Ugh, It's Cabbage Looper Caterpillars!

I’d been gardening for a couple years when I came up with a business plan to sell homegrown salad greens to my neighbors. My husband helped me double our raised-bed garden square footage in the backyard, and I filled every single one of those beds with lettuce seeds. 

I was ready to harvest and do my first test run of washing, sorting, and packaging the leaves when I encountered a problem. 

Cabbage loopers. 

The leaves I brought inside to wash in my kitchen sink were infested with wriggling little green caterpillars that were chewing away at my business idea—fast!

Ugh!

Cabbage loopers (Trichoplusia ni) are pretty destructive garden pests that can be found in gardens like mine all across North America during the warmer months of the year. 

It’s when they look like innocent little green caterpillars that these guys can inflict the most damage. Larval cabbage loopers eat three times their body weight in plant material every single day! 

If I was finding these pests at this stage, that only meant there were likely hundreds more destroying my product. 

This is how I learned the hard way that an ounce of prevention may be worth a pound of cure, but it’s actually yards that are going to save your garden from cabbage loopers. (I’ll tell you how in a bit.)

Cabbage Looper Damage

Large holes on your leaves are usually the first sign that your garden has cabbage loopers. A good indication that it’s cabbage loopers and not some other pest is when the damage is concentrated on Brassicas like cabbage, broccoli, cauliflower, and kale. (Though as I learned the hard way, they also have been known to enjoy a lettuce leaf or two hundred.)

Younger cabbage loopers eat from the bottom of leaves, while older ones will create large, ragged holes in the leaves. They can inflict much more damage to your cabbage plants that most other pests because they won't just eat the older leaves wrapped around the developing cabbage head; they'll bore right through the entire head.

Another indication that you have a pest problem is their slimy poop. Yup. It’s gross, I know. Birds gotta fly, fish gotta swim, pests gotta get rid of all your yummy plant parts they've consumed.

You also might find cabbage looper eggs affixed to the leaves of your plants. They're round and pale green to yellowish white in color.

The bad news is, once they’ve discovered that your garden is one big tasty buffet, cabbage loopers can be difficult to get rid of. 

What Do Cabbage Loopers Eat?

The traditional vegetable "hosts" for these pests are cole crops—broccoli, cauliflower, Brussels sprouts, and of course, cabbage. These plants all come from the brassica family and make particularly enticing snacks for lots of hungry pests. 

Cabbage loopers don’t stop there though. A leaf is a leaf, and these guys need lots of leaves to grow. They’ll even go after the leaves of some of your flowering plants.  

Cabbage loopers will eat: 

• Alfalfa
• Arugula
• Beets
• Broccoli
• Brussels sprouts
• Cabbage
• Cantaloupe
• Cauliflower
• Celery
• Chrysanthemums
• Collards
• Cucumbers
• Hollyhock
• Kale
• Lettuce
• Lima beans
• Mustard greens
• Parsnips
• Peas
• Potatoes
• Radishes
• Rutabaga
• Snapdragons
• Spinach
• Squash
• Sweetpea
• Sweet potatoes
• Tomatoes
• Turnips
• Watermelons

On a commercial level, cabbage loopers threaten cotton and tobacco crops.

How They Roll — The Cabbage Looper Life Cycle

Cabbage loopers begin their super annoying presence in this world when they hatch from pale green eggs deposited by their super annoying moth parents on the top or bottom of leaves. Baby cabbage loopers start off white, and as they consume their first leaves, they begin to turn that characteristic light green. 

Cabbage loopers are most recognized in their larva stage, when they’re pale green caterpillars with white stripes down each side of their body. They’re also named for this stage, thanks to the way they loop their bodies to move. They’ll spend 2 to 4 weeks wreaking havoc on crops and doubling their body size, until it’s time for them to build their unimpressive little cocoons on the undersides of leaves. After that, they’ll emerge as gray-brown moths within just 10 days. 

A female cabbage looper moth may only live 10 to 12 days, but she's capable of laying 300 to 600 cabbage looper eggs during that short period. 

These eggs hatch in 3 to 4 days, and the whole super annoying cycle starts anew. 

With time frames like these, you can easily see how cabbage loopers can produce several generations per year in warmer climates. This is why preventing adult moths from ever entering your garden is so important. 

The Best Form of Cabbage Looper Control Is Prevention

Take it from me and my caterpillar-infested garden. Put most of your tending efforts toward protecting your greens from pests and disease rather than treating problems once they arise.

Honestly, having an ideal setup of raised beds filled with nutrient-dense soil goes a long way, as do tending practices like following good watering habits and feeding your plants regularly. Gardens that are too dry or too wet or that are filled with nutrient-deprived, struggling plants are an invitation to pests and disease, whereas well-tended plants can often fend off disease and pest threats on their own.

Two particularly important aspects of your garden setup when it comes to cabbage looper prevention are (one) making the space as inviting as possible to natural predators and (two) using garden covers.

Let's look at each of these.

Inviting Natural Cabbage Looper Caterpillar Predators

Cabbage looper larvae have many natural predators, including birds and beneficial insects. Roll out the welcome mat for these "garden good guys", and they'll help take care of any problems for you.

Add a bird bath or fountain to your backyard. Plant herbs like cilantro, dill, and parsley. Plant flowers like sweet alyssum. Doing simple things like this can invite creatures that prey on caterpillars.

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Using Garden Covers to Keep Cabbage Looper Moths Out

A few yards of tulle or garden mesh can be the simplest and most-effective form of organic pest control there is.

All you have to do is install some hoops across your garden beds and then drape cloth such as tulle, agricultural mesh fabric, or floating row covers over them to create a tent over your plants. The tiny holes in these covers allow sunlight, water, and air to flow through to the plants, but they're small enough to keep out moths, slugs, beetles, leafhoppers, and caterpillars. If moths never have access to your garden, they can't very well land on your leaves and lay their eggs, can they?

This simple barrier can prevent all kinds of critters from entering your bed, saving all the beautiful greens for you to enjoy—not the pests!

You do, however, have to time it right.

As soon as you plant your seeds or starter plants, it’s important to cover. Waiting a few days or weeks, especially after the first leaves appear, can mean you’ll end up trapping the pests inside the garden instead of keeping them out. 

Once your greens are protected with a cover, you’ll just lift the mesh when you need to tend or harvest your plants and then secure the cover with landscaping pins until next time. Protection for leafy greens is easy, but you will need to remove this type of physical barrier for fruiting plants once they need pollination from bees and butterflies. Those covers don’t just keep the bad bugs out; they bar the good ones too. 

If you're just growing greens, then covering is a safe bet to protect your leaves from any and all flying or crawling things. 

(Learn more about how to install garden covers.)

How to Get Rid of Cabbage Loopers

If you spot signs of these pests in your garden, there are ways you can treat them organically by following these steps.

Step One

The first measure to treat your plants is to remove all of the damaged leaves and clear the soil around the plant of any debris. Search for little green caterpillars in the surrounding area and on the stems and leaves of your plants. Pick off any larvae by hand and drop them into a bowl of soapy water. Brush off any eggs from leaves.

Step Two

For the next two weeks, continue cutting away damaged leaves and cleaning the soil area. Keep careful watch for pests.

Step Three

Add some fresh compost around the base of your affected plants to ensure your plants have all the nutrients they need to fight off pest pressure. This is the equivalent of taking lots of vitamins when you're sick.

Step Four

If severe cutting and cleaning doesn’t rid your plants of the pest, you can use a number of sprays or soil treatments. Monterey B.t. is an organic product that's long been used to control cabbage looper populations. It consists of Bacillus thuringiensis, a soil-dwelling bacterium that kills caterpillars but has no effect on honey bees or birds. It's definitely one of the stronger forms of pest control out there (I prefer simpler solutions like castile soap and garlic barrier for other pests), but it's still safe to use around pets and children.

If you need to apply this treatment to your garden, you want to first make sure you dilute it according to the directions and spray it directly on the leaves using a spray applicator. Avoid spraying before a rainfall because the treatment is just going to be washed off as soon as the rain hits the leaves. Monitor plants daily after treatment.

Back when I had that serious cabbage looper infestation in my salad garden, I had no other option but to spray Monterey B.t. every other day for one week.

After you've applied any type of treatment, wait 3 to 5 days before harvesting from the plants. Make sure to rinse your produce thoroughly before you eat anything.

If you don't see pests reappear within a week, then you've most likely handled the issue.

If your plant looks worse for the wear or if the problems persist, it might just be time to pull the plant from the garden. I recently had a spinach plant that was starting to have issues. When I inspected it, I found a tiny caterpillar in the center and decided to remove it. I actually found several more caterpillars all hiding in the root system of this plant, and that’s what was taxing and killing it.

This is why it's so important to check the surrounding soil. When you remove pest-affected plants, check about six inches under and around the plant to make sure there aren’t caterpillars or other pests lurking nearby. You don't want to plant something new there only for it to have the same issue.

In the case of the spinach plant, I was able to clean the soil around the plant and put new plants in its place that are doing great. This happens sometimes—you have to say goodbye to the plant and start fresh. Don’t fret about it. It’s not your fault. It happens to the best of us, so just remove it and move on!

You'll want to throw away pest-damaged plant parts. These should not go in your compost if you have a pile or bin.

Cabbage Looper vs Cabbage Worm vs Hornworm

It can be hard to tell the difference between cabbage loopers and cabbage worms since they're both little green bugs that can grow to be about an inch long before going into their cocoons. The easiest way to distinguish them is to look at their legs. Cabbage loopers don't have middle legs, which is why they "loop" themselves when they crawl.

Some young cabbage worms also will appear a darker green with white spots and then yellow heads and yellow stripes down their bodies.

It's not super important to be able to tell the difference because these pests often appear together, like the first two horsemen of your little garden apocalypse.

Then there are also hornworms, which look similar but can grow much bigger, thanks to the alarming rate at which they digest your plants. These guys are distinguished by the diagonal stripes down their side and the characteristic "horn" (which looks scary but can't hurt you). While hornworms don't attack brassicas—they attack plants in the Solanaceae family, like tomatoes, peppers, and eggplants—you'll be made aware of their presence in a similar fashion: sudden holes in your leaves.

All these guys can mean bad news for your garden if you leave them to their own devices. Follow the steps I detailed above to treat your garden the moment you spot holes in your leaves.

Don't Let Cabbage Loopers Bug You

Take a note from my failed salad business: A little mesh and regular tending go a long way in preventing the worst outbreaks.

Head out to your garden daily to tend your plants and harvest from your leafy greens. When you remove the oldest and lowest leaves from each plant, you're making sure the soil is clear of any leaf debris, and you're encouraging new growth from the center of each plant. You can grab some leaves for your salad while improving the overall health of your garden space.

If you see anything that looks abnormal, that's a sign that you have some kind of issue, and you can now take care of this issue before it spreads. Remember, every problem starts very small. If you’re out in your garden quite often, you’re never going to have a huge, sprawling problem. It’s when we neglect the garden and don’t go out there often that problems really start to take over.

The best protection, as they say, is the gardener’s shadow. Keep your body out there in the garden, and I promise you your issues will be few and far between.

When you do have issues, remind yourself that garden pests are just a part of growing good food.

If you find cabbage loopers in your garden, take a deep breath. The cycle of life is unfolding in your very own space, however annoying that may be. Nature is doing its thing, and you're helping it by growing healthy and organic food in your garden.

Thanks for being here and helping make gardening ordinary again!