FALL ARMYWORM MANAGEMENT IN LAWNS

Picture courtesy of Florida Extension.

Tim Reed, Extension Entomologist
July 29, 2008

This is the time of year when home owners need to start checking their lawns for fall armyworms (FAW’s). Problems with FAW’s generally start in extreme south Alabama in late July to early August and then move quickly northward. FAW’s were especially bad last year along the Gulf Coast where some athletic fields required 4 insecticide treatments. FAW’s will eat many kinds of grass, especially bermudagrass that is well-fertilized and watered. Home owners frequently notice them shortly after their grass starts to thin. First let’s talk about the biology of this pest and then cover control options.

FAW’s are susceptible to cold, and are unable to survive even the mildest winters in Alabama. Each year, FAW moths, carried by air currents, make their way from Central and South America. The size and timing of the initial moth flights are two factors that influence the outbreak potential of this pest. FAW damage often seems to appear "overnight." Young armyworms don't eat much. Almost all the damage is caused by the oldest caterpillars which eat more than all the other ages put together. Larger fall armyworms will sometimes "march into" (quickly invade) an uninfested area in search of food once an adjacent field or lawn has been defoliated. Large armyworms frequently disappear almost as suddenly as they appeared, either burrowing into the ground to pupate or moving on in search of food.

The 4 stages of development of the FAW are the egg, larvae, pupae and adult. The adult is an ash-gray moth with a wing-span of about 1½ inches. The front wings are mottled and have white or light gray spots near the tips. The back wings are white with a narrow, smokybrown edge. Moths become active at twilight and feed on nectar. They have an average life span of 2 to 3 weeks. The female moths lay eggs at night in masses of up to several hundred in grass and on light-colored surfaces, such as fence rails, tree trunks, and the underside of tree limbs. The eggs are light gray and covered with grayish fuzz from the female's body. These masses darken with age, and the eggs hatch within 2 to 4 days. All the eggs within a mass hatch at about the same time.

The tiny, light-colored, black-headed larvae (caterpillars) spin down to the ground on silken webs and begin to feed. As they grow, their bodies darken and noticeable stripes appear. When fully grown, larvae may be up to 1½ inches long and vary in color from light green to almost black with several stripes along the body. The "face" is marked with a light colored inverted "Y." Development from egg to fully grown larva requires about 2 to 3 weeks. The larvae feed for two to three days, grow, form a new skin and shed the old one. Once the caterpillar reaches maximum size it burrows into the soil and forms a pupa. The moths emerge in about 10 to 14 days. Three generations can occur in south Alabama.
Homeowners should begin inspecting their lawns each week for FAW To check areas where FAW populations are suspected, use soap flushes (about 2 tablespoons of lemon-scented dishwashing detergent in 1 gallon of water) to bring larvae to the top of the sod. Since other insects (such as grubs, mole crickets, sod webworms) may be involved, the soap flush allows you to check for these and other soil insects. There are several approved insecticides available to homeowners that provide effective control of FAW. These include labeled products containing carbaryl, trichlofon, Bacillus thuringiensis, and several pyrethroid insecticides. A number of pyrethroid materials are available in a variety of homeowner formulations for use as broad-spectrum contact insecticides. Common pyrethroids include bifenthrin, cyfluthrin, cypermethrin, deltamethrin, lambda-cyhalothin, permethrin and tralomethrin. Active ingredients are listed on the label. Be sure to follow label directions on each product to insure optimum results.

For more information on home gardening questions, call the Master Gardener Hotline toll-free at 1-877-252-GROW (4769).