Beet Armyworm
Spodoptera exigua (Hubner), Noctuidae, LEPIDOPTERA


DESCRIPTION

Adult - The beet armyworm moth has a wingspan of 25 to 32 mm. Its forewings are mottled gray or brown with a pale spot near the center of each wing. Its hind wings are white with dark veins and have a fringe-like border.

Egg - The white to pink, ribbed egg is roughly spherical in shape and slightly peaked on top. Scales and hairs from the moth give the egg cluster a gray, fuzzy appearance.

Larva - This green or black caterpillar has a dark head, five pairs of prolegs, and sometimes three lightly colored stripes running the length of the body. On the second segment behind the head, there is a small black spot on each side of the body. This spot usually becomes visible to the field observer when the caterpillar reaches 7 to 8 mm long; however, the spot may be difficult to see on a dark caterpillar. About 1 mm long when newly emerged, a larva may be 25 to 30 mm long when fully grown.

Pupa - About 15 to 20 mm long, the pupa is light brown with dark brown margins along the abdominal segments.


BIOLOGY

Distribution - Native to the Orient and introduced into this country around 1875, the beet armyworm is now common throughout the southern and western U.S. It occurs northward into Montana.

Host Plants - The beet armyworm infests many weeds, trees, grasses, legumes, truck crops, and field crops. In various states, it is of economic concern upon asparagus, cotton, corn, soybean, tobacco, alfalfa, table and sugar beets, pepper, tomato, potato, onion, pea, sunflower, and citrus. In addition, plantain, lambsquarters and redroot pigweed are wild hosts which are attractive to beet armyworms.

Damage - Early instar beet armyworms most frequently damage the young terminal growth. Profuse silk webbing may give infested plants a shiny appearance. Later instars do not feed gregariously and the production of webbing is discontinued.

Life History - In warm areas, such as Florida and California, the beet armyworm moths may be found year-round. In less tropical areas, these insects can survive the winter as pupae in the upper 6 cm of the soil. The extent of the overwintering distribution, however, has not been adequately studied. This insect is not believed to overwinter as far north as Kentucky or North Carolina. Vegetable crops in North Carolina apparently become infested by migrating moths. In spring, soon after mating, fertilized females begin laying eggs in clusters of about 80. Each female can deposit approximately 600 eggs over a 3- to 7-day period. Moths die 4 to 10 days after emerging from pupae.

Eggs hatch in 2 to 3 days. The newly emerged larvae spin loose webs around themselves, feed gregariously on the remains of the egg mass, and then attack plant foliage. They eventually scatter to different parts of the plant. After feeding 1 to 3 weeks, larvae (fifth instars) pupate within loose cocoons composed of soil particles, leaf fragments and trash. About 1 week later moths emerge. The entire life cycle requires 4 to 5 weeks. Several generations occur each year.


CONTROL

The beet armyworm has few effective parasites, diseases, or predators to lower its population. Effective chemicals for beet armyworm control are available to the commercial vegetable producer or licensed applicator. Most chemicals cleared for home garden use will not control this pest adequately. For up-to-date recommendations, consult the current North Carolina Agricultural Chemicals Manual.

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