Duke Myers, owner of Duke’s Lawn Care in Wichita, KS, first became aware of armyworms in his service area when a friend sent him a picture about a week ago. Now, he can’t go to a customer’s home without being flagged down by a neighbor concerned for their lawn, reported the The Wichita Eagle newspaper on August 15. Meyers, who has been taking care of lawns in the Wichita area since 1997, told reporter Michael Stavola that he hasn’t seen armyworms this bad since 2000.
Armyworms are actually caterpillars that become moths. The name ‘armyworm’ originates from agriculture, where infestations sometimes resemble an army as they move across large agriculture fields. The same behavior can sometimes occur in turf, where areas as large as a football field can be consumed in the course of two to three days, according to an article in AggieTurf, from Texas A&M AgriLife Extension.
While there are different species of armyworm, the fall armyworm is the most common cause of damaged turfgrass. They feed primarily on bermudagrass, ryegrass, fescue, and bluegrass. Colored either green or muddy brown with a wide, horizontal black stripe running down each of their sides, fall armyworms measure about 1″ to 1.5″ in length and have a lightly colored upside-down “Y” on their head. They are usually found from July to October, and outbreaks may occur after heavy rainfalls. Since armyworm eggs can’t last through a cold winter, they are most often found in the southern U.S., where there can be as many as four or five generations per year.
Though armyworm damage may initially resemble drought stress, it will progress to complete loss of foliage if numbers are sufficient and turfgrass is left untreated. There may also sometimes be a distinct line between damaged and undamaged areas.
So what’s the best treatment? Here are a few tips:
- According to the Wichita Eagle, to test for armyworms, pour warm, soapy water on affected areas and wait a few minutes. The armyworms should come to the surface.
- Myer’s personal choice is liquid insecticide, which he said works “exponentially better than granular.” Spray the affected areas and surrounding grass in the evening or spray the whole lawn if you want to be thorough.
- The earlier the treatment, the better. Insecticides containing bifenthrin, acephate or chlorantraniliprole will work, according to Sod Solutions. For specific pesticide recommendations from Sod Solutions, visit here.
- Grass species selection matters. Healthy and actively growing bermudagrass typically recovers after infestation and defoliation due to its aggressive rhizomatous and stoloniferous growth habit. However, newly established bunch-type grasses, such as ryegrass or fescue, may be stunted or killed by armyworm feeding, according to AggieTurf.
- Avoid a turf monoculture. A previous Turf article reported on a study where mixing cultivars of St. Augustine was found to be less palatable to armyworms than a stand of one cultivar alone.
- Adult moth armyworms fly and mate at night, after which the female will lay up to 1,000 eggs in masses on host plants or indiscriminate surfaces such as bleachers, fences, light posts, or any erected structure in a lawn. Thus, the presence of lights around athletic fields, parks, and golf courses can increase the likelihood of moths being present near these turfgrass settings and should be considered when scouting for eggs of these pests, says AggieTurf. (Armyworm moths don’t lay eggs in the grass. The larvae drop down into the grass after hatching.)
If you have noticed a caterpillar that doesn’t resemble the fall armyworm’s description, check out Sod Solutions blog on sod webworms. Symptoms of a sod webworm invasion are very similar to those of fall armyworms.
Caterpillar Head Photo Credit: Steve L. Brown, University of Georgia, Bugwood.org; Moth Photo Credit: Lyle Buss, University of Florida, Bugwood.org; Egg Mass Photo Credit: John C. French Sr., Retired, Universities:Auburn, GA, Clemson and U of MO, Bugwood.org