Arkansas is home to Fall Armyworms which is one of the most devasting pests of pastures, hayfields, lawns and athletic fields by reducing forage availability and hay yields. The fall armyworm has been an annual pest on crops and turf in the South for more than 100 years. Armyworms are most noticeably seen “marching” in large numbers across lawns. They often feed openly and conspicuously, sometimes during the day, making themselves relatively easy to spot. Most armyworms are large caterpillars with long stripes lengthwise on the body and some netlike pattern on the head.
Damage can appear overnight and infestations can be easily overlooked when the caterpillars are small and eating very little. Beginning as early as late June and into early July significant fall armyworm populations can occur in Arkansas. They attack a variety of plants, including turfgrasses but seem to prefer well-fertilized and well maintained bermudagrass. Fall armyworms also attack fescue, ryegrass, bluegrass, and bentgrass.
Fall armyworm caterpillars damage grass by chewing plant tissue. They are the most active on turf in early morning or late afternoon/early evening, but they may feed any time of the day. Fall armyworm damage to turf may vary in appearance and severity with bermudagrass being the most common host. Fall armyworm damage often appears as a browned or burned-out patch resembling drought damage. The damaged patch will usually increase in size as the fall armyworm consumes more foliage. The brown color results from drying of the plant due to dehydration after armyworms chew tender growth. Often, after a severe fall armyworm infestation, the only vegetation left in the field will be tough stems.
To control fall armyworms proper timing of an insecticide application will result in better control. In most cases, insecticide control is warranted when an average of three of more worms per square foot occurs. The best type of equipment to apply insecticides for armyworm control is a properly calibrated boom sprayer or lawn gun. Once applied stop all irrigation for a minimum of 24 hours post application. Once the insecticide application has been applied the grass will recover by having some new growth and within a couple of weeks you will not be able to tell the damage that used to be present.