Vegetable Insect Note 11
The foliage of broccoli, cabbage, cauliflower, collards and related crops is damaged by the larvae ("worms") of this introduced pest from Europe. This most serious pest of crucifers grown throughout the world appears to be on the increase on collards and cabbage in North Carolina, and the development of resistance for some N.C. populations has resulted in major concern by growers.
Diamondback moths are about 1/3 inch long, gray in color, have a wingspread of less than one inch, and move rapidly when disturbed.
Males have 3 yellowish diamond-shaped markings on the back when the wings are folded together. Female moths lay eggs either singly
or in groups of two or three on the leaves or stalk near the terminal
bud. Eggs are small, spherical, yellowish to white, and hatch in 5 to 6 days, depending on temperature.
Larvae are light
green, slightly tapered at each end, and are covered with tiny, erect black hairs. When full-grown they are about 1/3 inch long.
They wiggle rapidly when disturbed, often dropping from the plant and hanging by silken
threads. Larvae feed on all parts of the host plant, but they prefer places around the
bud.
They may eat small holes in leaves, or feed superficially, leaving a thin layer of
tissue intact, creating a windowpane effect. Such feeding may damage the bud of a young plant so that
the head or other marketable part will not develop properly. The larval stage consists of 4 instars and lasts 10 to 30 days
depending upon temperature, food supply, and other factors. Pupae are encased in loosely woven gauzelike cocoons
fastened to the leaves or other parts of host plants. This stage lasts 7 to 10 days in summer. There are 5 to 6 generations
per year in North Carolina. The pest apparently overwinters in the adult stage protected by debris in the field. Hence, early
crop destruction could reduce overwintering populations of diamondback moths.
For more information, including more color photos and line drawings, see Vegetable Insect Note 12: Cabbage Worm Complex.
In recent years, failures with insecticidal control of diamondback moth have been reported. This insect is becoming increasingly difficult to control, especially where cruciferous crops (cabbage, collards, greens, etc.) are grown continuously or in close proximity. Rotate as far as possible from the previous crop and alternate chemicals used. Be sure to destroy planting at completion of harvest.
Diamondback larval populations should be monitored weekly up to head formation. Adults can be monitored with sex pheremone traps. Control recommendations should be based on trap and larval counts, plant growth stage, level of resistance, weather and natural enemies.
When spraying a commercial acreage, a high pressure (200+ psi) sprayer with 3 hollow cone nozzles per row is recommended. This, plus a spreader-sticker added to the spray solution, will ensure complete coverage of allareas of the plants, especially the undersides of leaves where larvae are most often found. For commercial plantings, see the North Carolina Agricultural Chemicals Manual. The following table is a summary of recommendations for broccoli, cabbage, and collards in North Carolina home gardens.
| Insecticide & Formulation | Amount of Formulation/Acre | Minimum Interval (Days) to Harvest | ||
|---|---|---|---|---|
| Bacillus thuringiensis | ||||
| several | (see label) | |||
| carbaryl (Sevin) | ||||
| 50 WP | 4 tbsp | 3: broccoli, cabbage; 14: collards | ||
| 80 WP | 2-1/2 tbsp | 3; 14 | ||
| 4 XLR | 2 tsp | 3; 14 | ||
| 5D | (see label) | 3; 14 | ||
| naled (Dibrom) | ||||
| 8EC | 2 tsp | 1: broccoli, cabbage; 4: collards | ||
Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data.
Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact your county North Carolina Cooperative Extension Service agent.
For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service personnel.
Published by North Carolina Cooperative Extension Service
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Web page last updated on 09 May 1996 by M.J. Munster