By Kathleen Cue, Nebraska Extension Horticulture Educator in Dodge County (Week of September 6, 2021)
The fall armyworm, Spodoptera frugiperda, is a pest of row crops and lawns, preferring Kentucky bluegrass above other types of lawn grasses grown in the region. The caterpillars eat the blades of grass, to the point of turf thinning and browning. Sixth instars, the largest they’ll grow as caterpillars, are 1-¼ inches long with 3 stripes extending along their length and an inverted “Y” shape on their head. Pupation takes place in the turf, with the adult moths emerging to mate. Sources differ on the number of eggs each female produces but it is many, ranging from 100 to 1000. Egg masses can appear on buildings, fences, plants, and outdoor furniture. Eggs develop into first instar caterpillars in just 2-5 days. Initially, feeding is minimal, owing to the caterpillar’s small size, but as they grow, their appetite increases and the damage they cause more readily apparent.
The FAW is a tropical pest, overwintering where winters are mild, in southern Florida and Texas, and blown to northern locations via storms and the accompanying winds in summer. The “fall” in its common name refers to caterpillars becoming prevalent in late summer and early fall and “armyworm” references the caterpillars moving across the lawn in a line, eating everything as they go. FAW has no diapause, a suspension of development to successfully overwinter harsh winters like some of our native insects do. The FAW will be active until the first freeze at which time all feeding and activity by the FAW ends—at least until next year’s storms blow moths into our region.
Insecticides will be most effective when caterpillars are newly-hatched and damage is not noticeable. To monitor for the FAW, mix a container of soapy water and dump it on the lawn. If the caterpillars are present, they will move above the lawn’s surface. Insecticides containing one of these active ingredients are effective against the fall armyworm: carbaryl, chlorantraniliprole, azadirachtin, Monterey B.t., spinosad, and bifenthrin. Once the lawn is free of the FAW, overseeding may be necessary to fill in thin areas. More information about the fall armyworm may be found here: https://www.turffiles.ncsu.edu/insects/fall-armyworm-in-turf/
Photo attribtued to: Russ Ottens, University of Georgia, Bugwood.org