Growings On: Look for fall armyworms often

Roger Gates

Complaints from homeowners about “dying grass” and “worms in the yard and on walls” have arrived with increasing frequency during the past several weeks.

At the same time, farmers are identifying damage resulting from fall armyworms in pastures and hayfields. The same pest that causes losses to farmers is creating a nuisance for homeowners.

Armyworm moths are ubiquitous and do not distinguish rural from urban areas. Armyworms are likely to occur anywhere in Georgia. University of Georgia Extension Entomologist Will Hudson describes fall armyworms as the “larval or caterpillar stage of a nondescript, small gray moth which overwinters in Florida and the tropics.”

Moths move north from Florida each spring and summer on weather fronts, spreading from south to north until the entire state is reinfested. This process takes several generations of moths, which is why worms usually appear in late summer and early fall in northern parts of the state.

An armyworm moth can lay eggs in batches of a few dozen to several hundred eggs, allowing populations to grow rapidly throughout the summer. These eggs hatch after a few days, and the caterpillars feed and grow for two to three weeks before pupating. About a week later the new adult moth emerges to start the cycle again. In summer, the complete cycle takes about four weeks, with 14-17 days spent as caterpillars feeding on vegetation.

Armyworm caterpillars feed on turfgrasses above the ground, primarily eating foliage and tender stems. When they are small, they don’t eat much, but when they molt to the last stage, they can eat up an entire pasture in four to five days. Fall armyworms feed on bermudagrass and other turfgrass species. Damage to established turf is most often aesthetic, but newly planted sod or sprigs can be severely damaged or even killed by fall armyworm feeding.

Newly hatched fall armyworms are white, yellow or light green, but darken as they mature. Mature fall armyworms are about 1.5 inches in length with a body color that ranges from green to brown or black. They have been described as having a greasy or oily appearance and are distinguished by the prominent inverted white “y” on their head capsule.

Small larvae easily go unnoticed. They do not eat through the leaf tissue; rather, they scrape off all of the green tissue and leave a clear membrane that gives the leaf a lacey or a skeletonized appearance. On the other hand, large larvae can quickly denude a turf or forage canopy.

Targeting smaller caterpillars of a half-inch or less is important for two reasons. First, the caterpillars do not cause severe damage until they reach a size of one inch in length. Second, as with many pests, smaller larvae are much more susceptible to insecticide control than larger ones.

You don’t want to treat a lawn or a field if it is not needed, but homeowners and landowners need to be scouting for the presence of fall armyworms regularly and frequently. It is important to catch an infestation before the armyworms cause major damage, and the bigger they are, the more damage they cause.

Scouting options for homeowners include close examination of the turf, possibly in tandem with the use of a soapy water flush. When you pour soapy water over a patch of grass (a half ounce of dishwashing soap/gallon water), the solution will irritate the larvae, which will drive them up from the soil surface very quickly.

Heavily-infested turf will also have visible greenish-black fecal pellets, or “frass,” on the soil surface. Other indicators of armyworm infestations may include high numbers of birds or even paper wasps that use the fall armyworms as food.

Armyworms rarely kill grass, but some lawns may be severely weakened. Feeding damage, coupled with an already stressed lawn, may justify applying insecticides. A number of effective products are relatively inexpensive. Others are more expensive but offer better control of larger worms, and a few give long-term protection although at a premium price.

Insecticides such as pyrethroids, such as bifenthrin, permethrin, resmethrin (usually ending with “thrin”) are effective to control the larvae. Bermudagrass lawns will usually recover within three to four weeks after infestation.

Insect growth regulators (IGR) are also available for use on turfgrass. They provide a different approach to insect control. Some are active only on caterpillars, while others are more broad-spectrum and affect a range of different insects.

The IGRs stop development of immature insects so they cannot grow and turn into adults. Many are absorbed into the grass and remain active but do not move into new growth.

Roger Gates is the agricultural and natural resources agent for University of Georgia Extension, Whitfield County. Contact him at

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