Overview
Armyworms are stout-bodied, hairless, striped caterpillars that chew the foliage of grasses and grain crops. They are named because of their habit of crawling in large numbers from field to field when they have exhausted their food supply. Newly hatched larvae are greenish, and older ones are 1.5 in. long and range in color from light tan to olive green to nearly black, and have stripes along the sides of their back.
Several species of armyworms may attack turfgrasses. Homeowners and golf course superintendents are understandably concerned when their turf is literally mowed down by an “army” of caterpillars that seems to appear overnight. These pests are sporadic, but have an ever-present potential for outbreaks.
There are three major species of armyworms that attack turf in the United States. "True" armyworm ( Pseudaletia unipuncta ), Fall armyworm ( Spodoptera frugiperda ) and lawn armyworm ( Spodoptera mauritia ).
"True" armyworms are especially fond of corn and small grains, but will feed on all common turfgrasses. This species probably does not over-winter in the Northern half of the U.S. but annual infestations in the Central and Northern armyworms parts of the U.S. result from the northward migrations of moths in the spring. These armyworms are gregarious and tend to feed as a group, devouring circular patches of turf before moving on to another food source. They tend to hide in the thatch during the day and most of the damage occurs at night.
Fall armyworms are like "True" armyworms, but the damage they cause is more uniform over a broader area. These insects feed anytime during the day or night but move about mostly in the dark or early morning. Fall armyworms can be distinguished from “True” armyworms by the more prominent inverted Y-shaped marking on the front of the head and the presence of 4 distinct black tubercles on the back of each abdominal segment.
Lawn armyworms are a major pest of Bermuda grass in Hawaii. The injury is like that caused by the “True” and Fall armyworm. Adult (moths) "true" armyworms are uniformly pale brown to grayish brown with a wingspan of about 1.5 in. Adult fall armyworms and lawn armyworms are the same size as “True” armyworms but are dark gray. Adult moths generally remain hidden by day but become more active at night and are attracted to light.
Management
Applications of Talstar ® Professional or Talstar ® Select at a rate of 0.18-0.25 fl.oz./1,000 sq ft are sufficient. To ensure optimum control, delay watering (irrigation) or mowing for 24 hours after application. If the grass area is being maintained at a mowing height of greater than 1 inch, then higher application rates (up to 1 fl. oz. per 1000 sq ft) may be required during periods of high pest pressure.