March of the Armyworms

The fall armyworm, Spodoptera frugiperda, eats foliage of many different kinds of plants, such as turfgrass, shrubs, and agricultural crops. Several reports of these armyworms have been seen in large populations as they march in and feed both day and night, causing circular or irregular deadened patches of turfgrass. Armyworms do not usually kill lawns, especially bermudagrass lawns, but will scalp them; however, St. Augustine lawns are more susceptible, and can be completely lost after armyworms feed.
Armyworms have four life stages: egg, larva, pupa and adult. The eggs are very small, and are laid on leaves at night. The larvae hatch from the eggs and feed mostly at night. They tend to hide in thatch and debris in the daytime. The young larvae are white with black heads but develop a prominent white line forming an inverted “Y,” with stripes along the body as it matures. The larvae will become 2 inches in length before entering the soil to pupate. Then the adult moths emerge, mate and lay eggs. The adult moth has a wingspan of 1 ½ inches, with silver-white hindwings and dark grey front wings with light and dark splotches.
The locations of large populations of armyworms vary each year throughout the state. However warm, humid climates, along with large amounts of thatch are favorable conditions for fall armyworms to multiply. Armyworms should be controlled when they occur in large numbers or plant damage becomes excessive.

Some Control Options:

Some Non-Chemical Control Options:
Eliminate thatch to reduce develop sites of the armyworms. Also monitor for sites of infestation in the turfgrass by flushing the area with soapy water if damage is seen but the armyworms are not seen. This will cause caterpillars to move around within minutes so they can be spotted.

Some Chemical Control Options: Armyworms can be controlled using such insecticides containing the active ingredients permethrin, cyfluthrin, bifenthrin or esfenvalerate. Spot treatments or whole lawn treatments can be effective, depending on the size of the population.

Photo of fall armyworm. Photo by Bart Drees, Professor and Extension Entomologist, Texas A&M University.