Fall Armyworms

Brown caterpillar on green leaf
Fall armyworm caterpillar. Photo: Lyle Buss, UF/IFAS.

Despite their name, fall armyworms cause damage to turfgrass in spring and fall. Damage from fall armyworms is uniform across a large area and results in bare spots in a lawn. While they are active at all hours, they do most of their feeding in the early morning and late evening. Fall armyworms tend to be more of a problem on newly established turf, especially if the turf was heavily fertilized in late summer. Just one reason why it is necessary to the health of your lawn to fertilize appropriately and at the correct time.

Fall armyworms are green to brown colored caterpillars when young and dark brown when they mature. They reach up to 1.5 inches long and have a dark head marked with a light colored inverted Y.

If you suspect fall armyworms are to blame for the damage to your lawn you can perform a relatively simple test. Start by mixing one tablespoon of liquid dish soap in one gallon of water. Pour this soapy water solution onto a four-foot by four-foot area of turfgrass near the damage. If fall armyworms are present, they will crawl to the surface; you can test several areas to be sure.

Beyond testing your lawn for the presence of caterpillars, you may also see adult moths flying towards lights in your landscape at night. The moths are brown with white-tipped forewings and have a 1.5 inch wingspan.

You can also be on the lookout for groups of eggs that have been laid in your landscape. Eggs are laid in clusters on the tips of leaf blades or light-colored surfaces adjacent to turf. The eggs are light green when first laid and darken with age and are dusted with gray, fuzzy scales.

Fall armyworms are often controlled by their natural predators, like wasps and other predatory bugs. Be aware that pesticide applications can affect these natural predators, so keeping your lawn healthy and well maintained is the best to prevent rather than treat for a pest.

Once you have an idea of what pest you are dealing with, you can contact your county Extension office for information on treatments.

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