Diamondback Moth
Plutella xylostella (Linnaeus), Yponomeutidae, LEPIDOPTERA


DESCRIPTION

Adult - This grayish-brown moth has narrow forewings, conspicuously fringed hind wings, and an 18 mm wingspan. When at rest, the wings of the male come together to form a line of white or pale yellow diamonds down the middle of the back.

Egg - The minute round egg is pale yellow.

Larva - Tapering slightly at both ends, this pale green larva with a black head and scattered black hairs reaches a length of 7 mm when mature. It wriggles rapidly when disturbed, often dropping from the plant and hanging by a silk-like thread.

Pupa - The yellowish pupa is enclosed within a loosely spun, gauze-like cocoon measuring about 7.5 mm in length.


BIOLOGY

Distribution - A native of Europe, the diamondback moth can be found throughout the U.S. and in all areas of the world where cole crops are grown. It can be a problem in greenhouses also.

Host Plants - The diamondback moth is a pest of practically all crucifers, including cabbage, broccoli, cauliflower, collards, kale, brussels sprouts, kohlrabi, turnip, radish, mustard, and watercress.

Damage - Diamondback moth larvae feed on all plant parts, but prefer the undersides of older leaves, crevices between loose leaves, and young buds. They eat small holes in leaves and buds, or feed superficially leaving slight perforations instead of holes. When populations remain low, these small caterpillars cause little damage; however, in large numbers they are particularly injurious to young plants. Heavy feeding on buds may cause the marketable portion of the plant to fail to develop properly.

Life History - Diamondback moths overwinter as adults among field debris of crucifer crops. In spring, eggs are laid, singly or in groups of two or three on foliage. Larvae, which hatch from eggs a few days later, feed for about 10 days during warm weather and a month during cool seasons. Larvae first feed as leafminers but soon emerge and infest the undersides of leaves. Once mature, larvae spin loose cocoons which remain attached to lower leaf surfaces. After a 2-week pupal period, a new generation of moths emerge. In temperate regions, the diamondback moth has 2 to 6 or more generations each year. Five or 6 generations per year are common in North Carolina.


CONTROL

Since these moths overwinter in the field, destroying or plowing under crop debris is a recommended cultural practice. Planting resistant varieties also reduces infestation. The following crucifer varieties are less attractive to diamondback moth larvae: Michihli Chinese and Mammoth Red Rock (cabbage); Southern Giant Curled (mustard); Seven Top and Purple Top White Globe (turnip); Vates (kale); and Cherry Belle, White Icicle, Globemaster, and Champion (radish).

Diamondback moth caterpillars are controlled by the same insecticides used against other caterpillars on crucifers. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemical Manual.

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