In late summer, almost every year, armyworms invade pastures, hay fields, and turfgrass throughout the state. Particularly in pastures and hay fields, damage may be severe before the worms are noticed. The grass is not killed, but hay yield and forage can be reduced to almost nothing over whole fields in extreme cases. The damage to established turf is mostly aesthetic, but newly sodded or sprigged areas can be more severely damaged or even killed. Although somewhat early, it is not too early to start scouting for the fall armyworm to help avoid a pattern like we saw last year. Last year was worst year that many of us can remember for forage production between the drought and the army worms forages were limited. And even the army worms were more persistent last year than they were in previous years. Hopefully with the rainfall this year at least it will help with the quantity of hay that our producers were able to harvest.
Most of the worms are fall armyworms. The adult moths are active at night and females lay eggs in batches of 50 to several hundred. Eggs hatch in 2 – 10 days, and the young larvae begin to feed on leaf tissue. Damage from small larvae may at first look like skeletonizing, but as the worms grow, the entire leaf is consumed.
Armyworms are most active early and late in the day, spending the hotter hours down near the soil in the shade. Larvae feed for 2 to 3 weeks before pupating in the soil. Moths emerge 10 – 14 days later.
Several insecticides are labeled for use on armyworms in pastures. The most common for individuals without a private pesticide licenses is probably Sevin. A number of pyrethroid insecticides are also labeled and are effective. For Sevin, the interval is 14 days. In any case, if the hay is close to ready, cut it before treating. It also helps to increase your spray volume as much as possible, particularly with Sevin on larger worms.
Recognize that very large worms are tough to kill and the best option may be to wait until the next generation and target the smaller worms. Sometimes, the next generation will move on and no treatment will be necessary.
Turf managers have many more options, and almost every insecticide with caterpillars or armyworms on the label will provide good control. Again, spray volume is important to improve the chance of controlling larger worms. If there is any doubt about whether worms are present, pouring soapy water on the grass (1/2 oz. dishwashing soap/gal.water) will bring them up very quickly.
If you have questions about armyworms in turf or forage and treatment options, call the UGA Extension Office at 706 384-2843.