From drought and extreme heat to insect infestation, a farmer’s problems never seem to cease. Fall armyworms can be a farmer’s worse nightmare as they feed on pasture forage, corn, cotton, beans, and numerous other plant species. Dry hot summers typically create favorable conditions for armyworm infestations. Armyworms can wreak havoc on bermudagrass and Bahia grass fields. Intense infestations have been known to eat through large bales of hay, destroying them so severely that they fall apart.

Armyworms may be seen on foliage any time during the day; however, your best chances to observe these insects are early in the morning and late in the evening. Droppings from the caterpillars can be seen on the ground with heavy infestations. They also tend to gather in the leaf litter.

Adult fall armyworms are 1.5 inches long. Fall Armyworms always have striped bodies, but they are not always the same color. Their background color ranges from light green to almost black. Identification of Fall Armyworms is by four black dots on the back of the tip of the abdomen. Larger caterpillars usually have a light-colored, upside-down Y-shape on the head and three white lines on top of the segment just behind the head.

Before any control measures are taken, producers should first scout their fields to determine the extent of their infestations. Scouting consists of walking into your field from all four sides. Stop at various locations in the field and look closely for small caterpillars feeding on the grass and other foliage. If any are spotted, do your best to estimate the number of caterpillars per square foot in eight different sites. Divide the total worm count by eight to find the average number of armyworms per square foot. Take samples in the interior of the field because armyworms tend to be the heaviest at field margins. Often, only the field margins require to be treatment. Thresholds for pastures and lawns vary with conditions but typically control measures should be taken when worm counts exceed three or more worms per square foot. Pay attention to the size of the pests as this is important to the success level of treatment. Treatment should be considered while the worms are half an inch to one inch in length. Once they have matured to over one inch long, much of the crop damage has already taken place; therefore, chemical control will not likely provide economic return.

Refer to the latest publication of Louisiana Insect Pest Management Guide from LSU AgCenter for pesticide recommendations and Best Management Practices in controlling armyworms in grass pastures and hay fields at the following link:

2026 Louisiana Field Crops Insect Pest Management Guide - Pasture and Forages