News from the Farm: Armyworms marching into lawns, pastures, crops

It seems that they come earlier and earlier each year, but armyworms are back. The most common type that we are seeing now are Fall armyworms and they love grass crops. In this past week, I have observed armyworms in soybeans, hayfields, pastures, and in a bermuda grass lawn. Armyworms are a really bad pest because they have the ability to devour a lawn, pasture or hay field in a very short period of time. Many times they go unnoticed, as they cause most of the damage at night.

Hay producers and homeowners are sometimes given a warning that armyworms are in a field by the presence of white cow birds or a cluster of birds. But hay producers that are applying high levels of fertilizers to grow a quality crop should scout their fields every other day to make sure these destructive pests are not eating their hay crop. Scouting for Fall armyworms requires a hay producer to go into the field, push back the grass and look for worms.

Homeowners should be observant of brown patches of bermuda grass that rapidly spread and enlarge. If you see this, start looking for armyworms. The caterpillars feed at night, so the culprit of the damage is not noticeable at first. Scouting for homeowners can be a little different. To inspect your lawn for armyworms, simply mix about two tablespoons of a lemon-scented dishwashing detergent in one gallon of water and pour it over a one square foot area of the lawn. If armyworms are present, they will quickly come to the top of the sod.

Fall armyworms will eat many kinds of grass, but their favorite is bermuda grass that is well fertilized and watered. Homeowners frequently notice them after their grass starts to thin.

Armyworms are susceptible to cold and are unable to survive even the mildest winters in Georgia. Each year, Fall armyworm moths are carried by air currents 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.

The four stages of development of the fall armyworm are the egg, larvae, pupae and adult. The adult is an ash-gray colored moth. The front wings are mottled and have white or light gray spots near the tips. The back wings are white with a narrow, smoky-brown edge. The female moths lay eggs at night in masses of up to several hundred in grass and on light-colored surfaces. The eggs are light gray and covered with grayish fuzz from the females body. These masses darken with age and the eggs hatch within 2 to 4 days.

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 11/2 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.

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 to four generations can occur in southeast Georgia.

Fall armyworm damage often seems to appear suddenly overnight. The young armyworms do not eat very much. Almost all the damage is caused by the older caterpillars which eat more than all the other ages put together. Large fall armyworms will often march into an uninfested area in search of food once an adjacent lawn has been defoliated.

Several insecticides are available to homeowners that will provide effective control of fall armyworms; trichlorfon (Bayer Advanced), carbaryl (Sevin) 50WP, Bacillus thuringiensis (Dipel WP) and various pyrethroids. Always be sure to read and follow label directions.

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News from the Farm: Armyworms marching into lawns, pastures, crops