Fall armyworms are early this year

We are in the first half of June and have already had reports of fall armyworms in forage and hay meadows in southwest Arkansas. These reports indicated worms above treatment threshold (three worms per square foot) and of mixed sizes. Mixed sizes of worms indicate overlapping generations which means that adult female moths can be laying eggs anytime to re-infest.

Fall armyworms are caterpillars that appear in large groups and cause damage by feeding on the leaves of green turf (usually Bermuda grass). The larvae (worms) can be white, off-white, yellow or light green in color after they hatch and then darken in color as they develop. Once they mature, the fall armyworms are about 1.5 inches long. They are easy to identify by the presence of an upside-down Y marking on their head with white stripes down their body. The worms can quickly (in a matter of a few days) turn a green turf or a pasture into a brown area by feeding on the leaves across the area. The worms are a problem and a great nuisance until they’re subjected to a hard frost in late October or November.

Fall armyworms do not over-winter in Arkansas; instead, the adult moths catch wind currents and gradually move into our state from the south and lay eggs. Fall armyworm damage can appear almost overnight. Infestations can be easily overlooked when the caterpillars are small and eating very little, but once they grow large and eat more, the damage becomes readily apparent.

There are a few tips to remember about fall armyworms. First of all, do not treat your lawn when armyworms are tiny; however, get prepared. Several natural enemies such as parasites, predators and pathogens occur and can possibly eliminate or reduce populations in a very short period of time, thereby saving you the effort. The fall armyworm has about six larval instars (“instar” is the developmental stage of arthropods). The last few, particularly the fifth and sixth instars, are when most of the damage occurs. Of the total foliage consumed, greater than 80-85 percent will occur at these stages. The best advice is to not get overanxious and treat before it’s really necessary. But, do not wait until they become too large either. Most of the recommended products will work well on medium-sized larvae.

If you decide to treat the armyworms, liquid, not granular, insecticides are usually best. Any sprayable lawn insecticide can be applied in a coarse spray over the grass. Wet the grass thoroughly and do not mow for three days after application.

Several lawn insecticides are effective caterpillar killers; however, products containing B.T. are effective only on small (1/2 inch or less) worms. Irrigate the grass before treating, to move the caterpillars out of the thatch. Treat in late afternoon, as this is when the caterpillars are likely to be feeding. If possible, mow before you treat and then do not mow for three days after treatment. Winter cold has a great effect on armyworm populations. If a winter is severe, only a few of them will survive for next year. The good news is that armyworms will not hurt your lawn permanently. Since they feed on the grass blades and not the roots, they rarely, if ever, kill the grass. But lawns can be weakened by this voracious eater, especially if they have suffered through harsh growing conditions.

For more information on controlling armyworms, see Extension fact sheet FSA 7083 “Managing Armyworms in Pastures and Hayfields,” http://www.uaex.edu/publications/PDF/FSA-7083.pdf. Information about managing fall armyworms can be found at http://www.uaex.edu/counties/prairie/fall%20armyworm%20sheet%202015.pdf. To contact county agent Allen Bates, call 6236841, or email him at abates@uaex.edu.

Master Gardener

If interested in gardening, the public is welcome to attend the monthly Master Gardener meeting at 1 p.m. on the third Thursday of each month at the Elk’s Lodge. For information, call the Extension office at 623-6841 or email Allen Bates.

EHC

Interested in joining an Extension Homemakers Club or forming a new club in the community? For information, email jvincent@uaex.edu.

4-H

If between the ages of 5 and 19, you can join

4-H. We have a club for you, or you and a group of friends can organize your own club. For information, call the Extension office or email lbates@uaex.edu.