I’ve started a large portion of my brassicas (primarily broccoli, cabbage and cauliflower), and I’m about a month and half out from planting them in the garden, but this year I want to be prepared. Last year I was assailed by an onslaught of lovely little white butterflies dancing all over my garden. “Assailed… by butterflies?”… you might be asking. But let me assure you- these are butterflies that no gardener wants to be visited by. These are the dreaded Cabbage Whites. And while they may look sweet & innocent, their progeny are up to no good!
The Imported Cabbageworm (Pieris rapae), commonly known as the Small Cabbage White or Cabbage Butterfly, can cause extensive damage to cruciferous plants. The adult butterflies appear in the early spring (in warmer climates they can be active all year round) and lay eggs on the leaves of the host plant—they prefer members of the Brassicaceae family. These little buggers can be hard to spot at first- they are a delightful shade of green that blends perfectly with a cabbage leaf. But as they grow, so do their appetites, and their presence in your garden becomes obvious. Look for small, irregular holes starting on the exterior leaves of plants working their way to the center of the plant as the larvae mature. The most telltale sign of all may be the piles of frass (the less gross name for bug poop) that accumulate on and under the plants they are feeding on.
I have used Green Step II™ Caterpillar Control, a product which is sprayed directly on the affected crop and features the active ingredient- Bacillus thuringiensis ssp. kurstaki, (also known simply as Bt) with great success. Bt is a bacterium native to the soil in many areas of the world. In general, it is regarded as environmentally safe, and has little to no effect on non-target species. But when caterpillars of the Lepidoptera order gobble up Bt, they get a nasty surprise. Long story short, after ingesting Bt a toxin is released in the caterpillar’s insides that begins to break down their guts. Sounds like an awful way to die! As I said, Green Step has always been extremely effective for controlling my cabbageworm populations, but I’d like to move to a completely no-spray method of control, especially because the Bt targets all Lepidoptera, which includes critters I DON’T want to get rid of, like Monarch and Swallowtail butterflies.
I’ve had good luck using row covers, but timing is everything. I found that the adults work fast—if your plants aren’t covered within a couple days of transplanting (sometimes even within a day), the adults have already found the plants and laid eggs. Covering with row covers at this point (after eggs are laid) is basically like creating a luxury B&B for cabbageworm larvae! I’m doing all I can to encourage natural predators of the cabbageworm, including shield bugs, ambush bugs, vespid wasps and trichogramma and many insect-eating birds. I also just came across a wacky idea on the internet (the web is full of those you know) which claimed that you can deter the adult butterflies by making look-a-like butterfly decoys and placing them on and around your plants! I may have to try this just to see what happens! I’ve not tried, but read that things like companion planting, diatomaceous earth and various home-made sprays will work- but have yet to talk to a real live person who’s had high cabbageworm populations and true success with these methods.
Sneaky little larva circled in red, see how the blend in perfectly? Piles of caterpillar poo (frass) are much more obvious!
And for more on my cabbageworm control methods (as well as more detail on the 4 main types of 'cabbageworms' in my Ohio garden, check out this video: https://youtu.be/RVS-YVNVfcc