Autumn is cabbage season. Whether you grow them to eat or plant them as ornamentals to add color to your landscape, cabbages and kale thrive in the chilly nights and cool days of fall. While walking through a row of kale the other day, I noticed ragged holes and missing margins on several leaves. Closer inspection revealed scads of beautiful bristly green caterpillars beneath the leaves. Nearby, adults of these cabbage worms dashed about rows of kale and broccoli searching for mates and depositing eggs beneath leaves.
Adults of the imported cabbage worm are called cabbage whites. They arrived in our country from Europe in the 1860’s. Cabbage whites are among the first butterflies seen each spring when they emerge from chrysalises that provide refuge during the winter. In addition to their fondness for kale, broccoli, and cabbage, they deposit eggs on cauliflower, Brussels sprouts, turnips, radishes, and weeds in the mustard family. Several generations of this butterfly develop annually throughout much of their range in the United States from Canada to Mexico and coast to coast.
Cabbage white butterflies adore autumn perennials like this lantana.
Although I find the antics of the caterpillars and butterflies entertaining, some find the presence of these worms on their greens unpleasant. If you grow just a few cabbages, broccoli, or cauliflower, regular inspection of the plants and removal of the caterpillars can help reduce damage. Mother Nature’s army of parasitic wasps and predatory bugs greatly reduce the legions of cabbage worms when gardens and landscapes are diverse and sustainable. Some gardeners enshroud rows of cabbage and broccoli with netting to prevent cabbage whites from reaching leaves to lay their eggs – no eggs, no caterpillars, and no damage. Some varieties of cabbage, including Early Globe, Red Acre, and Round Dutch, are reported to show some resistance to cabbage worms.
Many insecticides are available to control caterpillars including cabbage worms. Among the most environmentally friendly are products containing the microbial biological control agent, Bacillus thuringiensis, also known as Bt. Bt products are simply mixed with water and sprayed on the plant. As the caterpillar eats, Bt is ingested. This microbe and proteins produced by it destroy vital cells inside the gut of the caterpillar. The result is gut paralysis and starvation – a slow and painful death.The imported cabbage worm is not without its own defensive tricks. The hairs lining its body are glandular and produce secretions repellent to potential predators like ants. This may be part of the reason for the remarkable success of this alien species here in America.
The imported cabbage worm is not without its own defensive tricks. The hairs lining its body are glandular and produce secretions repellent to potential predators like ants. This may be part of the reason for the remarkable success of this alien species here in America.
Tiny cabbage worms make tiny holes in cabbage leaves of course.