The adult moths are active at night laying eggs in bunches of 50 -100. Eggs hatch in 2 -3 days and the young caterpillars begin to feed. Feeding from young worms causes skeletonized leaves on grass blades but as the worms grow the entire leaf, mid rib and leaf stalk can be eaten.
The caterpillars are most active early and late in the day. These caterpillars are 1.5 to 2 inches long when full grown, and the color varies from light tan to green to nearly black. A tan colored stripe runs down each side of the caterpillar and as they become about an inch long they develop an upside-down Y marking on their forehead. The caterpillars feed for 2 -3 weeks until they go into the soil and pupate. In about 10 -14 days adult moths emerge and start the egg laying process over again. The day you find worms on your farm or in your yard; you can look on a calendar and predict the next outbreak in 4 - 5 weeks.
Armyworms attack pastures, hayfields, and even turf areas. Extremely dry, hot weather is the welcome mat that invites army worms to our area. The grass is not killed; however the plants’ leaves disappear as the caterpillars consume the grass.
In a lawn, there is no big deal, the grass will regrow in 2- 3 weeks. But for farmers, the loss could be a $1,000 worth of fertilizer wasted and winter feed purchased due to lack of hay.
Most of us with only yards to look after, automatically grab the sprayer to fight the pests who dare consume our manicured lawns. There are many products for the homeowner to do battle with. Just about any insecticide labeled for outdoor use will control armyworms. The point to remember is that larger worms require larger volumes of spray, smaller worms can be controlled with lower concentrations and lower volumes.
For homeowners concerned with pesticide usage there is a great organic alternative - Bacillus thuringiensis. Bacillus thuringiensis is sold under the names “Dipel,” “Safer Caterpillar Killer,” “Green Light BT Worm Killer,” “Caterpillar Attack” and others. This is actually a naturally occurring soil bacteria that is deadly on most caterpillars, but harmless to mammals and birds. It is also great on caterpillars in the vegetable garden. Sevin and many Pyrethrin based insecticides will also control armyworms. If you find an outbreak in your yard should you spray? Unless you have a newly established lawn, either by seed or sodding, the worms will probably not destroy your grass. However, worms that have been stepped on or driven over leave the most interesting colors on concrete.
Again, farmers have a little more at stake when it comes to the decision to spray or wait. There are several insecticides labeled for use on armyworms on pastures and hayfields. Larger worms are harder to control so in many haying situations, if the hay is almost ready to cut, the best option is to cut the hay instead of treating. The worms will not eat grass in the bale or grass that is cut ready to bale.
For pastures the best idea is to congregate cattle on pastures with armyworm outbreaks to let the cows out compete the worms. Try to move cows to pastures with taller grass to stay ahead of the worms. Treating with an approved insecticide sometimes is the best solution, but can add to the costs of running your farm.
Feel free to call on the Barrow County Extension Office (770 307-3029) for help identifying these pests and control advice.
Britt West is the extension agent for Barrow County. You can reach him at firstname.lastname@example.org.