CABBAGE LOOPERS IN YOUR GARDEN
COMMON NAME: Cabbage looper or inchworm.
SCIENTIFIC NAME: Trichoplusia ni
DESCRIPTION:
Adults - Small, mottled-brown moths with a silvery spot on the forewings. The wing-span is about 1 1/2 inches and they fly at night.
Pupae - A green or brown pupae can be found wrapped in a white silken cocoon attached to a plant leaf.
Larvae - A large (up to 1 1/2 inch) light green caterpillar with a light green stripe down its back. It gets the name "inchworm" from its looping-type movement from place to place.
EGGS - The round, greenish-white eggs are laid singly, usually on the upper surface of leaves.
LIFE CYCLE: The cabbage looper overwinters in the pupal stage in leaf litter. In the spring, the adult emerges and lays eggs on a host plant. In a few days the small green caterpillar hatches and starts to feed voraciously. When it reaches full size, the larvae then attaches itself to the underside of a leaf, spins a silk-like cocoon and pupates. In about two weeks the new adult will emerge and fly away seeking to mate and lay its eggs. This cycle will repeat itself approximately every three weeks throughout the summer. In the fall, the last generation will overwinter as pupae.
HOST PLANTS: Beans, broccoli, Brussels sprouts, cabbage, cauliflower, celery, collards, kale, kohlrabi, lettuce, parsley, peas, potatoes, radish, rutabagas, spinach, tomatoes, and turnips.
TIME OF THE YEAR: From spring (late April or early May) until late fall.
WHAT TO LOOK FOR: The first sign of cabbage loopers is usually holes eaten in the leaves of your plants. It may be small holes, but you will most likely see large, ragged pieces missing or even entire leaves gone. You may find small brown pellets or droppings on what remains of the foliage. Closely inspect the leaves for eggs, pupae, or larvae of the pest.
PROBLEMS AND DAMAGE: Plants can be virtually defoliated in a very short period of time. This not only destroys plant parts you may have been planning to eat, but if enough is eaten, the whole plant will die. Even if the plant survives, it will be weakened and more susceptible to other pests and diseases.
CULTURAL CONTROLS: Practice crop rotation (3-5 year cycles) and plant resistant varieties when available. Clean up garden debris to destroy overwintering habitat. Use "timed planting" and plan your crop so that your most vulnerable plants (young, with few leaves) are not exposed to the pest. Start your plants inside so that you can transplant large seedlings outside. If damage is noted, remove the leaf or carefully cut away the chewed area. This way, if you notice more holes later, you will know that you still have the pest present rather than thinking that it is still the same damage from before.
COMPANION PLANTING AND REPELLENTS: Marigolds, garlic, onions, sage, hyssop, rosemary, tansy, hot peppers, and thyme have all been used to keep the loopers at bay. You can also make a spray from them (alone or in combination), with onions, garlic, and hot pepper solutions reported as working the best.
TRAP PLANTS: Plantings of amaranth or celery close by can sometimes give you warning that the loopers are in the area as the pest often attacks them first.
MECHANICAL CONTROLS: The best defense may be to cover your crop with an agricultural fleece product (Remay, etc.). If the moth can't land to lay her eggs then there will not be any caterpillars eating your plants. Be very careful to secure the edges and leave enough extra cloth for the plants to grow. You may have to remove the cover later if it gets too hot under there. Spraying your plants with a hard stream of water or soapy water may dislodge the pests so you can pick them up and destroy them. Hand picking and squashing them is very effective. Diatomaceous Earth (DE) or salt sprinkled on the creatures will dry them up. Use "bug lights" or light traps to get the adults.
NATURAL CONTROLS: Cabbage loopers and other caterpillars are a favorite meal for lacewings, ladybugs, lizards, toads, and all sorts of birds. Trichogramma wasps parasitize their eggs and destroy them. If you find any loopers that appear chalky white and almost dead, collect them and make "bug juice" out of them. They have a disease called Nuclear Polyhedrosis Virus (NPV). A single spraying of this virus may be enough to control your cabbage looper population for the entire season! Unfortunately, it is not yet available commercially. Bacillus thuringiensis (BT) is a commercially available bacterium that will kill caterpillars and is harmless to other creatures. Start spraying when you see the first damage and every two weeks thereafter. You can even use it as a preventive and start spraying about one week after transplanting if you have had problems with this pest in the past.
BIOLOGICAL INSECTICIDES: These are not totally harmless, but used correctly, they can be easier on the environment than some other methods. Use an insecticidal soap (such as Safers), pyrethrum, ryania, sabadilla, or rotenone. Spray in the evening when the honey bees are not around, and follow directions carefully.
CHEMICAL CONTROLS: Call you County Extension Agent or the staff for current recommendations. Check at your favorite garden supply store or nursery to see what they have available. Remember to check the label to make sure that the cabbage looper is a listed target pest and FOLLOW THE DIRECTIONS EXACTLY! When it comes to pesticides, more is NOT better!! Wear protective clothing, watch out for non-target plants, pets, children, and other living things. Wash your skin and clothing after application, and take care not to get the substance into your eyes, mouth, or breathing passages.