Army Worms Are Marching!

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Last year, Caldwell County and the entire east coast learned how damaging fall armyworms can be in lawns and hayfields. The fall armyworm is a tropical cutworm that feeds on several grass species. For this pest to be a problem in Caldwell County, adult moths have to be carried here by hurricanes or tropical storms from southern Florida. This pest does not survive the winter in Caldwell County.

Since damage was so unexpected and extensive last year, NC State Extension setup 11 monitoring sites across the State for fall armyworms. If adult moths are detected on the traps, alerts are sent to landscapers, turf managers, farmers, or anyone that has signed up for pest alerts at turffiles.ncsu.edu.

Normally, fall armyworms are not a problem in Caldwell County. Prior to last year, I have only seen damage to one yard in 2017 and to a newly seeded site in 2015. However, last year (2021), hundreds of lawns and several hayfields were severely damaged by this pest. Some lawns had to be reseeded because the tall fescue was killed. The fall armyworm monitoring system will provide an early warning so landscapers and farmers can better manage this pest.

Fall armyworms are approximately 1-1½ inches long, and can vary in color from a green to mottled brown to almost black. Fall armyworms have a wide black stripe running down each side of the body. They also have a very distinctive upside-down “Y” marking on the head capsule.

The inverted "Y" on the fall armyworm head capsule is unique to this pest. (credit: Seth Nagy)

The inverted “Y” on the fall armyworm head capsule is unique to this pest. (credit: Seth Nagy)

This pest has a very wide host range but generally prefers grass, including coastal bermudagrass, fescue, ryegrass, bluegrass, Johnsongrass, timothy, corn, sorghum, Sudangrass, and small grain crops.

Fall armyworms that arrive in Caldwell County have overwintered in Florida. They migrate northward in the spring and summer, with each generation hopscotching northward. Female moths are carried north by winds and will lay as many as 1,000 eggs. These eggs hatch in 2-10 days into caterpillars. In large populations, fall armyworms can consume all the foliar tissue available and crawl in “armies”, devouring crops or turf stands. After the larvae feed for 2-3 weeks, they dig into the soil, pupate, and emerge as adult moths ready to lay eggs that will start the next generation.

Fall armyworm damage in turfgrass is very distinctive. Since armyworms cross the turf surface as a group, they create a noticeable line between damaged and undamaged turfgrass. Although fall armyworms do not have many specific preferences, newly-installed sod is more attractive and more susceptible to damage.

Fall armyworms can be more difficult to control than other caterpillar pests (true armyworms, black cutworms). When possible, mow and lightly irrigate the turf prior to treating. Insecticides are generally ineffective against large larvae (caterpillars), so be sure to note the size of the armyworms before making an application. Large larvae are likely to finish feeding and burrow into the soil to pupate, so only treat if larvae are relatively small.

Pyrethroids (particularly lambda-cyhalothrin), carbamates (carbaryl), and chlorantraniliprole will provide somewhat effective control against smaller larvae. For specific control information, check the https://www.turffiles.ncsu.edu/ website or contact us at the Caldwell Extension Center (828-757-1290).

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— Seth Nagy is the Caldwell County Cooperative Extension director. The N.C. Cooperative Extension. Caldwell County Center, 120 Hospital Ave., #1 in Lenoir, provides access to resources of N.C. State University and N.C. A&T State University through educational programs and publications.