How to Fight Common Pests of Cabbage and Other Brassicas

by Erin Marissa Russell

When you’re growing cabbages, broccoli, cauliflower, or kale, you’re likely to run up against the garden pests this article will teach you to fight: the ones that prey on brassicas. Brassicas are a school of vegetables that include bok choy, broccoli, broccoli rabe (also called broccoli raab or rapini), broccolini, Brussels sprouts, cabbage, cauliflower, collard greens, daikon, kale, kalettes , kohlrabi, mizuna, tatsoi, turnips and turnip greens, and wasabi. Read on to learn how to identify insects that target brassicas in your garden, what the damage they cause can look like, and what you should do to fight back against them.

Aphids

Several varieties of aphids can cause trouble in a garden full of brassicas. You may see the tiny nymph or adults, with or without wings, in a variety of colors. Crops show that aphids have been feeding on them with wrinkled or dried-up looking leaves that may be distorted in shape. When infestation is widespread, plants may not recover.

You can manually remove aphids by squirting them off the undersides of plant leaves with a high pressure hose or by squashing them individually. All-natural insecticide sprays, either over-the-counter or ones made with ingredients like garlic, onion, or neem oil, have been reported to beat out aphids. Some gardeners swear by half a teaspoon of liquid dish soap diluted in a quart of water and sprayed over plants. Be sure to remove the stumps of brassica vegetables from the ground after harvesting, as aphids can use the material left behind as a safe place to spend the winter.

Birds

Although the most common pests that come to mind for gardeners are often insects, plenty of gardens fall prey to birds, so it makes sense to protect against them. In addition to seeing the birds in your garden, you may also see damage that resembles the feeding of caterpillars. If birds descend when plants are young, the results can be severe. Some gardeners report birds eating up an entire planting of brassica seedlings in just one day. Cover netting is the simplest solution to protect a garden against birds as it will keep birds from being able to reach the plants. Gardeners should ensure that there are no sagging areas in the net that can give birds access to plants just by sitting on low spots in the netting.

Cabbage Centre Grub

Gardeners may encounter the cabbage centre grub in one of many stages. The eggs are oval-shaped and cream in color. Grubs lay them on young leaves or on the surface of the soil. You may also see cream-colored caterpillars with a reddish brown striped pattern or brown pupae hanging from webbing in the plants. The adults are moths with a mottled brown color. You’ll see evidence of the cabbage centre grub in areas where caterpillars have fed. In addition to missing young growth, the caterpillars show their presence with a sawdust-like byproduct called frass and in webbing within the plants. Floating row covers can prevent the airborne adults from being able to lay eggs on your young plants. Examining plants for the caterpillars and dropping them each by hand into a pail of soapy water is effective enough to spend the time doing it. The nontoxic biologic insecticide Bacillius thurengiensis (Bt) is also effective against caterpillar grubs, worms, and moths.

Cabbage Cluster Caterpillar

The cabbage cluster caterpillar lays its eggs, shaded dark cream to brown, in a large parcel on the underside of leaves. Caterpillars are somewhat translucent with dark-colored heads when they are young, turning more toward greenish yellow with white stripes as they age. Where you see one cabbage cluster caterpillar, there are likely to be more, as these pests feed in groups. Pupae are golden brown and can be located in the soil around plants. The adult moth is cream in color, with males having dark brown patterns on their wings. The cabbage cluster caterpillar tends to leave behind nothing but the skeletons of leaves along with the webbing and frass in their wake. Treat as for other cabbage worms and moths, with floating row covers, handpicking grubs and dropping into soapy water, and using Bt insecticide.

Cabbage Loopers

You can identify cabbage loopers by the motion they’re named for. These brassica pests move in a loop pattern, pulling their bodies along like inchworms. Caterpillars are light green with fine white lines that run down the caterpillar’s sides. Adult moths have brownish-gray wings with white spots in a symmetrical pattern. As with other caterpillars that feed on cabbages, treat by installing floating row covers to deter egg laying. Caterpillars can be picked off by hand and deposited into a bucket of soapy water, or treat the entire garden with nontoxic Bt.

Cabbage White Caterpillars (Cabbage White Butterflies)

Gardeners who will soon be seeing cabbage white caterpillars, also called cabbage white butterflies, may notice single eggs that are bullet-shaped in shades of yellow and orange. The caterpillars themselves are a velvety green with fine yellow striping on the sides and top. Pupae are yellowish green and usually are attached to a plant at the leaf or stem. The butterflies are white with one or two black spots, the number depending on whether the butterfly is male or female. In addition to large, ragged areas where plant matter has been eaten away, gardeners may notice the dark green droppings of the insect on plant leaves or folded into joints. Give these pests the classic treatment for cabbage worms and moths of adding floating row covers to prevent eggs being laid, picking off worms by hand and dropping into a pail of soapy water, and treating the garden with nontoxic Bt.

Cutworms

Eggs come in shades of cream to yellow with ribbing and are laid in a small cluster. Caterpillars are a grayish green, and when young, they tend to feed en masse. As caterpillars age, they turn black with markings in red, yellow, or cream. If touched or otherwise disturbed, the caterpillars tend to curl up into a protective ball. Gardeners may also see reddish brown pupae in the soil or observe the adult moths with wings patterned in gray, cream, and brown. Treat against cutworms as for other cabbage caterpillars and moths. Install floating row covers to reduce eggs being laid in the garden. Remove caterpillars by hand and drop into a bucket of soapy water, and treat the whole garden plot with nontoxic Bt.

Diamondback Moth

Pale yellow eggs appear in clumps laid on plant leaves or stems. Caterpillars are translucent at a young age, and as they grow, turn a bright yellow-green. Gardeners may find pupae woven of silvery mesh still attached to plants. Adult moths have a light brown stripe across the black of wings with a distinctive pattern of three diamonds. The diamondback moth caterpillars feed on plants from the inside, so damage may not be immediately evident. As they eat away the interior, they may make a few holes that face to the outside, which can show the damage. Treat as with other brassica pests that are moths and caterpillars. Install floating row covers to reduce the number of eggs adult moths can lay in the garden. Pick off the caterpillars themselves, dropping into a pail of soapy water, and treat the entire area with nontoxic Bt.

Mites

There are various types of mite that can plague a garden where brassicas grow. The insects and their eggs come in a variety of colors, but all mites are tiny in size. They manifest in various ways when it comes to damage, but all mites will show up in large numbers due to their tendency to colonize and ability to multiply rapidly. Treat much as you would for aphids, though with the large quantity of mites that usually show up in a garden, picking off the insects by hand isn’t recommended. You can aim for infested leaves with a pressure washer, which will be effective for all but the most delicate plants, which the high-speed spray might damage. An all-natural insecticide, either over-the-counter or a homemade mix with neem oil, garlic or onion, citrus, or a simple solution of half a teaspoon of dish soap diluted in one gallon of water can be sprayed on affected plants.

There’s no need to lose a large part of your harvest to pests, either through damage to the vegetables as they grow or through loss of plants as younger seedlings fall victim to infestation. Keep a close eye on the garden for signs of any of the insects we’ve covered (or signs that the insects are feeding), then follow the steps you’ve found here to make brassica pests a thing of the past.