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Armyworms feed on turf grasses, causing large brown patches in lawns.

Sod webworms were biblical last summer. Not to be outdone, the armyworm troops have now set up camp. They are out in full force, causing headaches for many homeowners.

If you’ve noticed large brown patches in your lawn, it may be damage from armyworms, which feed on turf grasses such as Bermuda, St. Augustine and centipede in addition to other agricultural crops.

In fact, that's how these caterpillars got their name. As they destroyed large agricultural areas in just days, they resembled an army troop on the march.

Most homeowners will not notice the damage until large patches of grass begin to die. Once the caterpillars have consumed a large area, they move on to nearby fields and lawns.

It’s a good practice to scout your lawn in the summertime for damage from armyworms, chinch bugs and sod webworms to stay ahead of extensive damage.

You might notice the adult moths of armyworms flying around outdoor lights at night when they are active. The moths are gray to light brown and are small, with a wingspan of 1 to 2 inches. The upper wings are brown with white spots, and underwings are white.

Like most other insects, the armyworm has four life stages: egg, larvae, pupa and adult.

Females lay thousands of eggs on leaves and stems of plants or structures near lawns. Eggs hatch and larvae develop in about two to three weeks. Then they go down into the ground to pupate and emerge as adults in one to two weeks. Unfortunately, there are several generations of the armyworm per year.

With the hard freezes experienced across the state in February, it’s a bit of a surprise to see such an infestation of armyworms because they are typically susceptible to extensive cold weather. However, outbreak years like the one we are experiencing do happen from time to time.

Damaged areas of the lawn may resemble drought stress, but you will be able to tell that it is insect damage when a distinct line is seen between the damaged areas versus undamaged.

The caterpillars are most active in early morning and late evening hours, and they can be observed flying around outdoor lights.

When scouting for grass damage, look for chewed leaves that are translucent on the ends. You may also find green frass (caterpillar poop). Leaves also may look skeletonized. Another great indicator is large groups of feeding birds.

Initial damage is low, but as larvae grow, they consume more plants and damage becomes more rapid in the later stages of development.

Early detection is important. Large numbers of armyworms can cause extensive damage, so take time to walk around before you mow and look for caterpillars and signs of damage.

There are a couple of forms of organic control. Products that contain the active ingredients Bt (Bacillus thuringiensis) or spinosad are considered organic options. For heavy infestations, synthetic chemicals may be necessary. Effective products contain one or more of the following active ingredients: acephate, bifenthrin, carbaryl or clothianidin.

Read and follow all label instructions. Chemicals will need to be repeated in seven to 14 days to treat newly hatched eggs.

When using insecticides, beneficial insects and the animals that feed on them in addition to pollinators could be harmed. Spray very early in the morning or late in the evening when pollinators are less active.

For more information on the responsible and safe use of pesticides for turfgrass insect pests, go to LSUAgCenter.com and search for “Louisiana Insect Pest Management Guide.” For more information on fall webworms in turfgrass, search for “Louisiana Home Lawn Series: Fall armyworm.”

Healthy and actively growing grass will likely recover fully, even after a heavy infestation and extensive damage. Lawns recover more quickly with their aggressive root growth by rhizomes and stolons that spread across the lawn.


Email questions to gardennews@agcenter.lsu.edu.