Southern Army Worms – Spodoptera eridania
By George Giltner, Master Gardener
These caterpillars are famous for their voracious appetites for veggies, fruit, field and ornamental crops. Common garden vegetables attacked include sweet potatoes, cabbage, beets, carrots, collards, cowpeas, okra, peppers, tomatoes, watermelons, and peanuts. However their favorite plants are pigweed, Amaranthus spp., and pokeweed, Phytolacca americana. They may start in an area with these weeds, then venture into surrounding crops in the garden.
The southern army worm caterpillars can be identified with their smooth, light brown to reddish brown heads and a maximum length around 3.5 cm. The larvae are green or blackish green with a white dorsal stripe and yellow lateral stripes which are broken by a dark spot on the first abdominal segment. The smooth caterpillars are found on the underside of leaves. Their most active period is at night. The larvae cycle time is two to three weeks. Then the larvae pupate in the soil for two weeks.
The adult moths are about 3.5 cm in wing span. The forewings are gray and brown with irregular back and dark brown markings. The wing pattern is highly variable, but the hind wings are whitish. The green to tan eggs are laid in clusters, then covered with scales from the female moth. They hatch in 5 days.
Natural predators are wasp parasitoids including Braconidae, Ichneumonidae, and Eulophidae. Predatory stinkbugs also prey on armyworms. Broad range insecticides may damage these natural predator populations. Caterpillars are also susceptible to the fungus, Beauveria bassiana.
Southern armyworms are best controlled early with foliar insecticides. Botanical insecticides are not very effective. “DiPel DF” and “Deliver” are two Bt products to try. Use at higher rates. Combinations of diatomaceous earth and pyethrins, “Diatect V”, are effective. Spinosads like “Entrust” work but do not make applications less than 7 days apart or apply more than 4 times per crop. Additional treatments for control can be found at edis.ifas.ufl.edu/ig159.
Our experience with sweet potatoes is to begin control early or suffer extensive crop damage.