How to Get Rid of Armyworms

Armyworms are the larvae of a moth commonly found in the southeastern United States. These small moths have white hind wings and gray front wings that are mottled with darker and lighter splotches. The moths lay their eggs in clusters of 50 or more at the base of host plants or tree leaves.

When hatched, the tiny caterpillars are green, brown or black in color and grow to 1 1/2 to 2 inches long. They can be identified by their dark heads usually marked with a pale inverted “Y”. As they grow to more than an inch long, their bodies change to brown with a white stripe along the side and a reddish-brown head. The life cycle is about 28 days, and several generations can occur in a year.

Fall armyworms cause the most damage to home landscapes. Other species include yellow striped, beet and the true armyworm. 

Armyworm damage happens fast. Once they hatch, the caterpillars go on an eating binge for the next 14 days. They are most active in early morning and late evening in summer and early fall.

Depending on the size of the infestation, you could wake up to a patch of dirt instead of a green lawn.

Armyworms aren’t picky eaters and can attack many kinds of plants as they migrate in search of edible foliage. As they feed, larvae leave brown spots on the lawn. Grass blades that look chewed or ragged is a sure sign of an armyworm presence. A heavy infestation can shear blades to the ground. In addition to warm-season turf grasses such as Bermuda and fescue, they can attack agricultural crops.

Armyworms have a number of natural enemies and in most years the population can be kept under control. Natural predators like some varieties of wasps and flies are effective in keeping armyworms at bay. Ground beetles also help limit armyworm infestations. Birds, rodents and skunks can consume large numbers of larvae and pupae.

To control armyworms, keep your lawn healthy. Mow grass to the correct height for the variety and keep grassy weeds under control, as these can attract egg-laying adults. Best rule of thumb for mowing your lawn: when your grass reaches 3 inches in height, it's time to mow. Grass grows best at 2 1/2 inches and higher, so set your mower blade to that height for the first few cuts in spring. Never cut your grass shorter than 2 1/2 inches (or remove more than 1/3 the height).

Tip: Control armyworms before they appear in large numbers or the damage they cause can become extensive.

Treat your lawn with a lawn insect and pest control product when you notice leaf damage or see armyworms.

• Bacillus thuringiensis (B.t.) products can selectively control small armyworm larvae without harming beneficial insects. This organic pesticide is available as a ready-to-use spray or as a concentrated solution that must be applied by a tank sprayer. Re-treating is recommended because B.t. residue remains on turf for less than two days and washes away with rain.
• Spinosad is a bacterial product produced by fermentation and can be used to get rid of armyworms in the landscape and garden.

Tip: Always wear protective equipment like safety glasses and gloves when applying pesticides to reduce the risk of skin or facial contact.

There are a number of ways to get rid of armyworms without toxic pesticides. Use a labeled organic insecticide for natural pest management for armyworm treatment. 

• Beneficial nematodes are microscopic organisms that feed on many lawn and garden pests. There are different species of nematodes, so choose a species like Heterohabditis bacteriophora that preys on armyworms. Nematodes are sensitive to sunlight so apply them in the early morning or late afternoon hours or on overcast days. Water the treated area thoroughly. The nematodes can eradicate the armyworms in as little as 48 hours.
• Neem oil is effective at killing armyworms and other pests. Mix a solution of one to two teaspoons of pure neem oil in a spray bottle with a gallon of warm water and a teaspoon of liquid soap or insecticidal soap. Spray the solution on lawns and other affected areas like plants twice a week as a preventative measure.
• Another option is to purge any armyworms you see by hand. Pick off any armyworms from the lawn or plant and drop them in a bucket of soapy water to kill them.