Cabbage looper (Trichoplusia ni) on a green and red succulent leaf.
Learn how to identify and control cabbage loopers in your garden
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A few ragged holes in your broccoli leaves may not seem like cause for alarm, but it’s a different story when those holes appear in your cabbage heads. For those of us who like to grow brassicas like cabbage, broccoli, kale, and cauliflower, as well as leafy greens, these insects can spell trouble. Learn how to ID cabbage loopers and what to do about them.
What are Cabbage Loopers?
Cabbage loopers are a common garden pest and are primarily a problem in brassicas, especially as their name implies, in your cabbages. The caterpillars are leaf munchers and can leave ragged, irregular holes in leaves, bore tunnels into your nicely headed cabbages, and infest your broccoli heads with frass ( a fancy name for insect poo).
The cabbage looper, Trichoplusia ni, is actually native to the US. Although they cannot overwinter in northern areas, the adult moths will migrate north in summer to lay eggs in your veggie patch.
Cabbage Looper Life Cycle
Like other moths, they go through four stages: egg, larva, pupa, and adult. It’s the larvae or caterpillar that causes the damage. Cabbage loopers are in the caterpillar stage for 4 to 5 weeks before pupating, emerging about two weeks later as adult moths ready to lay eggs and start the cycle over. Larvae hatch from the eggs in 3 to 6 days.
While the name implies they eat cabbage plants, which is true, they’ll also bother other plants in the veggie garden, especially leafy greens, all brassicas, and even some ornamental plants. Most damage is done in late summer to early fall in northern climates, as the adult moth must migrate north before laying eggs. Damage will begin earlier for southern gardeners.
How to Identify Cabbage Loopers
Green caterpillars aren’t exactly rare in the garden, but the cabbage looper is not the same thing as the cabbage worm. It has a unique way of moving, similar to an inchworm. It will hump up or make a loop in its body in the midsection. When humping up their midsection, the tail end comes forward while the head stays put. They then scoot their front end forward to lie flat again and repeat the process. Watching them move, you could say hunch-scoot-hunch-scoot.
Cabbage looper caterpillars are normally a light green (they blend in well) with a whitish strip down the side. They have three pairs of legs at the head end and several more near the tail, but no legs in the middle. As leaf-devouring caterpillars go, they are not large and are typically about an inch long and thinner than a pencil, although the last stage will be about an inch and a half.
Cabbage looper eggs are quite small, round, and creamy white or pale yellow. They are normally laid as single eggs but may occasionally be in a small cluster. Commonly, several eggs will be near the leaf margins, close to each other but slightly spaced so they are not touching. One adult female can lay several hundred eggs, which hatch in 3 to 6 days.
Adult cabbage looper moths are brown and mottled and hard to see unless they sit on a leaf. Their camouflage is very good. They’re nocturnal and fly around at night, and are attracted to the color white. You may be able to see a very small white figure 8 shape on the middle of the front wings. They completely differ from the common cabbageworm moth, which is a pale white moth with several spots on the wings.
To me, an adult cabbage looper moth looks like a few pieces of old, shredded brown leaves. They can sometimes be found napping during the day on the underside of leaves. Depending on the climate, several generations of cabbage loopers per growing season are possible.
Identifying Cabbage Looper Damage
Besides the caterpillars scooting around, look at your brassicas and other plants for irregular-shaped holes in the leaves. Of course, if you catch them in the act, you’ll see the little green caterpillar and the hole.
- Look for tiny whitish-yellow eggs laying on leaves, often in clusters of 6 to 7. Of course, if you find eggs, remove them.
- Look for smaller cabbage looper caterpillars on the underside of lower leaves. Called the “first instar,” they will scrape the surface and may not quite pierce a tough brassica leaf, but the damage is still there. A hole in a cabbage head is worth investigating. Early-stage caterpillars may leave damage that looks see-through, like a window.
- As the caterpillars grow (“later instars”), the holes will get progressively larger. Cabbage looper holes will typically be between the veins and midribs of the foliage.
Andy Wilcox
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