caterpillar alert: who’s eating my cabbage and broccoli?

THINGS WERE GOING SO WELL. Even the most-vulnerable crops—the crucifers, or Brassicas, including cabbage, Brussels sprouts, broccoli, kale, collards—were looking beautiful. Big, strong plants grown under row covers for about six weeks (successfully defeating flea beetles, at least) are suddenly under attack by small, velvety green caterpillars. What’s up, and what can I do about cabbage “worms”?

Though I cannot see without a hand magnifying lens if they have the requisite tiny markings, I’m betting from its overall appearance and velvety surface that this is the larval stage of the cabbage white butterfly, Pieris rapae, because I have also seen its adult stage flying around, a smallish butterfly with a couple of smudgy spots on each white wing.

This fact sheet (a pdf) from Ohio State University Department of Entomology is extremely detailed on my latest visitor, also known as the imported cabbage worm, and other pests of cabbage relatives, including cabbage looper and the caterpillar of the diamondback moth. The latter two caterpillars are smooth, not velvety, among other clues to differentiating among the three.

thecabbagewormsAs with all caterpillars, these can be controlled with the non-chemical biological control called b.t. (Bacillus thuringiensis), often sold as Dipel or Thuricide, but I don’t use it (tempted!). Nor do I use pyrethroids, which are also effective, apparently, but synthetic and not approved for organic production, or even natural pyrethrum/pyrethrin, which is permitted for organic use.

Instead, with my home-garden sized small number of plants, I’m making the rounds early and again late each morning, and hand-picking the sticky little beasts and—yes—squishing them. The challenging part is how well-camouflaged they are, often resting on leaf midribs as if they’re part of the plant. Go slowly, looking on top of and underneath each leaf; some will be tiny, just hatched.

After picking the pests, I rinse the plants, since the appearance of fresh tiny drops of gray-black excrement will signal the next time if, and perhaps just where, the hungry caterpillars are chewing. I wish I had left my row cover in place, to prevent the butterflies from laying eggs on the leaf undersides, or checked the undersides of leaves for eggs when I saw the butterflies; live and learn.

I’m putting out a welcome sign for various species of wasps that target and parasitize these unwanted caterpillars (all detailed, with drawings, in the Ohio State pdf factsheet). Most important: I’ll be certain to clean up extra carefully this year, to reduce the chance of overwintering pupae. I’m also reading up on weeds in the cabbage family (wild mustards, for instance, and shepherd’s purse, among others) with a sterner eye to removal.

The bad news: The imported cabbage worm will have multiple generations each season, so I guess this routine will become a familiar one. I don’t even really mind if they eat the tough outer leaves of the broccoli or Brussels sprouts plants. Somehow I don’t think they’ll respect any such boundaries, and are probably already eyeing the buds-to-be of the parts I’d hoped to serve up for my supper later this season. Damn.

Cross striped cabbage wormsP.S.–I’ve also been host to cross-striped cabbage worms (above) on occasion. More about that Brassica pest in this story.

84 comments
June 25, 2012

comments

  1. Emily Brees says

    Hi Margaret,

    In the 2 years I have been gardening, each year the cabbage loopers get to my kale and broccoli. Besides the consistent use of row covers, do you have any advice on companion planting to trick those little white butterflies?

    Also, would love your opinion on applying nematodes for the slugs and squash borers.

  2. Liz says

    One year my neighbor had several partridges that did a wonderful job keeping my cabbage clear of pests in spite of startling me several times as they emerged from under the brassica leaves. I always soak my broccoli, kale, etc. in a strong salt solution for a bit before rinsing and preparing for the table. It drives out the beasties and prevents a non organic surprise on the dinner plate.

  3. Sheri says

    I turn my 3 kitties out to the garden, because they were chiming collars they never get a bird but they love to catch these cabbage butterflies!

  4. Carole Clarin says

    My 9 year old granddaughter, in Raleigh NC, grew a cabbage plant for a school project. Of course the climate south of us is so different that this started while we still had patches of snow on the ground. I was there at the time of the hungry caterpillars and very large leaves were present, but before the actual cabbage formed. It was a wonderful project and my granddaughter ate cabbage for the very first time! I will pass on this information in hopes that she will try growing it again.

  5. says

    Our most successful beat so far had been the year we planted millet next to the long brassica row. ( we grow about a hundred kale plants, 60 broccoli, 30 cabbages, Brussels sprouts and cauliflower ). Birds came in for the millet and swooped into the next row to harvest the catepillars.
    This year we were out with out butterfly nets frequently catching them, and so far we haven’t seen the cabbage worms yet. We will keep our vigilance up though, it pays to keep your eyes open in this game……Peggy

  6. Melanie says

    One year I planted fall garlic and left spaces for kale — this was the ONLY year I didn’t get cabbage worms on them. I so hate them that I didn’t plant anything from the cabbage family this year (our big loss as they are all delicious). It is just gross picking them off, salting soaks and even with that when you blanch them for freezing you get so many worms floating. I like the millet and bird idea – maybe next year.

  7. Terry says

    They are real terrors on my broccoli. Every morning I pick and pinch. Kind of do the squoosh behind my back so I don’t see it. Out of sight out of mind. The big ones make a nice little pop.
    They always seem to be hiding in the heads after I harvest them so make sure you rinse and knock the heads on the counter to loosen any hiders.

  8. Pat says

    Hi……..I Hate these pests. Don’t know if this was just a fluke, but last year I planted Russian Kale along side my collards. I had nary a hole or a worm on my kale. YEAH :) but my collards looked like sieves. I didn’t care because what I really wanted was the Kale.

    This year I planted the Tuscan Kale and no collards and some of my kale looks like swiss cheese. So now I have to do the worm crush, yuck. I really like the idea of the butterfly net and catching the butterflies before they get to land in the garden.

    Anyone else ever have this kale/collards experience?

    • margaret says

      Very interesting, Pat. Using “trap crops” (planting something tasty to attract insects away from your desired crop) is a tactic used by organic farmers, in particular, but usually it’s at a bigger distance, not side by side, I think. I have not read that collards are more appealing than kale, so you’d have to try to repeat your experiment a number of times I guess to know if it’s a reliable way to outsmart the caterpillars. Over the years I’ve had them try every brassica, but not always on all at the same time.

  9. Mary Beth says

    One of my most satisfying moments gardening so far this summer has been watching a parastic wasp enjoying a meal of a cabbageworm. Hate those darn things!

    • margaret says

      Lucky you (and unfortunate cabbage worm), Mary Beth. Fascinating when we happen on all these checks and balances at work in the garden, right?

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