How they eat

When feeding, larvae strip foliage and then move to the next available
food source. High populations appear to march side by side to the new food. Thus, the name armyworm is derived.  Damage consists of
defoliation. The small larvae will chew the green layer from the leaves,
creating a “window pane” effect. The first three instars cause very
little feeding damage while the last two instars consume 85% of the
total foliage consumed.

What they eat

Fall armyworms feed on a wide range of plants, including Bermudagrass, Bentgrass, Bluegrasses, corn, fescue, Johnsongrass, rice, ryegrass, small grain crops, sorghum, soybeans, Sudangrass and timothy. In corn, caterpillars can injure foliage as well as the ears. In soybeans, they eat the pod as well as the leaves.  Lush plant growth is preferred by the adults for egg laying.  Caterpillars often occur locally in large numbers and migrate together like an army as they devour host plants, eating all above ground plant parts. They feed at all times of the day or night.  In lawns or grasses you will see circular to irregular, dead patches and leaf blades will appear transparent from plant cells being eaten.  Large grass areas may be eaten to the soil surface during severe outbreaks.  Green excrement frass may be present in feeding areas.

What they look like

Armyworms have four life stages: egg, larva, pupa and adult.  The adult moth is a siphoning insect.  The larvae (caterpillar/worm) is a chewing insect and this stage does the most damage.
Winter is spent primarily as pupae, although all stages may be
encountered during mild winters. Adults (moths) emerge in early spring, mate, disperse and lay eggs on host plants. They lay clusters of a hundred or more eggs on leaves at night and cover them with light grayish fuzz.

Larvae (caterpillars/worms) hatch from the eggs in about 10 days and
begin feeding together, first on the remains of the egg mass and then on the host plant.  They curl up inside leaf sheaths, suspend from plants by threads, and move about soil surface.   Newly hatched larvae are white with jet black heads.  They mature in about 3 days and have heads with an inverted white Y.  When fully grown, they are 1 1/3 inches to 2 inches long and are marked with green, brown or black colors arranged in stripes, with darker stripes along the sides.

The top of each abdominal segment is marked with two pairs of black dots from which stiff hairs arise. 

Larvae grow and molt in five stages (instars) over a period of 2 to 3
weeks before digging a burrow 2, 3 or up to 8-inches deep in the ground in which to pupate. The larvae sometimes hide in debris on the soil surface in the middle of the day.  The pupa is about ½ inch long, reddish brown to black, smooth and hardened.

Fall populations of larvae often blend together several generations and may appear to be continually occurring.  Adult moths emerge in about 2 weeks. Several generations (a generation is the development from egg to adult stage) occur each year and typically take about 28 days to complete.  There can be as many as ten generations in a year.

Adults are about ¾ inch long and 1 ½ inches across outspread wings.
They have dark gray mottled forewings marked with light and dark areas. Hind wings have a pinkish-white luster, bordered by a smoky-brown band. Wings are held over the back of the body when at rest. The hind wings are white. 

Why they live here

1.  They thrive in warm humid climates. 
2.  They don’t like cold winters. 
3.  We grow a large number of their host plants.

How are they controlled

Although armyworm outbreaks are memorable when they occur, in reality, the outbreaks are usually small in scope. Weather and natural enemies usually act together to keep populations under control.
Parasites such as wasps and flies are very effective against armyworms.

Predators, such as ground beetles, are also effective in limiting
outbreaks. Birds, skunks and rodents consume large numbers of larvae and pupae. Diseases such as insect viruses and fungi can also be important control agents.

However, conditions can occur that favor armyworms. High egg survival of fall armyworms is favored by above average rains in August and September.   Because armyworm moths are strong fliers, outbreaks can also occur when storms move the moths and allow them to escape natural enemies.

Armyworms should be controlled when they occur in large numbers or
plant damage is becoming excessive. Since fall armyworm outbreaks
usually occur late in the summer and early fall, preventive treatments
normally are not justified because attacks are sporadic and egg
mortality is usually high. A variety of natural enemies keep fall
armyworm larvae down to moderate numbers. Early detection of larvae is the best management tool and is achieved by frequent, thorough inspection of plants. Outbreaks seem to occur shortly after a rain or supplemental irrigation.

Fall armyworms feed any time of the day or night, but are most active
early in the morning or late in the evening. Susceptible fields or lawns
should be scouted by counting the number of armyworms in a square foot area in 8 different sites. Divide the total worm count by 8 to find the average number of armyworms per square foot. Be sure to take samples in the interior of the field because this pest is often heaviest near the field margins. Sometimes, only the field margins require treatment. The threshold level ranges from two to three larvae per square foot for seedling wheat. For older plants, three to four larvae and obvious foliage loss justify control measures. Thresholds in improved pastures and lawns vary with conditions but treatment should be considered when counts average three or more worms per square foot.

Insecticide labeled in lawns and turf include halofenozide (Mach® 2),
bifenthrin (Talstar®), cyfluthrin (Tempo®, Bayer Advanced®), carbaryl
(Sevin®) permethrin (multiple brands) and spinosad (Conserve® and
others).

Pesticides should be applied in late afternoon or evening with
irrigation delayed until the next day.

In turfgrass, caterpillars may be driven to the surface by sprinkling
soapy water onto infested areas. Adult moths are attracted to lights and pheromone traps.

Insecticide choices vary with the crop but the following (with product
names and grazing restrictions in parentheses) are labeled for use in
pastures include carbaryl (Sevin®) (14 days), malathion (0 days),
methomyl (Lannate®) (7 days), methyl parathion (Penncap®-M) (15 days) and various biologicals such as Dipel®(0 days).

The following AgriLife Extension publications contain information about the fall armyworm:  B-1220, Managing Insect and Mite Pests of Texas Sorghum; B-1251, Managing Insect and Mite Pests of Small Grains; B-1401, Integrated Pest Management Guide for Texas Forage Crops; E-5, 6 and 7 Managing Insect and Mite Pests of Cotton; and EEE-0009,  Armyworms in Texas Pastures and Lawns.

For more information contact the Fannin County AgriLife
Extension office at 903-583-7453 or visit at 210 S. Main in Bonham.