Fall Armyworms

Insect Name: Fall Armyworm, Spodoptera frugiperda

Description: Armyworms belong to the insect order Lepidoptera (moths and butterflies) and family Noctuidae (night flying moths). They go through complete metamorphosis. Fall armyworm adults are generally gray in color with white markings, which includes a white teardrop-shaped light mark on the forewing. The adult moths are very susceptible to the cold, but do overwinter in Texas. All life stages can be found during the entire year. The moths fly and mate at night, after which the female will lay about 1,000 eggs in masses on structures near turfgrass (Figure 1). The adults live about 1 to 3 weeks and take 23 to 28 days to complete a generation. The eggs hatch and the 1st instar caterpillars (larva) emerge and begin feeding. They range in color from pinkish to yellowish, greenish, and dull gray to almost black. The top of their heads will have a light-colored (typically yellowish) inverted Y (Figure 2). They typically feed at night and will go through two more molts before pupating (Figure 3) into the adult moth and starting the lifecycle over.

Distribution and Host Plants: Fall armyworms occur throughout the east coast, through the southern and Gulf States into Arizona and the southern tip of California as well as northward, east of the Rocky Mountains, to Canada. The caterpillars prefer to feed on bermudagrass, fescue, ryegrass, and bluegrass.

Damage: Damage by fall armyworm caterpillars initially appears at the tips of the grass blades where they appear transparent where the plant cells have been eaten. If left uncontrolled, the caterpillars will continue feeding and leave large areas of dead turf (Figure 4)  adjacent to healthy turf, and usually there is a sharp distinct line between damaged and undamaged areas. (Figure 5). Damage to bermudagrass often resembles drought stress, but can be recovered after treatment. However, feeding on newly established ryegrass or fescue may cause stunting of the plant or eventual death if left untreated.

Monitoring: In order to determine life stages, populations can be monitored using a soapy-water flush, which is 2 tablespoons of lemon-scented dish detergent in 2 gallons of water. Pour the solution over an area of 1 yd2 in undamaged turfgrass that is in close proximity to damaged turfgrass. Watch the area closely for caterpillars that emerge within 10 min of the soapy-water application. If the turf is severely damaged, then the caterpillars may have moved deeper into the soil profile to pupate, and thus would not emerge from the soapy-water flush.

Control: For a list of insecticides registered in Texas for control of fall armyworms please see the Texas Turfgrass Pest Control Recommendations Guide. Timing is key for effectively managing fall armyworms. Applications need to be timed when the caterpillars are small, 1st instars. Be sure to mow and lightly irrigate prior to insecticide treatment and do not mow for 1-2 days after treatment.