Armyworms in Pasture and Turf
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.
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.
Few insecticides are labeled for use on armyworms in pastures. The most consistently effective are Lannate and Sevin. Lannate requires a 3-day harvest or 7-day grazing interval. 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.
Originally compiled from