If you see green, small worms on the underside of the brassica plants like kale, you’ve got a cabbage worm problem, and this is the cabbage butterfly larvae. There are several cabbage worm species available, and the most common ones found throughout the United States are the cabbage looper, imported cabbage worm, and the diamondback moth.
The cabbage worm larvae feed extensively on cruciferous vegetable crops like Brussels sprouts, broccoli, cabbage, collards, cauliflower, kale, horseradish, mustard greens, kohlrabi, rutabagas, radishes, turnip greens, adn turnips. They can also go after flowers that have mustard oil in them, like nasturtiums or members of the Brassicaceae family like sweet alyssum. The adult butterflies or moths sip nectar from flowers and don’t cause the damage the larvae do. However, there are ways to get rid of them, and we’ll outline 11 of them below.
Cabbage worms can be huge pests once they take hold, so you want to do everything you can to prevent them and save your crops.
What Cabbage Worms Look Like
It’s good to know what the adults and larvae of the cabbage worm look like, and you also want to know their life cycle because seeing them by your plants most likely means that you can expect to see damage soon.
While the number of generations and lifespan of the cabbage worm varies, the three species all have similar life cycles. The adults, both moths and butterflies, feed on the nectar and lay eggs in the host plants. The eggs hatch into larvae or caterpillars that feed on the host plants, and they then go to a protected area on the plant to pupate. They metamorphosize into adults and start the cycle over. The most common cabbage worm types include:
The adult cabbage loopers are nocturnal moths, so you won’t see them out and about during the day. They have brownish-gray mottled wings with a 1.5-inch span. They tend to lay the eggs on the undersides of the leaves of the host plants, close to the ground. Their eggs are creamy white and roughly the size of a pin head. The larvae are a pale green color with thin white stripes that run down each side of the body. The mature larvae are roughly 1.5-inches long, and they have no legs on the middle section. They feed on the plants for two to four weeks. When they move, they do an odd looping motion as they have no legs in their middle section, and this is where the name comes from. In hot climates, they have five to seven generations a year, and cold climates have two or three generations.
This nocturnal moth is a light brown color with a more slender wingspan of roughly an inch. They get the name from the whtie diamond pattern you can see when they fold their wings. They lay their cream-colored, tiny eggs near leaf veins. The mature larvae are only a third of an inch long, and this is much smaller than the larvae of the cabbage loopers and imported cabbage worm. The larvae are tapered and light green, and when you disturb them, they wiggle back and forth so rapidly that they drop off the plants. How many days they feed on your plants depends on the temperature and how available the food is. The number of generations per year has a wide range, from 4 to 12, with warmer regions seeing more generations.
Imported Cabbage Worm
The adult butterflies are ones that you can see flying around in the daylight. They’re an off-white color with one or two blackish-gray spots on each forewing. They have a two-inch wingspan, and the adults lay the eggs on the underside and upper sides of the leaves. The eggs have an oval shape with a yellow coloring, and the velvety green larvae get up to an inch long when they mature. They have yellow striping running down their sides and back, and they feed on the host plants for up to 15 days. They move very slowly when you disturb them, and they produce between two and three generations each year.
Cabbage Worm Life Cycle
Cabbage worms will lay the eggs on the underside of the leaves of plants in the Brassicaceae family. These host plants are great food sources for the larvae. Small worms tend to lay a single egg near any given leaf, while larger species tend to lay a bigger amount of eggs on a single leaf. When the eggs hatch, they give way to green larvae with dark heads. At this point, the legs won’t be heavily defined. So, they’re usually referred to as worms, or cabbage worms.
As the larvae start to feed, these tiny worms go through five larval phases where the coloration changes, and they get more uniformly light green with a few dark patches and grow larger. They molt between each of the five phases, and when imported cabbage worms reach maturity, they form a pupa that the adult cabbage worm butterfly will emerge from.
The life cycle of the other types of cabbage worms is nearly identical except for the caterpillar’s coloration. Large white caterpillars tend to turn a yellow color with a brown head. As they go through the larval phases, brown spots along the sides appear. It pupates to form a large moth.
Even though cabbages have thicker leaves, cabbage worms can bore through them to create very large holes as they mature and move through the life cycle.
Popular Cabbage Worm Hosts
This little green cabbage worm loves to live on the food source. But, because you can find it around the globe, it has a wide diet. You will find the eggs on the undersides of the leaves of cabbage crops and other plants in the cabbage family. When they hatch in worm form, they can easily eat through your brassica crops. You can also find them throughout your ornamental garden as well as any garden that has cabbage family crops in it, and whtie butterflies are the first sign to watch for. These are most likely cabbage white butterflies, and you’re likely to find green cabbage worms behind them.
Cabbage worms prefer plants that produce natural glycosides or glucosinolates. This includes virtually every cruciferous food plant. They like broccoli so much that it’s common to hear them called broccoli worms.
A few more plants that cabbage worms love to eat and you should keep and eye on include arugula, bok choy, bomdong, broccoli, broccoli rabe, broccoli romanesco, Brussels sprouts, cabbage, cauliflower, choy sum, cime di rapa, collard greens, daikon, gai lan , garden cress, horseradish, kale, kohlrabi, komatsuna, mizuna, mustard greens, Napa cabbage, radish, rutabaga., savoy cabbage, tatsoi, turnips, wasabi, and watercress.
Other crops are also susceptible, but cabbage worms usually prefer to stick to the ones that give them natural glucosinolates. However, they can attack your tomato plants, lettuce, and spinach crops. However, commonly, these plants are under attack by misidentified cabbage loopers.
Identifying Cabbage Worm Damage
You can identify cabbage worm damage and the pests themselves by seeing them on your plants or by seeing the cabbage butterflies fluttering about. You can tell that they’ve already been in your crops by the byproducts they leave. They leave dark brown, spherical fecal matter in any area where they feed. Also, there are likely to be holes in the cabbage heads or leaves, or in whatever crop they’re attacking.
You may think that this isn’t a big deal since cabbage heads form thick layers of leaves, but the worms can bore right into the cabbage heads by chewing several irregular holes in the leaves. Another clue that you have an issue with cabbage worms is spotting the eggs. They are usually an off-white or yellow color with an oval shape, and they have ridges down the side with a point on top.
Controlling Cabbage Worms – 11 Options
Now that you know how to spot cabbage worms and the damage they can cause, it’s important that you learn how to prevent and get rid of them. If you check your plants and find cabbage worms on more than 10% of the crop, it’s best to treat every plant to help control it.
1. BT Spray
BT (Bacillus Thuringiensis) spray is a very fast way to help get rid of cabbage worms. As a positive, it’s non-toxic to bees and mammals. You should follow the instructions on the container for how you use it properly. You can also put some into a syringe and stick it directly into any spots that show that the cabbage looper was present.
- HappyDIYHome Warning: BT can and will kill monarch caterpillars, so take care when you spray it. If you have the space, you can create a safe area that supports monarchs well away from the sprayed area.
2. Companion Plants
It’s possible to deter the cabbage worm from every taking hold in your garden by choosing the right companion plants to put near your cruciferous vegetables. You want something with a strong scent to help confuse the Cabbage White Butterfly to stop them from finding your cabbage and other brassica crops.
Planting a section or row of beneficial plants throughout your garden beds to act as nurseries for beneficial insects is also a good idea. Beneficial insects include praying mantis, parasitic wasps, and green lacewing. A few popular companion plants to consider include:
Plant these crops around your cabbages to help keep the cabbage worms away from the start. An ounce of prevention is worth it.
Companion plants are a great way to help prevent cabbage worms from wreaking havoc on your garden, and there are many plants to choose from.
3. Ducks to Eat the Worms
Ducks, songbirds, and chickens will all eat cabbage worms and butterflies if they have the chance. So, invite them into the garde. However, chickens can try to eat the cabbage itself, so we recommend switching to ducks. They enjoy eating cabbage worms and will go after them if they get the chance.
4. Homemade Cabbage Worm Spray
You can easily make a spray to use out in your garden to coat the plants to make them inedible to your cabbage worms. To do so, you will:
- 1/4 cup vinegar
- 3/4 cups water
- 1 teaspoon of soap
Once you mix everything in a bottle, give it a little shake. To use this spray, keep in mind that you’re not trying to saturate the leaves and the plants can’t be small seedlings. We also recommend testing it on a small area of your plant to see how it reacts before you go at the whole thing. Spray your plants in the evenings out of the scorching sun, and the soap will help the mixture stick to the leaves. Spray it sparingly on the top and bottom of each leaf on the plants. Also, be aware that it does have vinegar in it, and vinegar can be a natural herbicide. However, as you’re diluting it, you shouldn’t have problems with your mature plants.
5. Insecticidal Soap Spray
Insecticidal soap will kill the caterpillars on contact, so this is a good idea if you’re not crazy about the thought of picking them off by hand. It will only work if you spray it directly on the cabbage worm, and it has zero residual effect. You can purchase pre-made organic insecticidal soap or make your own. You can mix a liter of water with a tablespoon of mild liquid soap and spray the leaves as soon as you start seeing damage. The soap works on the eggs and small caterpillars. Make sure to spray the leaves too.
6. Invite Beneficial Insects to Your Garden
Garden pests all have natural predators, and there are many of them. So, invite all of the cabbage worm’s natural enemies to your home. Yellow jackets, Trichogramma wasps, lady beetles, green lacewings, and spiders all eat cabbage worms. The most popular beneficial insect to invite is Trichogramma (parasitic) wasps. You can actually buy these wasps and release them. Unlike the annoying, large stinging wasps you’re most likely picturing when you hear the word wasp, these are harmless to humans and very small. You’ll find their eggs on caterpillar’s backs, especially tomato hornworms. However, parasitic wasps will kill all of the caterpillars in your garden, so if you raise butterflies like monarchs, don’t get them.
7. Manual Removal of Cabbage Worms
Are you someone who is comfortable handling insects? If so, manually removing and squishing certain pests right when you see them is one of the quickest, easiest, and most effective ways to manage garden pests, especially if you only have a few plants in a container garden. This includes hand-picking the cabbage worms and caterpillars from your cabbage or leafy greens or squishing aphid colonies.
To reduce the damage cabbage worms can cause by hand, you’ll need to frequently inspect the plants. Make it a habit to check all of the plants once or twice a week. Keep in mind that cabbage worms like to hang out on the underside of the leaves or tucked into new growth near the center of the plant. Some cabbage worms also like to lay along the center vein of kale leaves, and this blends them in very well. Along with the holey leaves, look for waste products as cabbage worms tend to produce a lot of it as they feed.
It can be very effective to collect or squish cabbage worms by hand, and you can also go after cabbage moth eggs at the same time. Look at the underside of the leaves for the oblong, little yellow or whtie dots and wipe them away. This removes them before they can do any damage.
8. Neem Oil
Neem oil is a plant-based oil that gets extracted from the seeds of the neem tree from India. Concentrated neem oil gets diluted and mixed before getting sprayed onto plants as an organic form of pest control. Neem oil is especially effective for controlling a host of soft-bodied insects like thrips, aphids, mealybugs, spider mites, white flies, and scale. When you apply it directly, neem oil can coat their bodies and kill them by interfering with their feeding and reproduction.
Neem oil is also great for repelling mosquitoes, cabbage moths, and flies. So, routinely spraying the whole garden with the neem oil solution can make your plants much less attractive to pets. However, if you already have a cabbage worm infestation, neem oil won’t kill them. IF you want to use neem oil in the garden, you have to know how to mix and use it properly to avoid damaging your plants. Since it doesn’t harm beneficial insects and it combats fungal diseases, it works well in organic gardens. However, if you apply it incorrectly, it can do a lot of harm.
Neem oil is a very popular organic pest control and removal tool you can use by making a spray and treating any infected crops you have.
9. Plant Purple & Red Varieties
Did you know that a lot of pests are less attracted to purple and red vegetables? Year after year, purple cabbage and red kale have far less damage by aphids or cabbage worms than the green counterparts. One theory is that the green or pale pests can’t blend into these colors well or hide easily, and they can on green-colored vegetables. This makes them a very easy target for predators. Also, the antioxidant-rich flavonoid (anthocyanin) that makes purple, red, or blue-pigmented vegetables so healthy is mildly toxic to caterpillars, and it can deter larger rodents too.
So, picking out purple or red cabbage varieties is one way to help avoid or reduce the damage cabbage worms can do. However, if you’re after more variety in your garden and don’t want to stick to these colors, the following tip can help.
10. Row Covers
One of the best ways to prevent cabbage worms from feasting on your plants is to prevent them from taking hold in the first place. Raised beds, individual plants, or sections can get protected by installing row covers that were traditionally supported using wooden hoops. Also known as “floating row covers,” they block out undesirable elements and pests. Some row covers come specifically designed to stop insects, and others can work to provide shade or frost protection.
You can easily get a combination of sleek hoop row covers with insect netting, and there are shorter ones that work in two or three foot wide beds. They come with base extenders that allow them to fit across four and five foot beds too. To give your plants more head room or arch for tomatoes and Brussels sprouts, you can get hi-rise loops. It’s possible to make some from PVC pipe too if you’re a handy person. You can pull back the row cover material whenever you need without an issue and leave the hoops in place.
If you use the right material and tuck the corners tightly into the sides, they will work well to keep the cabbage worms out, along with their caterpillars and other pest insects. They also protect your crops from rabbits, squirrels, cats, birds, and larger pests too. However, they also block out pollinators. However, this isn’t an issue as the cabbage plant family doesn’t require pollinators to grow.
11. Tansy Oil Spray
The final option on the list is tansy oil, and it works very closely to how neem oil does. It’s a natural, organic, great way to keep cabbage worms from taking hold. You can spray above the crops using this oil to deter them from laying eggs in the area. It’s not a 100% foolproof method, but it’s good for helping break up the reproductive cycle.
Cabbage worms can be a real problem with your crops, but you now know how to spot them, various types, and 11 ways to get rid of them, including DIY recipes. You can take this article and use everything you learned to protect your crops and secure a large harvest this fall.
Jen is a master gardener, interior designer and home improvement expert. She has completed many home improvement, decor and remodeling projects with her family over the past 10 years on their 4,500 sf Victorian house. She is also a passionate farmer who keeps goats, chickens, turkeys cows and pigs on her farm, and an instructor for her community’s Organic and Sustainable Farming project.