Curse of the Cabbage Looper

The little green cabbage looper (Trichoplusia ni) looks harmless enough. The larval form of the cabbage looper moth, a brown, nondescript insect that more closely resembles bird droppings than moths, cabbage looper caterpillars cause serious damage to vegetable crops.

Plants Cabbage Loopers Eat

A long list of plants decimated by cabbage loopers include, of course, cabbage, broccoli, cauliflower, Chinese cabbage, collards, kale, mustard, radish, rutabaga, turnip and watercress.

Other plants affected by the animal are cotton, potatoes, tomatoes, sweet peas, snap beans, spinach, squash, sweet potatoes and watermelon. The loopers have also been known to attack chrysanthemums, hollyhocks and snap dragons.

How Loopers Damage Plants

The loopers damage plants by feeding on leaf edges in early stages of their growth, the leaf centers in later states and finally on the tender parts of the plant’s center in the last stages. Loopers will bore right into the developing heads on cabbage.

Consuming several times their weight every day, a heavy infestation of larvae can cause significant damage to plants in a week.

Control of Cabbage Loopers

Perhaps the best, least costly and easiest way of getting rid of cabbage loopes is to pick them off the plants. Although first-time gardeners may have difficulty finding the larvae on an infected plant, practice and careful observation proves successful.

Cabbage loopers do have enemies. Wasps and tachinid parasitic insects will lay eggs on the larvae, or they will sting the larva, bringing it back to a nest as food for their own larvae. Although they are deadly to cabbage loopers, there are not enough of them around to significantly affect the population.

Baccillus thuringiensis (BT) is a bacterium that gets into the gut of the larva, sickens it, and eventually kills it within a few days. BT occurs naturally in the soil, and is considered harmless to humans, animals and beneficial insects.

BT can be purchased from gardening centers and nurseries under a variety of brand names. While BT is not harmful to the environment, it will not kill the larvae immediately. It will instead sicken the looper which will die in a few days. And while it’s not damaging to humans, vegetables shouldn’t be eaten right after they have been sprayed with BT. Wait a few days and then thoroughly wash them.

Adult Cabbage Looper Moth

The adults feed on nectar from goldenrod, sunflower and clover, among others. The are nocturnal or semi-nocturnal. The may also be active on cloudy days. The females lay between 300 and 600 eggs in one evening. The eggs are the shape of a half ball, with the flat side resting against the surface of a leaf.

Native to North America, it’s found just about everywhere in the United States, Canada and Mexico.