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Cabbage Looper

Closer Look Of The Cabbage LooperThe cabbage looper is a 1 to 2 inch long velvety green moth larva caterpillar, with white lines running down its back. The looper mostly attacks the leaves of cabbage, broccoli, cauliflower and Brussels sprouts (cole crops), but some other plants to a lesser extent. The insect gets its name by doubling up, or loping (raising its back in the air) as it moves. They tend to be more destructive than either the imported cabbageworm or the diamondback moth larvae and are said to be more difficult to eradicate. You can tell their presence by looking for holes in the leaves or dark green droppings (larva excrement). If left unchecked, they will invade the cabbage head, making it unfit for consumption, the same being true for broccoli and cauliflower.

The green loopers use camouflage as their main defense, so they can be hard to see, and the newborn have somewhat clear bodies, making them even more difficult. The young nibble on the underside of the leaf, but don’t do much damage, while the more mature ones eat right through, creating holes and causing the worst problems. They ‘poop’ all over the place, making a real mess, so you will want to eliminate this pest as it appears, which will be late spring, all summer and into early fall. It is worth mentioning that loopers only feed in the caterpillar (larva) stage of their lives, not the other stages (adult stage, egg stage or pupae stage).

Adult

Cabbage Looper Adult MothThe adult is a mottled grayish-brown moth with a wingspan of about 1 1/2”, which is normally nocturnal, but can sometimes be seen during the day resting on the bottom side of leaves. Looking closely, you will see two small silvery-white figure 8’s or ‘Y’ marks in the middle of each wing. If you see these silver marks, you are looking at the cabbage looper moth.


Eggs

Cabbage Looper EggsAfter mating, the female moths live about 2 weeks, but during their short life lay between 200-400 small eggs on the underside of cabbage leaves. The eggs are usually in the form of a sticky mass and can be white, pale green or pale yellow in color, and which hatch in only a few days. If you see these eggs, spray them off with water or a solution of insecticidal soap and water.


Larvae

Cabbage Looper LarvaeYoung loopers, which are known as larvae, are about 1/4” long, but quickly grow to their full 1 1/2”size, eating everything in sight and living for about 3 weeks. This is their most destructive stage when they do the most damage, eating holes in the green leaves of your crops, leaving their droppings all over the place.


Pupa

Cabbage Looper PupaThen they form a cocoon, normally on the underside of the leaves or in nearby brush piles, and begin to pupate. The loopers enclose themselves in a white thread-like cocoon that’s about 3/4” long, the caterpillars turning copper brown in several days. What’s happening here is that the caterpillar is metamorphosing from a caterpillar larva into an adult moth.

After about 10 days in the cocoon, they emerge as winged adult moths and the life cycle begins all over again (mating, laying eggs, etc). Depending upon the temperature and weather, as many as three or four generations of loopers can be produced during the summer growing season, averaging about one generation every three to four weeks. So the pest will attack your garden crops from late spring, all summer long and into early fall, a good frost being needed to kill them.


Vegetables That Cabbage Loopers Like To Eat

Beets Cauliflower Lettuce Potatoes
Broccoli Chinese cabbage Lima beans Radishes
Brussels sprouts Collards Parsley Snap beans
Cabbage Cucumbers Parsnip Spinach
Cantaloupe Kale Peppers Squash

Control

Using the insecticide BT will normally control young cabbage loopers, but is less effective with mature adults, being aware that BT won’t kill them for several days, but the loopers should stop eating right away. A good thing about BT is that it is not harmful to bees and is considered a natural, organic substance (approved by organic gardeners). Apply BTK (the kurstaki variation of BT) in early evening when the winds have died down and no bees or butterflies are present, as some studies suggest that BT can be harmful to Monarch butterflies. BT breaks down quickly, so its toxicity will be much less the next day. Remember that BT is only effective when an insect is in its larval (eating) stage, such as when the cabbage looper is in the caterpillar phase of its life. It does no good to apply BT to eggs, pupae or spray it on an adult moth. It is only effective against actively feeding caterpillar cabbage loopers. When you see young caterpillars, then spray, but not before they hatch from their eggs. Finally, if you spray loopers with BT (var. kurstaki), and they don’t stop eating and die after several days, it could be that your BT is old and no longer effective, a common problem with home gardeners. If this happens, purchase a fresh bottle of BT and try again.

Floating Row Cover Over The Cabbage Plants Hiding the cole crops under floating row covers (see picture at left) is an excellent means to preventing the adult moth from laying her eggs on your plants and not having to use any insecticides at all. Because loopers find it difficult to move about, the row covers will form an effective defense against them. This is our preferred defense. (See Bill's Projects for making your own row cover supports)

Sevin, Malathion and Diazinon are also effective but are much stronger insecticides. Pyrethrins or neem are less effective but are more natural and organic in nature, so try these second to BT. Finally, hand picking the loopers is feasible for small gardens, putting them in a small pail of water to drown. If you don’t want to touch the caterpillars, make a simple caterpillar picker.

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