Imported Cabbageworm

Host Plants

This common garden pest is most attracted to the mustard and cabbage plant families. The latter, also known as the brassica family, includes cabbage, broccoli, kale, collard greens, brussels sprouts, cauliflower, mustard greens, and turnip greens.

Regions impacted

Found throughout North America and Europe.

Description

• Cabbage worms are one of the most common pests in the garden. The adult cabbageworm is an off-white butterfly with one or two grayish-black spots per wing (one for male; two for female) and a wing span of about 2 inches. These white butterflies are often referred to as “cabbage whites” or “cabbage moths”, although they are not technically moths at all.
• Cabbage whites and their progeny, cabbage worms, are present in gardens from early spring to late fall. The cabbage whites feed on nectar from flowers, but as they flit around the garden, they are laying eggs for the future destructive cabbage worms, the larvae of the cabbage whites.
• The larvae or cabbage worms are velvety green caterpillars, about 1¼-inch in length, with a fine yellow stripe down the back. Cabbage worms feed on foliage, particularly that of the brassica family (broccoli, cabbage, etc.).
• Cabbage worms can be confused with a similar caterpillar, the cabbage looper, which is usually skinnier and moves in an “inch-worm” fashion (raising and lowering their bodies as they move).
• Eggs are white or yellow and oblong in shape; they are usually found on the underside of leaves by themselves. The eggs resemble those of the helpful ladybug, which are, however, found in clusters.
• If and when going “egg hunting”, spare those of the garden-friendly ladybug.

Life Cycle

• Adults emerge from overwintering pupae in early spring to lay eggs. The female cabbage white seeks out plants from the brassica family, such as cabbage, mustard, broccoli, and kale, laying her eggs on the undersides of leaves.
• Larvae or cabbage worms hatch two to three weeks later. Larvae feed on the foliage for 2 to 3 weeks, then drop to the ground to pupate in or on the soil surface.
• Adult cabbage whites emerge in 1 to 2 weeks.
• There can be as many as three to five overlapping generations per year.

Damage and Detection

• As the cabbage worms emerge from their eggs, they start to feed on the surrounding foliage creating increasingly larger holes in the leaves.
• Some cabbage worm damage can be cosmetic, but if left undeterred, they can reduce plants to stems and, at the extreme, demolish leaves and plants as the caterpillars grow in size and population.
• Their fecal matter, or frass, can also stain and contaminate the produce. The caterpillars will continue to eat and grow for several weeks until they pupate.
• Cabbage white butterflies and cabbage worms are present in gardens from early spring to late fall, and several generations occur each season.
• With co-existing generations, numbers can build toward the season’s end, so gardeners must stay on guard the entire growing season to prevent cabbage worm damage to crops.

Prevention and Control

Manual Removal

• Manually squishing or removing the eggs and pests when you see them is one of the most effective ways to manage the population – if you can deal with it!
• To reduce damage from cabbage worms, inspect your plants frequently – once or twice per week.
• Cabbage worms and their eggs are most often found on the underside of leaves or tucked in the new growth at the plant’s center.
• In addition to holes in leaves, the frass or excrement that they leave behind is also a key indicator of cabbage worm presence.

Barriers or Row Covers

• Prevent egg-laying on your plants by creating a barrier around vegetable plants as soon as they are planted.
• A tunnel-like row of simple hoops covered with protective fabric (like netting) can be very effective.
• Install hoops made from PVC piping, metal, or bamboo, ensuring the hoops are high enough so plants will not touch them when fully grown. Secure hoop ends by pushing them deep into the ground.
• When installing the netting, allow at least 6 inches of fabric to drape on the ground on all sides, and place rocks or other heavy objects on top of the excess fabric to keep it in place.
• Remove the netting when flowers form and pollination begins
• Row covers designed in this way make it impossible for the cabbage white butterfly to access your plants and lay her eggs and also act as a deterrent to squirrels, rabbits, birds, etc.

Plant Purple & Red Varieties

• Cabbage worms are seemingly less attracted to red and purple vegetables, perhaps because the green pests cannot blend into the backdrop and feel exposed.
• Whatever the reason, they eschew red-leafed cabbage, making it a good addition to the garden.

Companion Planting and Trap Crops

• Thyme, dill, oregano, lavender, onions, garlic, and marigolds are said to deter cabbage whites and can be interplanted with the main crop.
• Some plants can serve as a “trap crop” to attract cabbage worms away from your primary crop. Cabbage worms are attracted to mustard plants, so planting mustard near more valuable plants can lure cabbage worms away.
• Be sure to periodically remove infested trap crop plants or manually remove and kill the cabbage worms from the trap crops.

Beneficial Insects

• Parasitic wasps (which don’t sting) lay their eggs inside or on top of the cabbage worm and their pupae. Once their eggs hatch, the wasp larvae feed on the host caterpillar, killing it.
• These beneficial insects are available by mail order from various providers.

Neem Oil Spray

• Neem, a plant-based oil, can act as a deterrent to cabbage worms. A routine spray of your garden periodically can repel these pests; however, if a plant is already infested, neem oil will not typically kill cabbage worms.

Bacillus Thuringiensis (Bt)

• Spray Bacillus thuringiensis (Bt for short) is an organic pesticide that can be utilized to kill off a variety of pests in the garden. It is only toxic to the larvae of butterflies and moths and not to birds or other mammals, making it the best way to organically, but effectively and easily, get rid of cabbage worms.