Call in the troops

The yellowstriped armyworm, Spodoptera ornithogalli, is an insect pest of tomato (Solanum lycopersicum) and pepper (Capsicum annuum) crops grown in hoop houses and greenhouses. The caterpillars (larvae) feed on tomato leaves and tunnel into the fruit of tomato and pepper (Figs. 1 & 2).

Biology and life cycle

Development time from egg to adult is between 30 to 90 days, dependent on environmental conditions such as temperature. Females lay eggs in clusters of 200 to 500 with individual females capable of laying >2,000 eggs during their lifespan. Larvae hatch from eggs and there are six larval instars (stages between molting). Older caterpillars are 40 to 50 mm (1.5 to 2.0 inches) long, and brown, gray to black with two distinct yellow-orange stripes extending along each side of the abdomen (Figs. 3 & 4). Two black triangle-shaped spots are located on top of each abdominal segment (Fig. 5). The head is brown with black markings and has a light-colored inverted ‘V.’ Larvae feed for about three weeks and black fecal deposits (frass) may be present on the upperside of plant leaves.

The yellowstriped armyworm overwinters as a pupa in the soil with the larva initially creating a cell that is lined with silk. There are three to four generations per year. Adults eclose (emerge) from pupae in April through May. Adults have front wings that are patterned gray-brown with light and dark markings. There is a tan to brown diagonal band near the center of the wings. The hind wings are white with a narrow brown margin (Fig. 6).

Management

Scout regularly by randomly looking at plant leaves to detect early infestations. Insecticides can be used against yellowstriped armyworm caterpillars but they need to be applied when the caterpillars are small (young). For instance, Bacillus thuringiensis subsp. kurstaki (Btk) and spinosad can be used when the caterpillars are small and before they tunnel into fruit. Both materials are stomach poisons, so the caterpillar has to ingest the material to be killed. Thorough coverage of both upper and lower leaf surfaces is important, and frequent applications are warranted. Btk is a microbial insecticide and is most effective when caterpillars are young as larger (older) caterpillars are more difficult to manage because they need to consume more plant material before they are negatively affected (refer to “How to properly use Btk” in the August 2018 issue of Produce Grower for more information). Therefore, in order to reduce damage from large caterpillars that are less susceptible to insecticides, hand-pick and place caterpillars into a container of soapy water.

Raymond is a professor and extension specialist in horticultural entomology/plant protection in the Department of Entomology at Kansas State University. His research and extension program involves plant protection in greenhouses, nurseries, landscapes, conservatories and vegetables and fruits. rcloyd@ksu.edu or 785-532-4750