Three beneficial entomopathogenic nematodes for the control of fall armyworms
As name implies, fall armyworms occur every year during fall season and their larvae (caterpillars) march like “armies”. Only larvae of fall armyworms cause a serious damage to different crops like corn and sorghum, and turf grasses especially bermudagrass, bluegrass, Johnsongrass, Sudangrass and ryegrass.
Fall armyworms belong to an insect order Lepidoptera. They are scientifically known as Spodoptera frugiperda. Front and hind wings of adult moths are dark grey with dark splotches and whitish in color, respectively (Photo 1 and 2). Fully matured larvae are about 30-50 mm long, black or brown in color with a longitudinal black stripe on each side of body, they have four black spots on their dorsal side of the abdominal segments and a distinctive pale colored inverted “Y” shaped mark on their heads (Photo 3). Eggs are light grey in color and covered with the fuzzy scales. Pupae are reddish brown to black in color.
Life cycle of armyworms
The life cycle of fall armyworms consists of four stages including eggs, larvae (caterpillars), pupae and adults. Fall armyworms overwinter in the warm regions in the south but they generally begin migrating towards the north when temperature starts warming up in the spring. During migration, armyworms complete several generations and that is why a large numbers (armies) of larvae appear in the late summer and early fall in northern states. Female moths lay eggs in batches of a few dozens to several hundreds on any vegetation. Eggs hatch within 2-10 days into small larvae that immediately start feeding on new growth of grass. While feeding larvae grow rapidly, mature within 2-3 weeks, become 30-50 mm long (Photo 4) and then pupate in the soil/upper thatch layer. Adult moths then emerge from pupae within 10-15 days and thus the entire life cycle is completed within 28-30 days.
Damage caused by armyworms
Only larval (caterpillar) stages (Photo 3 and 4) of armyworms feed and cause a serious damage to many plant species including turf grass. The symptoms of feeding damage by armyworm larvae include partly skeletonized or entirely consumed leaves. Newly born larvae generally skeletonize leaves whereas matured larvae can consume entire leaf. Larvae feed for 2-3 weeks before pupation. Although fall armyworms feed on the grass any time of the day or the night, they are more active early in the morning and late in the evening.
Biological control of armyworms
Control of armyworms is essential because of the intensity of damage caused their larvae that can voraciously feed on grass and completely destroy hay in the sod farms. Chemical pesticides are effective in controlling armyworms but their use in sod farms should be restricted due their toxic effects on human and animal health, and the environment.
Beneficial entomopathogenic nematodes like Heterorhabditis bacteriophora, Heterorhabditis indica and Steinernema carpocapsae have been proved to be human and eco-friendly alternatives to chemical pesticides in controlling many soil-dwelling insect pests including armyworms. Since armyworms are very susceptible to beneficial nematodes, now is the best time to apply them (23000 nematodes per sq. ft.) to target armyworms because both of their young and mature larvae are now actively feeding and destroying the hay in most of the northern regions. Apply beneficial nematodes early in the morning or late in the night because during these timings, armyworm larvae are very active and therefore they can be easily found by the nematodes. Another advantage of applying nematodes during these timings is that nematodes can die instantly if they are exposed to UV light.
Recommended rates of beneficial entomopathogenic Heterorhabditis bacteriophora, Heterorhabditis indica and Steinernema carpocapsae nematodes for different size areas.
Area in sq. ft. = Number of nematodes required
43,560 (1 Acre)………….1,000,000,000
Please read “how beneficial nematodes kill armyworms“.