by Dr. Deidre Harmon & Dan Wells

By DR. DEIDRE HARMON & DAN WELLS N.C. State University

Now is the Time to Scout for Fall Armyworms

We are entering the time of year when we are starting to think about fall stockpile, new plantings of cool season forages, and the dreaded fall armyworm pressure. Fall armyworms are a reoccurring problem in the Southeast, and the pests feast on hayfields, pastures, and even well groomed lawns. Although we often see them in the coastal and piedmont regions, it is less common to see them at higher elevations. However, in 2021, we had reports of severe armyworm damage from all across North Carolina, from the coast to the mountains. They feed on a variety of forage species, including pearl millet, sorghumsudangrass, bermudagrass, crabgrass, alfalfa, and tall fescue. Persistent scouting and rapid treatment of infected areas are key to saving pastures and hay crops in areas where fall armyworms have been reported.

So why are armyworms worse in some years and can infect areas that normally do not have issues? Some entomologists suggest that the persistent rainfall in most of the Southeast in 2021 produced an abundance of vegetative forage growth, which is the ideal environment for the worms to thrive in. In these conditions, worms can appear to consume an entire field overnight, turning green, lush forage into a desolate field of brown dust. At first glance of infected fields, it may appear that a pasture looks droughty or overgrazed. The grass is starting to turn brown and is noticeably shorter as if animals were only grazing in one spot. If this sounds like a familiar scene, it is time to immediately go scout for fall armyworms. It is best to scout for armyworms during the cooler parts of the day when they are more likely to be consuming a meal of forage. During the hotter parts of the day, you may find the caterpillars taking refuge from the heat at the base of the plant, in the whirl of some forage species (sorghums), or on the ground and underneath any leaf litter that may be on the soil surface. When

Pasture infected by fall armyworms with a patchy, overgrazed appearance. Population density of five armyworms per ft2 .

Pasture infected by fall armyworms appears to be droughty and overgrazed.

scouting fields, take note of how many armyworms are found within a square foot area. Typically, the threshold is around three armyworms per ft2, so if you are at or exceed that threshold, it is time to think about utilizing a control option.

When choosing a chemical control, it is important to note that some chemicals are insect growth regulators, meaning they disrupt the life cycle of the worm, and some are pyrethroids, meaning they will immediately kill some of the caterpillars. It is also important to recognize that some of the chemicals only target a certain age of armyworm, also called instars. Some have longer residual controls, some are more rainfast, meaning they will still be effective even after short bouts of rainfall, and some have grazing and hay restrictions. Scouting fields and identifying what stage(s) of armyworms are present in the field is important in helping decide which control strategy or even multiple chemical control strategies will work best.

Lastly, getting a good handle on fall armyworms requires persistence and attention to detail. Frequent scouting is required to make sure chemical measures control populations and reinfestations do not occur. Additionally, as we move into the time of year where winter annuals and fescue and orchardgrass stands are trying to be established, it is more important than ever to scout. Newly established fields of grass can be easily and completely killed by an uncontrolled population of fall armyworms. So it looks like we will be out scouting until at least our first big frost.

The following list of insecticides was compiled by Dan Wells, Johnston County Livestock Extension Agent, and can be found at https://forages.ces.ncsu.edu/wpcontent/uploads/2020/08/FAW-ControlProducts.pdf?fwd=no.

Please note that many of these products may not be available in your local area. There are reports of limited availability of some products.

Armyworms hiding in leaf litter during the middle of the day in a stand of sorghumsudangrass.

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