Protecting Your Cabbages From Cabbageworm And Cabbage Moth
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Cabbageworms and cabbage moths are the most common pests of cabbage. These pests can cause serious damage to both young plants as well as older ones, and extensive feeding can also prevent head formation. Therefore, early detection is essential for effective cabbageworm control.
Most Common Cabbageworm Pests
The Imported cabbageworm (the larval form of the Cabbage White butterfly having white wings with one or two black spots per wing) is velvety green with a narrow, light yellow stripe down the middle of its back. These worms tend to feed closer to the center of the plant.
Cross-Striped cabbageworms are bluish-gray with numerous black stripes running cross-wise. A black and yellow stripe also runs along the length of the body. Larvae feed on all tender parts of the plant, but prefer buds. Young leaves and buds are often riddled with holes.
Also, watch for cabbage loopers on the undersides of lower leaves, examining them for newly hatched larvae. Check around the base of the head for larger worms. They will be light green with a pale white stripe down each side and two thin white stripes down the back. In addition, the worms move in a looping motion, as they have no middle legs.
The larvae of Diamondback moths can be destructive too. Eggs are found on the undersides of lower leaves and the larvae are small, yellowish-green, with a forked tail. While they feed on all plant parts, they usually prefer the buds of young plants. Look for young larvae emerging from small holes in the underside of the leaf. Older larvae create a more skeletonized look to the leaves.
While successful control of cabbageworms depends on proper identification, timing of applications and suitable insecticide coverage, most are treated much the same. Start checking for cabbageworms in early spring or as soon as you see adult cabbageworm butterflies or cabbage moths flying around the garden.
You can also install floating row covers over crops to prevent adult moths/butterflies from laying eggs on plants. Check crops weekly for these pests and their feeding damage, examining both sides of leaves.
The best time to treat is while the larvae are still small, as older worms tend to cause the most damage. Insecticides may not be as effective in killing older cabbageworms; however, handpicking (especially in smaller gardens) is effective, dropping them into a pail of soapy water. While it is possible to use broad spectrum pesticides, such as permethrin, these insecticides will also kill natural enemies that are present in the garden.
The use of Bacillius thuringiensis (Bt), a non-toxic, biological insecticide, is effective and is specifically targeted towards worms/caterpillars. It’s also safe and can be used on most garden vegetables. Using Bt will not harm any beneficial insects, including natural enemies of these worms. Another alternative is neem oil. It’s also safe to use, effective against many pests (including caterpillars), and will not affect beneficial insects.
Additional Organic Control for Cabbage Moths
It is believed that growing cabbage with red or white clover results in fewer cabbage white butterflies and moths in part to camouflage and predators.
Cabbage moth caterpillars can also be averted by surrounding beds with strongly perfumed herbs, like lavender, or interplanting with other crops. Most moths and butterflies find food sources using scents and silhouettes; therefore, disguising cabbage plants may offer more protection.
Crushed eggshells scattered around the base of your plants may also deter the butterflies from laying their eggs.
How To Protect Your Garden From Cabbage Worms And Moths – Naturally!
Anyone who has ever grown cabbage, broccoli or cauliflower knows the damage cabbage worms and cabbage moths can do! One day your plants are healthy and vibrant, and then suddenly it looks like they have become riddled with holes like a fine block of Swiss cheese.
The Swiss-hole like damage of the cabbage worm
Before you know it, plants are wilting away, and the vegetables left on the plants look anything but appetizing.
But all is not lost! Cabbage worms and moths can can be controlled and nearly eliminated. With a little effort, there are a few simple ways to help defend your garden against these unwanted creatures.
And better yet, none of them involve spraying harmful insecticides on the very produce you hope to eat some day.
Dealing with the Cabbage Worm
The key to avoiding cabbageworm damage is to prevent the butterflies from laying eggs on plants. Once laid, the small eggs are easily overlooked. You may not know your garden has cabbageworms until you see them or their damage on your crops. While preventing damage is ideal, there is still hope for a harvest if you stop further damage promptly.
Prevention. The simplest way to prevent egg laying on your plants is to create a barrier around cruciferous vegetable plants as soon as you plant them. A tunnel-like row of simple hoops covered with protective fabric does the trick. 3 Install hoops made from PVC piping, metal or bamboo, making sure the hoops are high enough so plants will not touch them when fully grown. Seed packets or plant tags list each plant's mature height. Secure hoop ends by pushing them deep in the ground.
After planting seeds or transplanting young plants, cover the hoops with fabric, allowing at least 6 inches of fabric to sit on the ground on all sides. Commercial row cover fabrics are popular options for protecting crops, but basic tulle is more economical and readily available from local fabric stores. Place rocks, poles, bricks or other heavy objects on top of the excess fabric to keep it in place. Row covers designed in this way make it impossible for the cabbage white butterfly to access your plants.
Managing cabbageworms. Once spring arrives, watch for the white butterfly in your garden. If you decided to delay row covers, installing them at this point is still helpful. However, once sighted, it is possible she has already laid eggs. Check diligently for signs of cabbageworms or their damage. Inspect the underside of all leaves before covering crops, and remove the cover occasionally to look for eggs or damage.
If you discover crop damage, take action immediately to kill cabbageworms. Sevin ® Insect Killer, available in ready-to-use, ready-to-spray and concentrate forms, kills cabbageworms and more than 500 other insect pests by contact and keeps working to protect your crops for up to three months. For Brassica vegetables such as cabbage, broccoli, cauliflower, and kale, you can treat with liquid Sevin® garden pesticides right up to one day before your harvest.
While it may seem logical to try and eliminate the cabbageworm in its butterfly form, focusing your efforts on the destructive larvae helps keep your garden welcoming for beneficial butterflies, bees and birds. Take action early to protect your crop against egg laying and against damage from hatched cabbageworms. With the help of GardenTech® and Sevin ® garden insecticides, you can enjoy a healthy cabbage crop and the homespun treats that come with it.
Always read the product label and follow the instructions carefully, including guidelines for listed crops and pre-harvest intervals (PHI).
Sevin is a registered trademark of Tessenderlo Kerley, Inc.
GardenTech is a registered trademark of Gulfstream Home and Garden.
1. C. Klass, "Imported Cabbageworm," Cornell University, 2012
2. R. K. Walton, "Cabbage White," Mass Audubon.
3. R. Bessin and T. Coolong, "Row Covers for Insect Management," University of Kentucky Entomology, February 2010.
Identifying If You Have Cabbage Worms
All of the above pests feed on cabbages and other cabbage family crops and can be referred to as cabbage worms. They are all, however, very good at camouflaging and their eggs are very, very small and difficult to spot.
The eggs, while tiny, are typically laid on the outer leaves on the underside. The worms will likely be found in the same areas. On the underside of leaves, hiding toward the middle of the plant, etc. They are generally whitish or yellowish in color and tiny, oblong eggs. You will find them singly laid, not in groups. Groups of a similar colored, oblong egg are ladybug eggs.
Once they become a problem, you’ll find holes eaten through your plants and an infestation can easily decimate a crop to leave only the thick stems of the plant left behind.
Holes created by cabbage worms.
If you only see a hole or two, you don’t have a major problem, but if your plant has several holes in it, you already have a major issue with caterpillars or cabbage worms.
The easiest way to identify and combat a problem in the early stages is you’ll see frass, or fecal matter, on your plant. It looks like small, yellow, brown or greenish spots all over the place, usually in groups. If you routinely check your crops, you’re going to see the frass before you find any other signs of cabbage worms.
Cabbage worm frass (or fecal matter).
Cabbage worms can be devastating to an otherwise-healthy garden. Here are a few things you might not know about these garden pests, as well as several ways to keep your plants safe from them. Remember: knowledge is power!
Bad News Butterflies
Everyone loves butterflies, but there is one butterfly that I bet you don’t love, especially if you are trying to grow broccoli, kale, cabbage, or any other cole crop: the White Cabbage Butterfly (Pieris rapae), also known as the Imported White Cabbage Moth.
Since they can overwinter in garden debris, White Cabbage Butterflies are one of the first butterflies to emerge in the spring. Even before the broccoli was planted, I saw them flitting around the garden just looking for a likely place to lay some eggs.
Identifying White Cabbage Butterflies
The butterflies are small (1½–2 inches across) and yellowy-white with black markings. The female has two black spots on her forewing while the male has only one spot. The adult butterfly isn’t the problem, it is the larvae that do all the damage.
The Dreaded Cabbage Worm
If you have seen velvety green worms on your kale or cabbage plants, you have cabbage worms. They blend in well with their green surroundings making them hard to spot until you start to notice large hunks of leaf are disappearing. They also poop as they eat leaving behind large amounts of dark brownish-green excrement called frass. Sometimes that is your first hint that something is wrong. Later on, they will burrow inside your cauliflower or deep into your cabbages, spoiling the head.
Like many of our garden pests, cabbage worms were accidentally introduced from Europe into Quebec in the 1860s and rapidly spread to most of North America. The imported cabbage moth/white cabbage butterfly has a 3 to 6 week lifecycle. Adult females lay white, rocket-shaped eggs singly on the underside of a brassica leaf. The eggs turn yellow as they mature, hatching after 7 days.
One busy female can lay 300 to 400 eggs in her 3 week lifetime and she will fly several miles looking for the right host plants. The larvae are hungry when they hatch out and eat constantly for 2 to 3 weeks before they pupate, turning into a butterfly about a week later. Then the cycle begins again. Is it any wonder that the kale looks like Swiss cheese and the broccoli is worm-infested?
Cabbage Worm’s Natural Predators
Luckily, cabbage worms do have a few natural enemies, including yellow jackets, paper wasps, and birds. Many songbirds gobble up not only the worms but the butterflies as well. Chickens, ducks, and guinea fowl find the worms to be quite tasty, so once your plants are big enough to withstand some pecking and rough treatment from the birds, turn them loose in the garden.
Parasitic wasps lay their eggs on the worms and when those eggs hatch out, the larvae will eat the worms from the inside out, so leave any worms you see with white cocoons on their backs alone. They will eventually die a horrible death and the parasitic wasps will live to kill off more bad guys in your garden. It is a worm-eat-worm world out there!
How to Get Rid of Cabbage Worms
- You can resort to using diatomaceous earth, which cuts up any soft-bodied insect that comes in contact with it. Or you could try Bt (Bacillus thuringiensis var. kurstaki) a natural bacterium that kills caterpillars and worms. Both will need to be reapplied after rain.
- There are other natural controls, like handpicking the nasty worms off the leaves, which is tedious and you always miss some, especially in the broccoli. They hide among the florets and you usually don’t notice them until you have cooked up a batch for company and someone finds a bloated white worm on their plate. Yum!
- Red-leaved cole crops are less attractive to the cabbage butterfly as a spot to lay her eggs, since they will not camouflage the baby worms well. She is a discerning mother I guess.
- Some people grow a trap crop of nasturtiums or mustard—plants the butterfly prefers—and when those plants are covered with worms they dispose of them. Companion planting with aromatic herbs such as thyme, sage, rosemary or oregano is said to repel the butterflies too.
- Covering plants with floating row cover works well. We bought extra wide reemay (a thin, cloth-like material) to cover our cole crops with since the broccoli gets so tall but in a really hot summer it can heat up too much under the cover.
We switched to using screen cloth to cover the plants and that has worked very well for us. It keeps the moths at bay and the brassicas worm-free!
- One clever idea I have seen is to make moth-shaped decoys out of plastic or paper and place them in the garden. Supposedly the butterflies are territorial and will not deposit their eggs if they think another female has staked her claim to that area. Make the decoys 2 inches across and be sure to mark them with 2 black spots on the upper wing. Here is a link to a page of printable decoys: Cabbage Butterfly Decoy. If you try this method, let me know how it works!
For more tips on dealing with cabbage worms, check out our Cabbage Worms Pest Page.
To control cabbage worms without chemicals, put row covers over your plants early in the spring, before the cabbage butterflies have taken wing. The covers prevent the adults from reaching your plants to lay eggs on them, which prevents any cabbage worms from hatching out onto your plants. If you spot cabbage worms or other pests, pick them off by hand and drop them into a bucket of soapy water to drown. Remove weeds that provide hiding places and remove the plants or till under your entire garden at the end of the season to break the worm’s life cycle.