hayfields. She said applicators should always follow all label instructions on pesticide use and restrictions.

Fast action

Fast action is paramount when it comes to reducing armyworm damage, so pesticides should be on hand, she said. Producers can save unused pesticides for armyworm or grasshopper problems in 2020 with proper storage of chemicals.  

“You don’t need to wait a day if their numbers are at threshold,” she said. “They are going to do a lot of damage quickly. If you find them in the morning, spray that day.”

AgriLife Extension has a number of resources with more information about armyworms, including AgriLife Extension Bookstore and Forage Fax.

Corriher-Olson said new and seasoned forage producers have been on edge regarding armyworms since last year when outbreaks were widespread and impacted production during a poor forage and hay season. She said producers shouldn’t fear the pest but should be vigilant if they want to defend their pastures.

“A lot of people were worried last year because armyworm populations exploded,” she said. “There was panic among producers, but did that panic turn into preparedness for this season? I don’t know.”

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