How to Identify and Control Cabbage Worms

Cabbage worms can rapidly destroy a brassica plant and feed on all types. Kevin Espiritu discusses control and prevention methods to keep them at bay.

Cabbage worms in vegetable garden.

Contents

Growing cabbage can be such a rewarding experience. But it’s terrible to harvest cabbage after winter has passed and find out it’s been a snack for cabbage worms. It’s important to monitor your cabbage, identify pests, and control cabbage worms as quickly as possible. Unchecked, they can do a lot of damage to your whole crop. 

Among the cabbage industry, they’re known as imported cabbage worms because they were first discovered in Canada and disappeared for a while to emerge in the Southern US, especially in the Gulf Coast. Today, temperate regions across the world host it and its adult form, the cabbage white. 

Another reason to be vigilant is that they don’t just go for cabbage plants. They eat Brussels sprouts, mustard greens, and radish too, among others. Knowing what to do is your first line of defense in dealing with these maligned worms. 

What Are Cabbage Worms?

Plastic bucket filled with black and yellow caterpillars picked from the garden.
The cabbage worm is primarily a pest of cabbage.

The cabbage worm is the larval form of the small white or large white butterfly, both commonly known as the cabbage white butterfly. They are common in temperate areas of the world and were first discovered in North America in 1860. 

It spread rapidly to other areas of the continent, and by 1886 was well established in states in the Gulf Coast and the Rocky Mountains. The cabbage worm is primarily a pest of cabbage, but also attacks other brassica crops – or those in the mustard family – and vegetables. 

Where there is a brassica, there is often imported cabbage worm and their cousin, the cabbage looper. They live out several life cycles in a year. In areas where temperate weather lasts year-round, they’re particularly damaging. 

Similar Pests

Green cabbage looper on plant stem.
Cabbage loopers are often confused for cabbage worms.

There are other moths or butterfly insects from the Lepidoptera order often included in the cabbage worm category. These include the cabbage looper (Trichoplusia ni), the cabbage moth (Mamestra brassicae), the cabbage webworm (Hellula undalis), the orange tip butterfly (Anthocharis cardamines), and the diamondback moth (Plutella xylostella or Plutella maculipennis). 

Their life cycles and reproduction may be different from the Pieris genus, but they attack similar plants and are often eliminated in similar ways.

Cabbage loopers are often confused for cabbage worms. It’s important to know the difference between them because their treatments are different. Be sure you’re not dealing with the cabbage looper before you spring for biological controls or pesticides.

Types of Cabbage Worm

There are two species we’ll focus on in this piece. Both of these develop into different types of cabbage white butterfly, so these worms are a green caterpillar in either larval form. 

Pieris rapae

White Pieris butterfly on yellow flower in the garden.
The term ‘small white’ comes from the coloration of the adult butterfly.

Small white butterflies (Pieris rapae) are widespread across Europe, Asia, North Africa, and South America. It also has been accidentally introduced to North America, Australia, and New Zealand.

Its larva, imported cabbageworm, is a major pest in commercial agriculture due to its feeding habits. The term ‘small white’ comes from the coloration of the adult butterfly, which is white with a few black markings on its wings. Pieris rapae is smaller than its related brassicae relatives.

Pieris brassicae

Pieris brassicae larvae feeding on green vegetable leaf.
The Pieris brassicae worms are incredibly damaging to crops.

The large white (Pieris brassicae) is common throughout Africa, Asia, and Europe, and has been accidentally introduced to Australia and New Zealand. While it’s fairly uncommon in North and South America, it is not completely unknown there and has been reported in the northeastern United States on occasion.

As an adult, it is a large white butterfly with black dots on its wings and large black patches at the wingtips.

Life Cycle

Pupa of cabbage worm caterpillar.
An adult cabbage butterfly emerges from a pupa.

Cabbage whites lay their eggs on the underside of plants in the Brassicaceae family. These host plants are good food sources for larvae. Small whites tend to lay a single egg on a given leaf, whereas large whites tend to lay eggs in large numbers on a singular leaf.

When the small white eggs hatch, tiny velvety green larvae with dark heads emerge. At this point the legs are not heavily defined, thus they are regularly referred to as worms or the term ‘cabbage worm’. 

As the larvae feed, these tiny worms go through five larval phases or instars during which coloration changes, becoming larger and more uniformly light green with fewer dark patches as it molts between each phase. When imported cabbageworms are fully-grown caterpillars they form a pupa, from which will eventually emerge an adult cabbage butterfly.

The life cycle of the large white is nearly identical except for the coloration of the caterpillar. Large white caterpillars tend to be yellowish in coloration with a brown head. As they go through their larval phases, brown spots along the sides manifest. It similarly pupates, and eventually an adult large white will emerge.

What Do Cabbage Worms Eat?

Cabbage head with holes in the leaves from cabbage worm feeding.
Brassicas are favorites of these pests.

This little green worm likes to live where it eats. But because it’s found around the world, it has a surprisingly wide diet. You’ll find eggs laid on the underside of leaves of cabbage crops and other plants in the cabbage family. When they hatch into worms, they eat their way around and through your brassica plants. 

While you can find them in ornamental gardens as well as those containing other cabbage family crops, usually the first sign to watch for is white butterflies. Most likely these are cabbage white butterflies. Where they are, there are likely to be green cabbage worms.

They prefer plants that produce natural glucosinolates or glucosides. This includes nearly every cruciferous food plant. They’re fond enough of broccoli that they’re occasionally called broccoli worms.

While other crops are susceptible, they do prefer to stick with ones that provide those natural glucosinolates. However, they have been reported to impact tomato plants, spinach, lettuce, and other garden crops.

Identifying Cabbage Worms

White butterfly pollinating yellow flower in the garden.
Look out for cabbage butterflies to identify a problem.

Identify cabbage worms and cabbage worm damage by their presence on your plants or by the presence of cabbage butterflies fluttering around the base of plants.

You can tell they’ve been there by the byproducts left as the pests feed. Their dark greenish-brown and spherical fecal matter is left behind in the areas where they feed. In this case, there are likely to be holes in cabbage leaves or heads, or in whatever crop you’re growing. 

You might think this is no biggie since cabbage heads develop in layers of thick leaves. But worms can bore into heads by chewing a series of irregular holes in leaves. 

Another indication you have a cabbage worm problem is the presence of eggs. These are usually whitish or yellowish and elongated, with a point at the top and pointed ridges down the sides. 

Control

Now that we’ve covered identifying cabbage worms and their damage, let’s talk about prevention and treatment.

Note that if you check your plants and find cabbage worms on more than 10% of your crop, it’s best to treat every plant of that type to prevent future issues. If you’re growing just a few plants they like, treat them all from the get-go.

Cultural Control

Hands picking cabbage worms off of cabbage plants.
If you see any worms, pick them off your plants.

The best form of controlling this garden pest culturally is to keep the area where you’re growing your Brussels sprouts, cabbage, or turnip greens free of weeds that host them. Any weeds in the brassica family are key targets for the cabbage white butterfly. 

Another viable control involves crushing eggs. If you see them, either singly or in clusters, put on a pair of gloves and carefully remove them from the leaves of your plants. Rinse them off in soapy water and dispose of them, or crush them. Similarly, if you see the caterpillars themselves, pick those off and destroy them.

Companion planting is another great cultural method of controlling these pests. Companion plants that deter cabbage worms include borage, thyme, chamomile, and celery. The worms detest the taste and smell of celery. Companion planting with borage and chamomile keeps moths and butterflies away. The scent of thyme overpowers the scent of host plants worms love to munch on. Trap crops like mustard are great companion plants as well.

Remove plant debris that may have eggs or worms on it. Remove a few leaves on your plants if they have eggs on them. Do not compost them. Instead, destroy them to prevent further issues. 

Biological Removal

Bird feeder hanging from tree in garden.
Encourage birds into your garden to feed on the worms.

The most popular organic pest control – and one of the most effective – is the use of Bacillus thuringiensis var. kurstaki. Commercially, this is generally referred to as Bt or BtK.

Spraying this bacteria on your plants won’t harm the plants, but it will harm caterpillars and worms who feed on the plants. However, it can potentially harm some beneficial butterfly larvae (like monarch caterpillars), so don’t use this unless you can see the worms or their yellow eggs. 

Some people use food-grade diatomaceous earth powder on the leaves of their plants. This material, which doesn’t harm humans at all, will cut the worms’ soft bodies and cause them to dehydrate and die. It can also harm other insects as well, though. 

Cabbage worm’s natural enemies include yellow jackets, parasitic flies, parasitic wasps (such as Trichogramma wasps), green lacewing, predatory beetles, spiders, and birds such as the house sparrow or skylark.

Sometimes you can find colonies of their natural predators in nurseries. Buying these and unleashing them on your crops is only one part of the process. You’ll need a well-established habitat for them to dwell in. Plant yarrow, parsley, Queen Anne’s lace, coreopsis, and others to encourage the natural habitation of beneficial insects, like parasitic wasps in your garden. 

Insecticidal Removal

Person using an orange spray bottle to spray cabbage plants and protect from cabbage worms.
Neem oil can help control, but not remove, cabbage worms.

Outside of BtK, there aren’t many organic insecticides that treat cabbage worms while they are feeding. Neem oil is useful, but only to coat and suffocate the eggs cabbage butterflies lay.

If you’re going to spray neem on flowering plants, do so in the morning before the sun rises and peak pollinator activity ensues. An alternative to this time is at dusk before nocturnal pollinators come out. 

Several chemical pesticides have shown effectiveness on brassicas. However, these are the riskiest forms of treatment and tend to remain in plant tissues for some time. Avoid this if possible.

Prevention

Picked cabbage worms in plastic bag.
Stop butterflies from laying eggs on your plants to interrupt the cycle.

One of the simplest techniques used to prevent cabbage worms is to use floating row covers of fine nylon mesh over your plants. If you can keep the butterflies from reaching your plants in the first place, you keep the butterflies from laying eggs. Row covers also provide a little shade for your plants.

Another option is to use garlic sprays that repel cabbage moths and butterflies, keeping them from laying eggs on your plants. You can buy garlic oil sprays, but you can also make your own

Caterpillars also don’t like citrus, so you can make a citrus repellent. Grind up the rinds and seeds of any type of citrus fruit. Soak the ground citrus parts in two cups of water overnight, then strain out the pulp. Add two teaspoons of dish soap to this and mix thoroughly. Spray all of the plant’s surfaces with that.

Neem oil may also be good on its own. While it doesn’t prevent the butterfly from laying its eggs, neem oil can make it less likely that the eggs will hatch if they’re drenched with it. It also coats the surface of the leaf and leaves a bitter flavor, stalling the worms from eating your plants.

Sticky traps posted up next to your plants, or even next to floating row covers as a second line of defense will trap cabbage moths – like the diamondback moth, for instance – preventing egg-laying as well.

Finally, green cabbages are more likely to suffer attacks by cabbage worms. Reduce the occurrence of cabbage worms by planting red and purple varieties. With so many kinds of purple cabbage, you have lots of options!

Frequently Asked Questions

Can you eat cabbage with worms?

That’s not advisable, due to the likelihood of parasitic worms present in their bodies.

Will baking soda kill cabbage worms?

While this is a widely used and touted method, it will not harm the worms.

Will vinegar get rid of cabbage worms?

This is another widely accepted mode of killing them, but doesn’t work. Instead, use the methods listed above.

Do cabbage worms attack any ornamental plants?

Yes! Not all of the Brassicaceae family of plants are edible to humans, and they can be ornamentals. One of the most likely ornamentals to be attacked is alyssum, but nearly any of this plant family is subject to infestation, as almost all of the plant family has natural glucosinolates. If you’ve got alyssum, lunaria, or other ornamentals that fall into this family of plants, they could be targeted.

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