How to Stop Cabbage Worms From Making Holes in Your Greens
Struggling with cabbage worms making holes in your garden greens? Cabbage worms can be one of the top destroyers of leafy greens in the vegetable garden. In this article, gardening expert Merideth Corhs walks through her favorite methods for keeping these pests away from your garden greens this season.
Cabbage worms are one of the most common pests in the home garden. In fact, every gardener I know has struggled with them over the years. They can be extremely difficult to see, create an excessive amount of damage, and populate multiple generations each season. This means that, even after you’ve eradicated one set of cabbage worms, the next generation is right around the corner!
The good news is that there are many ways you can stop cabbage worms from making holes in your brassica greens. But remember, if you’re growing an organic garden, perfection is not the goal. Instead, think of healthy pest management that minimizes crop damage as a win!
Read on to learn all about cabbage worms, the damage they cause, and how to eradicate them from our plants.
- 1 What Are Cabbage Worms?
- 2 Identifying the Damage
- 3 Seven Methods of Prevention & Management
- 4 Final Thoughts
The term “cabbage worm” is often a catchall for a handful of small green caterpillars that plague gardens everywhere. The most common cabbage worms in the United States are the imported cabbage worm (Artogeia rapae or Pieris rapae), the cabbage looper (Trichoplusia ni), and the diamondback moth (Plutella xylostella).
These pests are incredibly invasive and their quick lifecycle means they can produce multiple generations in a single season.
As the shared common name suggests, they are attracted to cabbage and other members of the brassica family. Brassicas include veggies like cabbage, broccoli, cauliflower, kale, collard greens, mustard greens, brussels sprouts, bok choy, and kohlrabi.
Cabbage moths can also attack flowers that contain mustard oil (like nasturtiums) and other members of the Brassicaceae family such as sweet alyssum. They are equal opportunity devourers!
As with all things in life, knowledge is power. It’s useful to understand the lifecycle of the cabbage worm so that you can recognize them when near your plants. If you see adult butterflies or moths near your plants, you can anticipate needing to take action against the caterpillars or pupae in short order.
For all three varieties of cabbage worm, the lifecycle is the same. The adults – butterflies or moths – feed on nectar and lay eggs on nearby plants. The eggs hatch into caterpillars or larvae that feed heavily on nearby leaves until they’re ready to pupate.
The pupae metamorphose into an adult butterfly or moth and the cycle repeats itself – many times throughout the season.
Adult imported cabbage worms are actually quite beautiful. The small 2 inch cabbage white butterfly has pearly white wings with a small black spot on each (female butterflies have two on each wing).
Adult butterflies lay their oval shaped yellow eggs on both sides of the leaves. The resulting green caterpillars are quite small (only 1” long), but can eat an incredible amount of foliage. Expect to see between 2-3 generations per season.
Adult cabbage loopers are nocturnal moths with a mottled brown appearance. Although only 1.5 inches, each female can lay up to 350 eggs on nearby leaves.
The resulting eggs are quite small but are creamy white and often clustered together. Emerging green larvae reach 1.5 inches and have thin white stripes running down each side of their bodies.
Interestingly, cabbage loopers have no middle legs so they sort of lurch along leaves and stems as they move. Annual generations range from 2-3 in colder climates like Canada and 5-7 in warmer climates like the southern states.
The diamondback moth is another nocturnal pest. The small 1 inch grayish-brown moth often has a cream-colored band that forms a diamond shape along its back. Adults lay their eggs on the underside of leaves clustered near the veins.
Emerging pupae are quite small – only ⅓ of an inch. The number of generations varies greatly from year to year but can range from 4 to 8 in colder climates, and up to 12 in warmer locations.
Damage from these garden pests is pretty obvious – you’ll notice small and large sets of holes emerging on the leaves of your brassicas.
While most damage is only cosmetic in certain plants like cabbage or broccoli, it’s a different story with kale, collards, or mustard greens. When the leaf is the crop you eventually want to harvest and eat, you don’t want cabbage worms getting there first!
Damage can be most devastating with younger plants and seedlings. In my personal experience young kale seems to be a delicacy for them, and you can lose an entire plant quickly if you don’t take action.
Seven Methods of Prevention & Management
Control and prevention often requires a multi-pronged approach. Manual removal paired with practical gardening practices is often the most effective methodology. But if you’re dealing with a major infestation, there are several OMRI approved chemical options you can use.
The best way to get rid of them is to pick them off by hand – especially if you’re only managing a small garden. If you’re at all squeamish around wrigley pests like I am, opt to wear gloves for this process!
To do this effectively, you’ll have to get up close and personal with the leaves of your plants. Make it a habit to check over your plants multiple times per week and focus on the undersides of plant leaves (or the back side of kale or other brassica greens).
They are most often found hiding on the undersides of leaves near the newest growth at the leaf center. They blend in expertly when snuggled up against the leaf stem or large veins.
Squish them by hand, and feed them to chickens, or dump them in a jar of soapy water. You can also go ahead and look for eggs while you’re removing the caterpillars. If you see clusters of white or yellow dots, just swipe them away with your finger and they’ll be gone before they can hatch and wreak havoc.
Floating row covers can be a great tool when it comes to pest prevention, especially with leafy brassicas that don’t require pollinators. Pests cannot eat and infest your plants if they cannot get to them!
You can use covers for individual plants, raised beds, or containers as long as you have the right equipment. Row covers are traditionally supported by hoop structures (pvc piping is an often used DIY material) that support insect netting.
In a container, you can use a tomato cage as the support for the netting. In either setup, the netting can be easily removed when needed for harvesting or work in the garden.
In a healthy ecosystem, the cabbage worm population can be kept low enough that the impact to your plants will be minimal. The great news is that they have a lot of natural predators including beetles, spiders, lacewings, and predatory wasps.
Birds also love the worms but can often have a hard time finding them underneath large leaves. They do a better job of catching and eating adult moths and butterflies. If you have chickens or guinea hens, they’ll also be a great resource in keeping cabbage worm populations down.
You can invite predatory insects into your garden naturally through purposeful companion planting, or purchase them for release into your garden. Just remember that if you do release predatory insects into your garden, you’ll want to have their preferred flowers and herbs around to keep them there. Otherwise, your purchased insects will fly off to more accommodating locations.
There is also some evidence that certain fragrant herbs and flowers like thyme, dill, oregano, lavender, marigolds, onions, and garlic deter cabbage moths. You can also try to use flowers like nasturtiums as a ‘trap crop’ to lure adult butterflies and moths away from your main crops.
Did you know that pests seem to be less attracted to red and purple varieties of vegetables? While this may seem largely anecdotal, many gardeners report that their purple cabbage varieties and red kale varieties exhibit significantly less damage than their green counterparts.
One reasonable assumption about this is that the small green cabbage worms simply can’t camouflage as well on a purple or red plant. This gives predators an advantage when looking for tasty cabbage worm snacks.
There is also some evidence that anthocyanin – the antioxidant flavonoid that makes red and purple veggies so good for us – is mildly toxic to caterpillars.
This tip is a little more anecdotal than some of the others, but there are gardeners who swear by it! Apparently, adult cabbage white butterflies are territorial and will stay away from plants that have other cabbage whites around. Some gardeners purchase (or create a DIY version) dummy white butterflies to place around their garden beds.
If you like this idea, definitely give it a try! But rather than making this your only strategy in fighting them, we recommend pairing it with one or two of the others.
Organic BT Spray
If you’re dealing with a really pervasive infestation this season and the other methods we’ve discussed just aren’t cutting it, you may need to turn to a harsher control method. Botanical BT is a good option in this case.
Bt (Bacillus thuringiensis) is a natural bacteria often found in the soil. When applied as a foliar spray, Bt will coat the leaves and branches of your brassicas. When they eat the leaves, the Bt paralyzes their digestive system and will cause them to die. Unlike Neem, Bt won’t bother pollinators.
Different strains of Bt work on different kinds of pests. For cabbage worms, look for Bt kurstaki. Always look for an OMRI certified product and follow package directions.
Neem is an excellent tool for any organic gardener to have close at hand. Neem acts as a natural insecticide for many pests that plague brassicas including aphids, whiteflies, hornworms, and – of course – cabbage moths.
Neem oil creates a light coating on the leaves and stems of your plants. This can stop new cabbage worm eggs from hatching and also makes the leaves less appealing to eat. If the oil is sprayed on the caterpillars themselves, it can suffocate them.
We put neem oil at the bottom of this list for a reason… You need to be cautious when spraying neem oil since it can kill beneficial insects as well as pests.
We recommend using this sparingly and only if other methods are failing you. Especially if you’ve worked hard to introduce good bugs into your space, you don’t want to create a hostile environment for them.
When it comes to trying to get rid of or prevent a pest like cabbage worms, your best bet is to use as many control methods as possible. This kind of integrated pest management approach will ensure you have the best chance of protecting your delicious brassicas this season.
While it’s unlikely that you can create a pest-free zone in your garden, you can certainly make a positive impact. Remember, the goal is balance in the garden, not sterility!