Beet Armyworm - Cotton Insect Management

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Insect Management
Cotton Insect Management
Beet Armyworm - Spodoptera exigua (Hubner)

Description

The stages of development of the beet armyworm are the egg, larva, pupa, and adult. The eggs are laid in masses of about 80 to 150 eggs on the upper and lower surface of leaves. Egg mass size is usually about 1/2 the size of a dime. The eggs are covered with a gray to green colored fibrous substance deposited by the female moth. The individual eggs are green in color.

The larvae range in color from light green to dark olive green or black. The average is about 1-1 /4 inches in length at maturity. On either side of the body is a wide black stripe bordered by yellow. A characteristic small black spot is on each side above the second pair of true legs. This dot is difficult to see on darker colored larvae. The body is usually green and has five pair of prolegs. The pupa is brown in color and found underground.

The adult moth is a mottled gray color with a pink or pinkish white dot in the center of the front wing. The hind wings are white with a dark margin. The wingspan averages about 1-1 /4 inches.

Adult	Larva
Egg Mass

Biology

Diagram showing the life cycle of the Beet Armyworm. The egg mass hatches in 2 to 3 days. Larvae feed about 18 to 20 days on the foliage, squares, and bolls. The complete life cycle is about 27 days. Several natural control agents are a factor in managing the beet armyworm population including predators, parasites, and diseases. Only the larval stage causes damage to cotton. Host plants for the beet armyworm include cotton, soybean, cocklebur, pigweed, and morningglory. Beet armyworm tend to prefer pigweed as a host and infestations will usually be found first on or around this host plant.

Damage

The young beet armyworm larvae feed primarily on foliage leaving a skeletonized effect. As the larvae gets older, feeding includes the foliage, squares, bloom, and bolls. Beet armyworm are gregarious and usually are found in groups of 30 to 200 or more. The overall larval feeding results in cotton plants appearing ragged looking and the damage may be seen from a short distance. Infestations of larvae may be spotty occurring only in certain areas of the field.

Scouting

While walking the fields, watch for egg masses by examining the upper and lower leaf surfaces. Egg masses are easily seen by tilting the entire plant over and looking at the underside of all the leaves at once. Observe the number of eggs and larvae in the field and classify according to the criteria that follows.

Eggs

None - No egg masses found.
Light - A few egg masses (1 to 4) found per 56 row feet.
Medium - Several egg masses (5 to 15) found per 56 row feet.
Heavy - Greater than 15 egg masses found per 56 row feet.

Larvae

None - No larvae found.
Light - An occasional larvae found or up to 4 colonies of larvae found (i.e. up to 4 groups of 30 to 200 larvae. Each group will be on about 10 row feet of cotton).
Medium - Several colonies or groups of larvae found scattered throughout the field with feeding damage to foliage, squares, and bolls (5-15 groups of 30 to 200 larvae).
Heavy - Many colonies or groups of larvae found throughout the field with extensive feeding on foliage, squares, and bolls. (Greater than 15 groups of 30 to 200 larvae. Each group will be on about 10 to 15 row feet of cotton.)

Back to Cotton Insect Management

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Insect Management Cotton Insect Management Beet Armyworm - Spodoptera exigua (Hubner)

Insect Management
Cotton Insect Management
Beet Armyworm - Spodoptera exigua (Hubner)