Extension‐Wise
Published Weekly in the Madison County Journal Fall Armyworms August 2, 2012 Few things will strike fear into the hearts of pasture and hayfield owners like knowing that fall armyworms are on the march. These pests can quickly decimate a field or bermudagrass, fescue, pearl millet, and several other crops and then disappear as quickly as they appeared. Reports have been coming from across more southern parts of the state but we have now go en first reports of fall armyworms in Madison County. Growers and even homeowners will need to keep a close and frequent lookout for signs of these pests. Fall armyworms can be up to 1.5 inches long and are light green to nearly black with light and dark stripes that stretch horizontally along the body of the worm. One of the most dis nct characteris cs used to iden fy armyworms is an inverted “Y” on the head of the worm. As the name implies, fall armyworms are most numerous in late summer and early fall, meaning right now is a prime me to start looking for poten al infesta ons. They are unable to tolerate even a mild winter, but each year moths are carried by wind currents from Florida and Central and South America which then lay eggs throughout the south. Armyworms cause damage by chewing on plant ssue. They are typically most ac ve in early morning or late a ernoon when temperatures are cooler. In newly cut hay or shorter grass, armyworms will hide in thatch and top soil layers during the heat of the day but they could be seen foraging in tall grass during any part of the day. Armyworms go through 6 stages of larval development. The very young larvae do not eat much but the mature larvae can eat more than all other ages put together. Damage can appear differently depending on the type of forage and condi ons. On closely grazed pastures, damage may appear as thinned out grass and brown spots, which could be misdiagnosed as drought damage. In hayfields or pastures with tall growth, damage can be devasta ng with nearly all tender green vegeta on being removed. Established, healthy bermudagrass is not likely to be totally killed by armyworm infesta ons, but the damage caused by a complete infesta on will weaken the plant and result in reduced forage availability for livestock. Armyworm damage is some mes described as “coming in waves.” If you no ce armyworms in your field, you will need to keep a close eye over the next few months on that field and any surrounding fields to look for subsequent genera ons that have hatched. You should start looking at least two weeks a er ini al damage has occurred for any young larvae. Treatment thresholds are typically recommended at three armyworm larvae found per square foot. It may be necessary to treat with an insec cide under certain condi ons. It should be stated that young larvae are much easier to kill than adult armyworm larvae and thorough scou ng may allow to only spot treat certain areas of fields. Harves ng a hay crop may be the best op on for armyworm control if hay is close to cu ng me. Several insec cides are available that have control over armyworms, including carbaryl (Sevin and others), diflubenzuron (Dimilin), cyfluthrin, spinosad, zeta‐cypermethrin (Mustang Max), and others. Careful a en on must be made to any grazing or harves ng restric ons related to these products. Careful scou ng has been men oned as the best way to prevent economic losses. Watch for flocks of birds that may be congrega ng as a sign of infesta on. If you see areas of dead grass star ng to appear, look on the grass and also in the thatch layer for any signs of armyworms. Purchasing an insect net and performing sweeps early in the morning and late in the a ernoon is a quick and easy way of scou ng. If infesta ons do occur, it is best advised based on ming to fer lize the field to provide addi onal hay cu ngs or rest a pasture from grazing to allow for the forage to reestablish itself. If you no ce what may be armyworms, contact the Extension office for more specific recommenda ons and consulta on. Here’s hoping we keep this army at bay this fall.