Cabbage Looper: Eliminating Trichoplusia Ni

There’s something crawling across the leaves of your arugula, and it looks like a little inchworm. It’s green, and it is snacking as it goes, leaving holes throughout your plants. There’s another on your cabbage and another one on your radish leaves. What’s going on here? Wait… is that a cabbage looper?

Destructive little pests that they are in your garden, if you don’t hurry, this little cabbage worm will eat it before you ever have the chance to taste it yourself. So today, I’m going to tell you how to eradicate this moth and its inchworm-like offspring from your yard, and hopefully, you will be able to rescue your plants!

Subscribe to the Epic Gardening Podcast on iTunes or Spotify

Good Products At Amazon To Eliminate Cabbage Loopers:

• Monterey BT Caterpillar Killer (Bacillus thuringiensis)
• Monterey Garden Insect Spray (Spinosad)
• PyGanic Botanical Insecticide (Pyrethrin)
• Harris Food Grade Diatomaceous Earth With Duster
• Neem Bliss 100% Cold Pressed Neem Oil

Cabbage Looper Overview

Types of Cabbage Loopers

There are other moth or butterfly insects from the Lepidoptera order which are commonly confused with cabbage loopers. These include the cabbage worm (Pieris rapae or Pieris brassicae spp.), 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 cabbage looper, but they tend to attack similar plants and often can be eliminated in similar ways.

But for this particular article, we’re going to focus on the actual cabbage looper, Trichoplusia ni.

Trichoplusia ni, ‘Cabbage Looper’, ‘Cabbage Moth’, ‘Ni Moth’

The term “looper” derives from the way the looper caterpillar crawls. Much like an inchworm, it hunches itself up in an arched or looped shape and then propels itself forward. Its scientific name and the term “Ni moth” both come from a pattern common on the wing of the adult brown moth, which resembles the lowercase Greek letter ‘ni’. The reference to cabbage originates with the caterpillar’s fondness for Brassicaceae plants.

It is a voracious feeder in its larval or caterpillar stage and primarily consumes leaf greens rather than stems or veins. It can bore into some vegetables like Napa cabbage or cauliflower, leaving waste behind that renders the plant inedible for humans. And it can quickly devour your vegetable garden.

Life Cycle of Cabbage Loopers

An adult cabbage looper moth lays multiple pale yellow, round cabbage looper eggs on each plant, both on the tops and bottoms of the leaves chosen. Each female can lay between 300-600 eggs in the 10-12 day adult lifespan. The cabbage looper eggs hatch in 3-10 days.

The young larvae are pale white, but gradually turn green with yellowish stripes along their back. They also start out looking somewhat hairy, but gradually lose these hairy spines as they mature. Over the 3-4 week larval stage, they grow and mature, going through color shifts and molting stages, and it is during this larval stage that they consume vast amounts of leafy matter.

They then form a pupa or cocoon, and somewhere between 4-12 days later they will emerge as full-grown adult, semi-nocturnal moths. In warmer temperatures, the pupal stage is much more rapid. They are considered semi-nocturnal because they will sometimes emerge at or just before dusk to mate and feed, but they are far more active during the nighttime hours.

Common Habitats For Cabbage Loopers

Like cabbage worms, cabbage loopers live where their food is, and that means that they can turn up nearly anywhere where food for humans is grown. However, while their diet is incredibly wide, they tend to prefer brassica-species plants to lay their eggs on due to the high glucosinolate content. They lay their eggs on both the top and bottom of the leaves of their chosen host plant.

What Does Cabbage Looper Eat?

Cabbage loopers prefer plants that produce natural glucosinolates or glucosides, and that includes nearly every cruciferous food plant. While I provided a short list in the overview, here’s a more extensive list of edible cruciferous plants that cabbage loopers prefer, both for egg-laying and for feeding purposes:

• Cabbage
• Turnips
• Broccoli
• Cauliflower
• Bok choy
• Kale
• Napa cabbage
• Garden cress
• Brussels sprouts
• Collard greens
• Horseradish
• Savoy cabbage
• Watercress
• Broccoli romanesco
• Mizuna
• Bomdong
• Kohlrabi
• Broccoli rabe
• Choy sum
• Cime di rapa
• Gai lan (Chinese broccoli)
• Komatsuna
• Arugula
• Radish
• Daikon
• Wasabi
• Tatsoi
• Mustard greens (white, Indian, Ethiopian and black mustards)
• Rutabaga

Cruciferous vegetables are not the only targets of cabbage looper caterpillars. They are also quite willing to munch on beets, cantaloupe, celery, cucumbers, lima beans, lettuce, parsnips, peanuts, peas, peppers, potatoes, snap beans, spinach, soybeans, squash, sweet potatoes, thyme, tomatoes, and watermelon.

As you can see, these little inchworms are destructive… very, very destructive. And they are not picky eaters, so you have to destroy them as quickly as you find them.

How To Get Rid Of Cabbage Loopers

So, how do you get rid of cabbage looper pests? Getting rid of cabbage worms and cabbage loopers is surprisingly similar, as is eliminating many other lepidopterous insect pests. Let’s look at some of the most common options to figure out what you should do.

Organic Methods Of Looper Control

The first step in cabbage looper control is to try to eliminate cabbage looper eggs when you find them. As they are common on both the top and bottom of the leaves, it can be easier to discover a problem with loopers than with other cabbage worms. Hand-pick the eggs off the leaves while wearing gloves, and drown the eggs in soapy water or crush them to prevent hatching.

By far, the most popular way to eliminate cabbage loopers is by using Bacillus thuringiensis var. kurstaki (also referred to as BT or BTk), a bacteria which creates poison in the looper’s gut after it’s consumed. This is available as both a foliar spray and as fine dust, and both work quite well to eliminate most caterpillars that prey on produce, including looper caterpillars. However, it should be noted that in some very limited conditions (primarily greenhouse conditions, where only the strongest of the species tends to survive), there have been cases of loopers who appear to be BT-resistant. This has not shown up in outdoor conditions, and it is a fairly uncommon occurrence.

Organic insecticides such as spinosad spray or pyrethrin spray are also quite effective against any of the caterpillar species, but they must be handled with caution. These present a very small danger if inhaled during spraying, and you should work with gloves on to keep these insecticides off your skin.

Diatomaceous earth powder is another popular method to control the spread of caterpillars and other insects. Food-grade diatomaceous earth can be spread on all parts of the plant. It is not harmful to humans or larger animals like pets, but to insects, it’s like glass… it cuts their soft skin and causes them to dehydrate and die.

Environmental Cabbage Looper Control

Using parasitic beneficial insects such as Trichogramma wasps to eliminate cabbage loopers has proved to be incredibly effective. There are some parasitic flies that also work quite well. These natural enemies of cabbage loopers and cabbage worms seek out the cabbage looper larva and start laying eggs in their soft skin. When these eggs hatch, the parasitic wasp larvae will feed on the looper.

Many varieties of birds, both wild and domesticated, will eat cabbage loopers. After all, they’re natural enemies; what bird doesn’t like a worm? Among the most prevalent are house sparrows, skylarks, and domesticated fowl such as chickens, turkeys, and ducks.

Preventing Cabbage Loopers

When looking at how to get rid of caterpillars naturally, one of the best ways that I’ve discovered is to keep them from reaching the plants at all. If you use a floating row cover over your plants, the row cover prevents the cabbage looper moth from laying its eggs on the host plants entirely. Floating row covers also prevent other pests from attacking other vegetable crops.

Neem oil is another effective choice. This oil smothers the eggs when sprayed onto them. While it does not completely repel cabbage loopers, it acts as a growth retardant when consumed, and the leaves taste bitter to the worms and slows the speed of consumption.

Another option is to use a garlic spray that discourages the butterflies from laying eggs on your plants. You can buy garlic oil sprays, but you can also make your own garlic spray.  This reduces feeding by June bugs, squash bugs, cabbage worms, cabbage loopers, aphids, and a variety of other insects. Adding a little mint or neem oil to this can be beneficial, too.

Frequently Asked Questions

Q: What does the cabbage looper turn into?

A: The cabbage looper turns into a cabbage looper moth called the Ni moth.

Q: Is the cabbage looper poisonous?

A: No, at least not to humans or our pets or livestock.

Q: What do cabbage looper caterpillars eat?

A: A huge list of cruciferous crops, as well as some related ornamental plants. They also thrive on wild plants like lamb’s quarters or dandelion.

Q: What kind of butterfly does a cabbage looper turn into?

A: They turn into cabbage looper moths, not butterflies.

Q: How long does it take for a cabbage looper to turn into a moth?

A: It takes 8-15 days for a cabbage looper to pupate and turn into a moth. The entire life cycle from egg to adult takes up to 35 days. An adult cabbage looper moth can live for at least 10-12 days after emerging from pupation (and sometimes longer) and can lay 275-300 eggs in their lifespan.

Q: What does a cabbage looper cocoon look like?

A: There’s a photo of one to start this section! The cabbage looper chrysalis looks almost like a spiderweb attached to the bottom of a leaf. The worm pupates under this webbed structure.

Q: What do cabbage looper eggs look like?

A: They are small, round, and yellowish in color. You can tell the difference between cabbage looper eggs and cabbage worm eggs because cabbage worms lay oval-shaped eggs and loopers produce round ones. Looper eggs are also more spread out rather than being clustered as cabbage worm eggs are.

Q: Can you eat cabbage that had cabbage worms?

A: If you’re not squeamish, sure! If you are squeamish, remove any portions that are particularly hole-filled and wash the rest.

Q: Do birds eat loopers?

A: Absolutely! Birds are natural enemies of cabbage looper larvae. Like other worms, they find them delicious.

Q: Do cabbage loopers eat anything other than edible plants?

A: These voracious little critters also happily munch on chrysanthemums, hollyhocks, snapdragons, sweetpeas, other Brassicaceae family members like alyssum or lunaria, and commercial crops like cotton and tobacco. Some wild plants such as lamb’s quarters or dandelions are also host plants. These are opportunistic pests that don’t stop at cole crops or other edibles.

Q: I’ve read that you can salt cabbage loopers to kill them. Does this work?

A: While you can use salt to dehydrate cabbage loopers and slowly kill them, it’s just not as effective as solutions like BT or diatomaceous earth. Salt also has potential negative impacts on your garden, especially if it builds up over time in your beds.