Authors: Amber Starnes, Brian Beer, Lee Van Vlake, Dr. Liliane Silva
It is time for hay and livestock producers to consider the prevention and control of fall armyworms in pastures and hayfields. The fall armyworm, Spodoptera frugiperda, is known as a chronic pest in the Southeast region of the US. Climates in South Carolina and North Carolina favor their development due to hot, dry summers being typical. Generally, fall armyworms are most numerous in late summer and early fall, but in some years, they can start occurring in late June. The caterpillars feed on a variety of forage crops, such as bahiagrass, bermudagrass, pearl millet, and sorghum, but the most damage is usually seen in lush, green forage stands.
Fall armyworms are susceptible to cold, making late summer/early fall prime time for their development, which means this is also the prime time to prepare for the prevention and control of an invasion. Often, this pest is present but goes undetected because of the initial small size of the larvae. Mature caterpillars cause the most damage because of the vast amount of foliage they consume, and damage may often appear overnight. Damage varies in appearance and severity according to the length of time that the caterpillars were feeding, but also with some visual distinctions regarding the type of grass and management practices used. In a pasture situation where the grass has been overgrazed, the grass may seem to thin out and develop brown spots. All tender green material may be removed in hayfields, leaving only tough stems a few inches long. Established, healthy bermudagrass is rarely killed by a single infestation of armyworms. Still, the complete defoliation caused by severe infestation weakens plants and deprives livestock of pasture or a hay producer of hay cutting. Fall armyworm damage on newly established forages can be a more severe situation. The crops can be severely stunted or killed if fall armyworms feed too far down on these plants. Most commonly, fall armyworms forage during early morning and late afternoon, when temperatures cool down, making this the recommended time to scout the fields for the pest or signs of damage.
Scouting hayfields and pastures should begin in June. While scouting, the following descriptions are stages of the fall armyworm that you may notice. Fall armyworm eggs are creamy-white and dome-shaped with a flat base. Eggs are laid in clusters of 25 to 100, with a single adult female moth laying as many as 2,000 eggs on lower leaf blades. The egg clusters will have a hairy/fuzzy appearance. The newly hatched larvae are light green to cream-colored with a dark head capsule. The newly hatched larvae are tiny and often go unnoticed. As the larvae develop, they become darker with light-colored lines down the side of the body. The head capsule will be dark with a light-colored inverted Y marking on the front. Another identifying mark will be the four dots on the next-to-last abdominal segment. Once fully grown, the larva measures about 1 ½ inch long.
Large armyworms frequently disappear almost as suddenly as they appeared, either burrowing into the ground to pupate or migrating in search of food. The adult fall armyworm is an ash-gray moth with a 1 ½ inch wingspan. It will have whitish spots near the tip of the front wings, and the hind wings are whitish with narrow brownish wing edges. With the rapid rate of development of the fall armyworms during late summer/early fall, it is not uncommon to get 5 or more generations produced each year. Generations can overlap, but most of the fall armyworms in one area will be similar in life stage development, making damage seem to come in waves that follow the cyclic development of the fall armyworms. Some signs that indicate fall armyworms are cattle egrets and/or geese feeding in concentrated areas, foliage that has been chewed on the underside only, and forage that appears to be ‘frosted.’ Once damage becomes more severe, the field will have dead spots appear. It also pays to notice the condition of your neighboring fields, in that this pest will sometimes invade an area in search of food once an adjacent field has been defoliated.
Scouting pastures and hayfields can help detect fall armyworm infestation before it causes economic damage. If fields are already damaged from fall armyworms, these fields should be closely monitored to determine if control is necessary at that time and for the rest of the season. If a pasture or hayfield has been heavily damaged, fertilize as recommended to allow for growth to occur, whereas a severely damaged field may need to be rested.
If you detect fall armyworms, there are certain insecticides that are labeled for pastures and hayfields that can be used for treatment. The decision to control fall armyworms is determined by the threshold for control and the stage of the fall armyworms. A population of 2-3 or more fall armyworms per square foot is a reasonable treatment threshold. As with other pests, timing is essential. Apply insecticides early or late in the day because fall armyworm larvae are most active at these times. Below is a link with insecticides labeled for fall armyworms. As always, read the label before use to ensure proper precautions are taken, such as any grazing or haying restrictions, and to ensure the product will treat the intended target. Pay attention to the residual activity of the products labeled for use and prefer those with high residual activity. Remember that multiple generations of fall armyworms may be developing in an area simultaneously (adults, larvae, eggs), and their life cycle is about 3 weeks from hatching to pupating. A second insecticide application to the same field may be needed 7-10 days after it was first treated, depending on the level of infestation and the control achieved after the first application was conducted. Always evaluate the effectiveness of the first application control to determine if a second may be necessary; remember that, depending on the level of damage caused to the plants, it can compromise the plant’s ability to regrow and persist in a field.
For specific recommendations and further assistance, please contact your local Livestock and Forages. More information can be found at: https://www.clemson.edu/extension/agronomy/pestmanagement21/2021pmhpastureinsectcontrol.pdf
Sources:
Loftin, K., Lorenz, G., Corder, R. Managing armyworms in pastures and hayfields. FSA #7083. University of Arkansas Cooperative Extension. Accessed May 2025. Available at: https://www.uaex.uada.edu/publications/pdf/fsa-7083.pdf
Marshall, M. et al. 2021 South Carolina Pest Management Handbook. Clemson University Cooperative Extension.
