by Ruth Gulley
Want to fight cabbage loopers? Fun Fact: Cabbage loopers are called “loopers” because they move like inchworms, making a “loop” as they bring their back body to meet the front. Loop loop loop.
Not-So-Fun Fact: These little green caterpillars (soon to be egg-laying moths) will eat all the things in your garden if you aren’t careful. Well, nearly so. Yes, they are called “cabbage” loopers, and they do prefer plants in the cabbage family (broccoli, kale, brussel sprouts, collard greens, and other brassicas).
But these chubby buggers can consume three times their body weight in a day, and they aren’t stopping with your cruciferous vegetables. They’ve also been known to chow down on tomatoes, potatoes, beans, peas, cucumbers, celery, and the list goes on.
The good news is that with a few simple steps and considerations, you can effectively prevent or halt the damage. Here’s what you can do.
Know What to Look For
There is some confusion about the difference between a cabbage looper and a cabbage worm—as well as which winged insect each comes from. While they do similar damage to crops in the cabbage family, the cabbage looper is much more destructive overall, so it’s important to make the distinction clear. In its larval, caterpillar stage, a cabbage looper is light green, its skin is mostly smooth, and it has thin white lines running down its back and sides. Oh, and it loops, remember? Loop loop loop. By contrast, a cabbage worm is a deeper green, is quite fuzzy, usually has a faint yellow line down its back, and has more of a crawl-y movement going on—no looping.
But for early detection, knowing how these critters actually get into your garden is even more important. The cabbage looper comes from eggs laid by a brownish-gray moth with symmetrical small white spots on the upper portion of its wings. The cabbage worm comes from eggs laid by a small white butterfly with black spots on its wings. There are a lot of sources on the internet claiming that the looper comes from the white butterfly. This is certainly an understandable mistake to make, and treatment is similar for both of these pests, but it’s still better to know exactly what you’re dealing with. Again, cabbage loopers will munch on a lot more than cabbage. Both the cabbage worm and the cabbage looper will lay single, rigid-looking eggs on the undersides of leaves.
To learn more about cabbage looper identification, see this website from Oregon State University on Cabbage Loopers.
Use Floating Row Covers
Using floating row covers early in the season is a great way to stop the moth-to-egg-to-caterpillar-to-moth cycle from even starting. Moths will emerge from their winter cocoons, they will be unable to lay their eggs on your plants, and they will move on. Once the plants are too big for the covers, you should be in the clear and no longer need to be vigilant against this particular pest anyway.
Manually Remove and Kill Larvae and Eggs
Sorry to get all blood thirsty on you, but seriously, it’s not practical to simply remove the cabbage loopers from the area. Remember that they are caterpillars and will soon turn into flying moths, which will find your crops and lay eggs on them. You can kill them however you want, but the least gross way is probably to bring a container of soapy water out to your garden, and drop the loopers in as you find them. Check the undersides of leaves for eggs they’ve laid, gently scrape them off, and similarly dispose of them.
Attract Cabbage Looper Natural Predators
Two words: parasitic wasps. They are harmless to humans, they lay their eggs inside caterpillars (killing them), and they probably already live in your backyard. However, you may not ever see them. They are teeny-tiny, and they are great for keeping the cabbage looper population in check. The best part—they are a major flower pollinator. So if you want to invite these magically miniscule, murderous allies into your garden, grow more flowering plants. If you can, try to have flowers around all year. Cowpea, white clover, and marigold are all excellent choices.
Conduct Biological Warfare
Here is a an oddly fascinating, though slightly morbid, option for your consideration. During the course of your struggle with cabbage loopers, it may become evident that some of them (not enough) are contracting and dying of the virus Trichoplusia ni single nucleopolyhedrovirus NPV. A dead looper that is swollen, limp, and a creamy white color probably died of said virus. Gather the infected corpses, and grind them into a paste. Dilute the paste with water into a sprayable solution. Spray it all over the infested area.
Kill Cabbage Loopers with BT
If you have a larger operation or if the infestation has progressed to an unmanageable level, consider buying and using Bt. Short for Bacillus thuringiensis, Bt is an organic and biological insecticide. When used properly, it is very effective against cabbage loopers and does minimal damage to beneficial insect populations.
Clean and Till in the Fall
If you really want to stay ahead of the game, don’t wait for spring to clean and till your garden. Cocooned cabbage loopers can stay on the undersides of dead leaves straight through the winter, ready to emerge as moths in the spring. At the very least, you should remove old plants from your beds. You can take it a step further and bury or burn their remains. Finally, till the whole thing up, and cover it for the winter. This should smother and kill any cocoons you might have missed.
While cabbage loopers can do an unbelievable amount of damage to your garden, it is totally within your power to stop them. We hope you’ll implement some of these strategies this growing season. Happy spring!