Teri H. Briggs, Geoff W. Zehnder, and James B. Witt

VARIOUS MOTH LARVAE CAN CAUSE SERIOUS DAMAGE to cabbage grown in the South, but concerns over synthetic pesticide residues in food and the environment prompt commercial vegetable growers and home gardeners to seek natural pest control alternatives. Organic gardening literature is rich with anecdotal evidence for the effectiveness of organic insecticides. However, few formal studies have been done to evaluate these materials.

An AAES experiment compared a standard synthetic pyrethroid insecticide with some commonly available organic insecticides for control of diamondback moth and cabbage looper larvae, or worms, on cabbage. Results indicate that the organic insecticides, which are composed of natural, non-polluting materials, do not provide the same high level of worm control as pyrethroids. But they do demonstrate moderate to good activity against the worms and can acceptably control worm feeding damage.

Adult female diamondback and cabbage looper moths lay eggs on cabbage plants. The hatching worms feed on the outer leaves and heads, causing defoliation and reduction in grade or marketability of cabbage.

	Obvious signs of cabbage looper feeding include feeding damage, the physical appearance of the larva, and the presence of larva frass.
	The larva is the stage of the diamondback moth that causes feeding damage.

Fortuna cabbage was transplanted on March 18 at the E.V. Smith Research Center in Shorter. Treatment rows were sprayed on a weekly schedule until harvest using a backpack sprayer with three hollowcone nozzles per row. Ivory Snow liquid laundry soap (at a rate of 0.5 milliliter [ml], or six drops per two-liter bottle) was added to the spray mixture in all spray treatments to enhance even wetting of the cabbage leaves and avoid large drops of spray on the leaves. Spray volume was 55 gallons per acre at a pressure of 40 pounds per square inch. Worm counts were recorded weekly, and a visual damage rating was assigned at harvest on June 13. The table lists the seven materials evaluated in the study.

Karate, applied at a rate of 0.75 ml per two-liter bottle, was used as the standard synthetic pyrethroid insecticide. (Note: a gallon is 3.8 liters, and an ounce is 59 ml.) Commonly used by commercial growers to control moth larvae, this product contains 13.1 % lambda-cyhalothrin, the active ingredient.

Garlic Barrier, a 100% garlic-juice product advertised as an insect repellent, was obtained from GRAB-IT Enterprises in Jackson, Ala. This product enters the plants through stomata (breathing pores in the leaves) and moves systemically throughout the plant. As recommended by the manufacturer, Gatlic Barrier was mixed with an equal amount of fish oil (exact composition unknown). Garlic barrier and fish oil were each applied at the rate of 200 ml per two-liter bottle.

The primary ingredient (83.2%) in Organic Plus, obtained from Organic Plus, Inc., of San Antonio, is diatomaceous earth, or finely ground fossilized shells of tiny aquatic organisms called diatoms. These microscopic pieces of silica can pierce the worm cuticle on contact, resulting in loss of body fluids and ultimate death. Organic Plus also contains 0.2% pyrethrins, a natural insecticide from chrysanthemum plants, and 1.1% piperonyl butoxide, a compound added to block insect resistance to the pyrethrin. Organic Plus was applied at 30 grams per two-liter bottle. (Note: one ounce is 28 grams.)

Align, manufactured by Agri-Dyne Technologies of Salt Lake City, Utah, is a botanical insecticide containing 3% azadirachtin, a natural insecticide obtained from the tropical neem tree. Azadirachtin has activity against a wide variety of insect species, including moth larvae, but has no reported adverse effects on mammals. Align was applied at 4.4 ml per two-liter bottle.

The active ingredient in Javelin WG, manufactured by Sandoz Crop Protection of Des Plaines, Ill., is a toxin obtained from a bacterium, Bacillus thuringiensis variety kurstaki. The toxin is active only against moth larvae; it acts as a stomach poison that must be consumed by the worms for activity to occur. Javelin WG was applied at the rate of 3.8 grams per two-liter bottle.

Ground red pepper, obtained at a local super market, has also been reported as an insect repellent. The spice was applied at the rate of one
tablespoon per two-liter bottle.

The Ivory Snow liquid laundry detergent used in this test was obtained from a local supermarket and applied at the rate of 20 ml per two-liter bottle. The 0.5 ml of Ivory that all other treatments contained does not affect the insects, but the 20 ml concentration is harmful to them. Insecticidal soaps act on contact against soft-bodied insects by degrading the insect cuticle. They also may suffocate the insect by blocking spiracle openings.

Diamondback moth numbers reached neatly five per plant on May 30, and peak cabbage looper numbers (2.4 per plant) were recorded on June 4. Numbers of diamondback moth larvae were highest in the nontreated control on May 21 and 30. Diamondback larvae counts were significantly lower in all treatments, compared with the control, on these dates.

The season average diamondback counts indicated that Karate provided the best control. The organic products Garlic Barrier and Organic Plus provided the next highest level of protection. Align and Javelin WG were slightly less effective than these products in reducing diamondback numbers. Red pepper and Ivory soap had the least effect on the diamondback population but were still more active than the control. All treatments, except red pepper, provided a significant level of cabbage looper control on June 4, when worm numbers were at their highest.

Damage ratings reflected the degree of worm control resulting from the treatments. Cabbage plants in the Karate treatment exhibited the least worm damage, while plants in the red pepper treatment exhibited the most. However, the average worm damage ratings in all of the organic treatments were below 4, indicating that most of the damage occurred on the outer leaves, and was not sufficient to render the plant unmarketable. Of the organic materials, Javelin WG and Align were best at controlling worm damage, followed closely by Garlic Barrier. While red pepper was one of the least effective treatments, it did provide a surprising level of control. Sprays were applied at seven-day intervals, and the red pepper was not expected to have long residual activity, but it still offered moderate control of worms and damage.

Of all the treatments, the synthetic pesticide Karate gave the best control of cabbage worms. However, the organic materials are useful for home gardeners and commercial producers who want to avoid synthetic chemical residues and can accept some insect damage on their cabbages.

Briggs is a Research Technician, and Zehnder is an Associate Professor in the Department of Entomology. Witt is Superintendent of the E.V Smith Research Center Horticulture Unit.