Brown County livestock producers and landowners are being urged to inspect pastures, hayfields and newly established winter forages for fall armyworms as the fall growing season continues. The pests can cause major foliage loss in a short time, particularly after rainfall and mild temperatures create favorable conditions for population growth.
Anna Davenport, the Brown County Extension agent for agriculture and natural resources, said regular scouting is important for protecting forage investments. Fall armyworms are most common from midsummer through early November, but activity may continue until freezing temperatures end the growing season.
Why armyworms can damage forage quickly
Fall armyworms are caterpillars that may be green, brown or nearly black, with lighter stripes along their bodies. A pale, inverted “Y” marking on the head and four dark spots arranged in a square near the rear are identifying features.
Young caterpillars can be difficult to see, but their feeding accelerates as they mature. Armyworms consume about 80% of their total food intake during their final two to three days of feeding. As a result, a pasture that looks healthy one day can show substantial foliage loss soon afterward.
The insects commonly feed on bermudagrass, ryegrass, wheat and other forage grasses. Newly planted winter wheat and other small grains deserve particular attention because young plants have less foliage to withstand feeding.
Where and when to scout
Producers should walk pastures and hayfields regularly, especially after rainfall or irrigation. Recently fertilized fields with lush, actively growing forage may be especially attractive to armyworms.
Early morning, late evening and cool, cloudy conditions are the best times to look because the caterpillars are more likely to be feeding. During warmer parts of the day, they often move toward the soil surface and hide beneath plant debris.
Warning signs include small caterpillars, ragged leaf edges and grass blades with a thin, transparent appearance where young larvae have removed the green tissue. Checking multiple locations throughout a field, including areas away from field edges, can provide a more accurate picture of activity.
When treatment may be warranted
Finding a few armyworms does not automatically mean an insecticide application is needed. Treatment decisions should consider the number and size of caterpillars, the forage's growth stage and the crop's economic value.
Insecticide treatment may be appropriate when populations exceed two to three armyworms at least one-half inch long per square foot. Newly established small grains may require action at lower numbers because seedlings are more vulnerable.
When treatment is justified, applications generally work best while caterpillars are small. Producers should use only an insecticide labeled for the forage crop and follow directions covering application, grazing restrictions and hay harvest intervals.
Regular inspections can help Brown County producers protect winter grazing and remaining warm-season forage, support livestock nutrition and reduce reliance on purchased winter feed. For help identifying armyworms or evaluating management options, contact the Texas A&M AgriLife Extension Office in Brown County at (325) 646-0386, visit 605 Fisk Avenue in Brownwood, or email [email protected].