Grassworm

Common: Fall Armyworm/Grassworm

Scientific: Spodoptera frugiperda

Crop Hosts: Corn, sorghum and other grasses are preferred but it will attack a wide range of legumes and vegetables.

Identification and Life Cycle: This is a tropical insect that cannot live though the winter if the ground freezes hard. In the spring, swarms of adults fly northward and deposit eggs on green plants. They have a wingspan of 1 1/2 inches and are grayish-white in color. Each female lays 1,000 eggs and small larvae emerge in a few days. They feed near the ground. The full-grown larvae have yellowish-white hair lines down the back and can be distinguished from the true armyworm by the more prominent white inverted Y on the front of the head. They dig into the ground pupate and the adult emerges in about 14 days. In the south there may be 5 to 10 generations.

Geographical Distribution: Fall armyworm is in continuous residence in the Gulf Coast states and Florida. They can migrate as far north as Montana and Michigan in the summer.

Damage and Treatment: The young larvae first feed near the ground and can go unnoticed. When abundant, the caterpillars eat all the food on hand and then start to crawl in great armies into adjoining fields. Gardens can be invaded and consumed in a few nights.

Treatment should be made when insect populations and/or damage levels reach economic thresholds. Refer to local University Extension Pest Management Guidelines for specific state thresholds.