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 article from Missouri Botanical Garden 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 (there is a photo of their eggs on this page the Missouri Botanical website, at the bottom of the page). 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.

  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. Peggy 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?

    1. 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!

    1. 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?

  10. Peg says:

    We have maintained a couple of wren houses near our garden for many years. The nesting birds do a very good job of cleaning up bugs and worms of all kinds naturally.

  11. Nancy says:

    I too have hand picked them and as I set them aside for disposal my new kitten found them and ate them all. Eventually it became a morning ritual as I searched for more, she would come running and wait at my feet for her treats.

  12. Janet Chen says:

    Well I did use BT once, early on, and it saved what was left of my kale, only to lose it a few weeks later to a groundhog. Thank God for my CSA.

  13. Chris says:

    One year we had a yellow jacket nest that was [rettu active (several per minute existing and entering the hole) and decided to flag the area in our upper yard and leave it alone, merely on principle. We could do so because we don’t have a dog and it was not near an unavoidable human traffic pattern.. Meanwhile, at least 60 feet away I would say, I picked of a couple cabbage worms early on, and then saw nothing for the rest of the summer. I was pleased to discover in my reading that yellow jackets eat cabbage worms. I wondered what they were hovering around the kale for! Their diet early in the season is protein, and it is only late in the season that they become much bigger fans of sugar sources. It was a truly impressive demonstration of the fact that if you work with nature, nature will work with you.

  14. Mariele says:

    I only have a few kale plants, since I do container gardening along my driveway in containers made from old doors lined with plastic. However, I have had many cabbage worms and squashed plenty this summer. I covered on of the plants with one of those “bags” you use to rinse greens – to deter the butterflies. I remove one from one of the Kale plants today and found a tiny tree frog clinging to the stem. He did not even move when I moved the leaves, and he was there at the end of the day. What’s up with that ? Did he eat the worms or the worm nests, or does he just like it there? I am so thrilled I even have tree frogs and toads now, since our whole yard had no living things when we moved in 12 years ago. All spray and spray. Our neighbors are still doing it, but our yard seems to be getting ahead. Even found a painted turtle on the lawn a couple of week ago. Go turtle!

    1. margaret says:

      Nice to hear, Mariele. I love coming across all these creatures in odd spots. I had a gray tree frog in one of my bird houses this spring, even. I haven’t sprayed in 30+ years here (don’t know if the people before did so).

  15. Heather says:

    I find the only way to control them is with BTK and dusting with Diatomaceous Earth… unfortunately every time it rains you have to reapply. I did net a bunch this year with great results, but takes a lot more setup time.

  16. Judy says:

    This is the first year in 45 years of gardening here that I didn’t have cabbage worms. Two possibilities: bluebirds raised 3 broods in a box beside the garden, and they were constantly flying to the garden and back to the box to feed those hungry babies. Second idea: I sowed seeds from a wildflower packet near the brassicas, and wonder if the varied smells confused the butterflies — we did see lots of cabbage moths flitting around, but no green caterpillars.

    That’s the good news. The bad: after the last bluebirds fledged, I started seeing holes in kale, amaranth, broccoli and Brussels sprouts. But I didn’t see green worms or their excrement. Most plants were beyond saving when I finally discovered the culprits — a caterpillar I’d never had before, the cross-striped cabbageworm. They were only on the under surface of leaves, not in the buds, and I didn’t see “poop”, so they happily multiplied so much that we’ll have no fall greens or brassicas this year. A word to the wise for next season: watch out for them! They are beautiful but deadly.

  17. Judy L White says:

    The cross-striped worms decimated all my brassicas last year, especially the kale which has not usually suffered much from the green cabbage worms, so I had decided to forego all brassicas for a year; that plan has worked with other pests like bean beetles in the past. But now that it’s seed catalog season, I might weaken, if I could find a kale and a broccoli variety that the 3-striped guys don’t like. One person mentioned red Russian kale. Did that repeat the following year? Any other suggetions? I hate the thought of a year without kale or broccoli. (I’m wondering if I plant only spring broccoli, not fall, that would work?)

    1. margaret says:

      Hi, Judy. Thorough fall sanitation — getting rid of all remaining Brassica debris — is recommended and on the New England Vegetable Management Guide website if you scroll down to the entry for this pest you will see that two forms of BT (Bacillus thuringiensis), including the brand name Dipel, which are nontoxic biological insecticides aimed at caterpillar control, are recommended — key to those is spraying at night or very early morning before feeding begins. (Most of the other recommendations on that page are chemical substances you will not want to mess with!)

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