How to Control and Prevent Cabbage Looper

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

The answer is likely cabbage looper. These destructive little pests will eat through your entire vegetable garden before you ever have the chance to taste it yourself.

Luckily, I’m here to tell you how to eradicate this moth and its inchworm-like offspring from your yard. After this, you’ll hopefully be able to rescue your plants!

What Are Cabbage Loopers?

There are other moth or butterfly insects from the Lepidoptera order commonly confused with cabbage loopers. These include:

• Cabbage worm (Pieris rapae or Pieris brassicae spp.)
• Cabbage moth (Mamestra brassicae)
• Cabbage webworm (Hellula undalis)
• Orange tip butterfly (Anthocharis cardamines)
• 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.

The term ‘looper’ derives from the way the looper caterpillar crawls. Much like an inchworm, it hunches itself up in a looped shape and propels itself forward. Its scientific name comes from a pattern common on the wing of the adult brown moth, which resembles the lowercase Greek letter ‘ni’. The reference to cabbage originates from 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.

Life Cycle

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 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. During this larval stage, they consume vast amounts of leafy matter.

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

Common Habitats

Like cabbage worms, cabbage loopers live where their food is. That means 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 to lay their eggs on due to the high glucosinolate content.

What Does Cabbage Looper Eat?

Cabbage loopers prefer plants that produce natural glucosinolates or glucosides. That includes nearly every cruciferous food plant. Here is an extensive list of edible cruciferous plants that cabbage loopers prefer, both for egg-laying and 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. They are not picky eaters, so you have to destroy them as quickly as you find them.

How To Get Rid Of Cabbage Loopers

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 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. Drown the eggs in soapy water or crush them to prevent hatching.

The most popular way to eliminate cabbage loopers is by using Bacillus thuringiensis var. kurstaki (also referred to as BT or BTk), a bacteria that 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 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 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. Reapply after rain or excessively humid weather.

Environmental 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. The best way to encourage them into your garden is to plant floriferous plants they like. These include but are not limited to yarrow, feverfew, fennel, dill, and chamomile.

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. Among the most prevalent are house sparrows, skylarks, and domesticated fowl such as chickens, turkeys, and ducks.

Prevention

One of the best ways I’ve discovered to prevent cabbage loopers 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, slowing 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