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 I’d 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 (just ordered one!) 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 butterfly, Pieris rapae, because I have also seen its adult stage flying around, a smallish white butterfly with a couple of smudgy spots on each 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.

As 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 (also effective, apparently, but synthetic and not approved for organic production) or even natural pyrethrum/pyrethrin (which is permitted for organic use). Instead, 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 the 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, I rinse off 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). I’ll be certain to clean up extra-carefully this year, to reduce the chance of overwintering pupae, and am reading up on weeds in the cabbage family (wild mustards, for instance, and shepherd’s purse, among other) with a sterner eye to their 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, but 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.

59 comments
June 25, 2012

comments

  1. Michelle Becker says

    Margaret,
    I feel a similar resistance to using even organic pest control in our gardens, BUT, I’m doing it anyway for the cabbage loopers. I hand pick many critters but the cabbage worms are just too well disguised for me to rely on my eyesight. In our gardens, the cole crops are planted in one large area (that gets rotated from year to year) and this has been a boon year for caterpillars of all kinds. I noted your recent photo of a geranium turned to lace: same here at Stonewell Farm where even the petunias and the nicotiana have been chewed through,. We’re using Dipel. It works but requires multiple applications, unless one has been uber-vigilant and eliminated all the eggs and larvae hidden in the nooks and crannies of the underside of the foliage. I’m intigued by LaDonna’s suggestion of wood ashes and wonder why this would work? As a deterrent or as a knock-down after emergence?

  2. Kathy G says

    This year I made a mini hoop-house out of remay (light wt. fiber covering) and flexible conduit. I’m keeping my brussel sprouts covered completely; works like a charm…no moths and great looking plants…. in fact the best & biggest I’ve ever grown. Yes I do open it to water the plants but close the ends afterwards so watering is a pain but worth it! Best of all,,,, no chemicals, even the ‘safe’ ones.

  3. Robin says

    I “harvested” about 25 of these things this morning. And I have been doing it every day! I’m getting discouraged.

    I have also seen a big, bright green grasshopper on the kale. I thought he might be eating the caterpillars but I guess he’s eating the leaves too.

  4. Rhonda Lawrence says

    My problems………..Something is eating my potato plants. Entire lower leaves gone, and lower stems just “snipped” off as well as no leaves. Left beer under plant, no slugs, and I cannot find anything when I’m up early in the twilight! The plants are in a large pot!
    Second problem, rhubarb leaves being devoured! (Aren’t those leaves poisonous to humans???) I put beer in tuna cans and have found a ton of small slugs, earwigs and 2 huge slugs that I think were young banana slugs (The largest was 2″ X 2/3″ maybe). I will keep putting out the beer!

  5. says

    Rhonda, you might have rabbits eating your potatoes and rhubarb. Even though they’re supposed to be poisonous, I’ve watched them eat both!

  6. Lisa says

    Great post! I just picked a few that would eating my radishes… I only plant them in the first place to keep other pests away from my beans & squash plants, which seem to be working! But I am how wanting to plant a fall harvest of broccoli & cabbage. In the spring I create a barrier with bamboo sticks covered with netting, the kind you’d use to make a petticoat from the fabric dept… It worked well in Spring as the butterflies couldn’t get to the leaves to lay their eggs, but now that they seem to be onto the radish, I am afraid they may crawl thru once hatched. Just an idea with the netting, as sunshine & water still get thru easily!

  7. Lisa says

    p.s. How can we attract the parasitic wasp? Any I love the idea of tossing the worms out to bird, will keep the house cats entertained!

  8. Rita says

    When I grew broccoli, I was amazed that when the plants grew to a certain height, the caterpillars disappeared. It took me awhile to realize that the certain height was just when the plant could support birds. ^__^

  9. Robin says

    Me again. These cabbage worms consumed many hours of my time as well as quantities of my kale! My question is, when you do finally clean up your crop, do you compost these plants? I’m worried there will be some critters that will survive into spring even in the compost; I’m not sure mine gets hot enough, especially at this time of year. If you don’t compost, then what do you do to get rid of the stuff?

  10. Dd says

    By the time I figured this one out, they had done mucho damage. Very helpful post. I’m on it for next year! I did haveli try of sprouts however.

  11. G says

    I too have the little grubbers this year. Last year my cabbages were prize winners.
    My greens were awsume and now this year, they have distroyed every cabbage plant, broccoli, plant and all the greens. I am sick about this. All I seem to be doing this year, in my two organic box gardens, is feeding the critters. Certainly not me.

    I have carrots, corn, tomatoes, peppers, sugar snap peas, spinach, organic lettace and okra left, hopefully for now, with no sign of problems. Just never expected this infestation so fast and furious.

    G
    Memphis, TN
    Organic Box Gardner

  12. Doreen says

    I just came inside from yet another daily session of caterpillar-picking. My frustration comes from the fact that I have my greens bed fully netted off with an insect barrier netting. I really can’t figure out why I have caterpillars appearing, because a) there is no imaginable way I can see the cabbage whites getting under the netting; b) I haven’t even seen any cabbage whites in the yard for over two weeks; and c) in the month I have had this bed netted off, I have not seen any butterfly stuck inside the netting. Last year, with a much less secure netting, I routinely found butterflies stuck inside after they figured out a way to get in.

    If the adults were hatching from the soil (completely new soil, mostly bagged from “reputable” sources), I would still expect to see adults trying to get out of the netting. They’re determined enough to find any crack in the netting to get in, but not to get out! Where are my caterpillars coming from??? I am so disappointed that this wonderful timesaver netting has completely failed, and I can’t figure out why. I have very few leaves touching the netting, and those leaves have been undamaged, so I doubt adults are laying eggs though the mesh–last year, I used the petticoat material for my netting, and I can guarantee the adults will lay eggs through that material, so you’ll want to be sure you don’t have leaf-mesh contact.

    I’m trying BT again–it seemed to work a couple years ago, and it seems like the only viable option for me right now. So far, I’m not seeing great results, but I may need to purchase new BT concentrate. Unfortunately, it doesn’t work on leafminers….

    • says

      How discouraging, Doreen. I always manage to squish enough eggs and new worms that I stay ahead of it, but I am pretty ruthless (every morning at dawn on patrol).

    • says

      Hi Scarlet. Well, truthfully, i just do it between my thumb and third finger. (Gross, right?) A garden friend I work with sometimes simply uses her pruner to cut them in half (as she does slugs). Also gross! (But you asked, so I answered.) Easier on many people’s stomachs: take a small pail of water or soapy water out with you and simply drop everyone in.

  13. Mary says

    Hello! I’ve notice those same green worms eating my cleome spider flower leaves. Some I started from seed didn’t make it. They ate the whole thing. Now they are trying to eat the larger ones. I knocked them off with a small stick and killed them. I like the soapy water idea. I’ve not had this issue in the past with them. They are trying to take over, but I plan to win!!
    Have a good day!
    Mary

  14. Betsey says

    Hello Mary, I, too have been plagued with cabbage moth larvae. Will you or have you pulled the plant out? I am at a loss with what to do since the leaves are so far gone and they have gotten to the small cabbage that was forming after so much care. If I cut it down will it start regrowth? I did cut down my collard green plant after it was also chewed upon. That was over wa week ago and no regrowth……Any help would be appreciated. Thanks and happy gardening!

    • says

      Hi, Betsey. I have not had them get to that stage so far, but when they once attacked young plants I did pull the entire thing, root system and all, yes, and destroy it (not putting it in the compost near my garden, but I put it in the woods nearby). I don’t think of collards and cabbage as “cut and come again” in July, no, so I think you are better off sowing fresh seed now.

  15. Roy Ashton says

    I think you may be over reacting butterflies are beautiful to have in your garden, lets not kill them. Pick the caterpillars of the leaves and put them in an open box with old cabbage leaves ect.

    • says

      Hi, Roy. The cabbage white butterfly of which the cabbage worms are the larval form are an accidentally introduced pest to the American landscape, and extremely plentiful and widespread. The reason I squish the caterpillars (rather than spray even an organic caterpillar solution like Bt) is to affect this pests ONLY, not harm other Lepidoptera in their larval stages. Very important to be targeted in our pest control, I agree.

  16. Mary Brigode says

    Margaret, This is my first year experimenting with Brussel Sprouts. They were growing beautifully until a couple weeks ago, the bottom leaves were attacked by something and died quickly. I pulled them off to keep from spreading to higher leaves. Will this keep those tiny sprouts by those leaves from growing? Should I have left the leaves? Thank you

    • says

      Hi, Mary. I’m assuming you have some leave left so the plant is fine other than having lost the bottom row or so? By this time in the season that should be fine. My plants have only tiny beginnings of sprouts at this point — not a good sign! — when usually the sprouts are of decent size in the fall already. We have had a crazy weather year here. Be sure to check daily for other pests, many of whom eat from the top down (so check the terminal bud or topmost growing point).

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