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.
When that broccoli does appear, just remember to soak the heads you have picked in a strong salt solution for a bit, You might just be surprised at who you will find hiding inside tht floats to the top of the salt solution. Rinse well before cooking for a truly vegetarian dish.
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I’ve been struggling with these guys eating my kale for a couple years now. they are masters of disguise, for sure. I’m too squeamish to squish, so I throw them in the yard for the birds…but don’t know for sure if that’s a great idea.
PS, why do you choose not to use the b.t.?
Yep, pretty sure these are the same critters responsible for mowing down my mustard greens and making swiss cheese out of the collards.
@Robin – Have you had good results with b.t.?
It isn’t the bugs in my garden that are a problem – it is the rabbits. They do a lot of damage FAST. And the cats don’t seem to realize they are mortal enemies and should be in hunting mode.
Those things are such a scourge! I have given up on growing broccoli because of them. They are impossible to find in the broccoli florets! They do, indeed, do a lot of damage fast!
I considered sprinkling the plants with foodgrade DE but have just never gotten there yet. I do believe it would work. Spraying with water in which I have boiled my organic tobacco or rhubarb leaves would also work but that’s broad spectrum so I am reluctant to use it. It’s impossible to grow brassicas with out doing something about the green caterpillars.
I hand picked the sawfly larvae off my 2 doz hibiscus plants last year and the rose chaffers off the roses. It’s a very time consuming chore but it does work!
Once upon a time, I used milk soured with a little vinegar to protect my cabbages from these pests. (Can’t recall where I found that idea – maybe an ancient copy of Organic Gardening.) Just pour it over the heads. Then keep an eye on your pets – my dog ate a whole head of cabbage after I treated it.
I’ve have tiny white flies on my brassicas, and I was expecting the little green worms since the cabbage butterlies were all over the place. Perhaps I must missed the worms because some of the leaves of my kale were nippled right down to the stem. Last year I had the worms and picked them off and literally threw one right into a robin’s bill.
We’re also dealing with these but they pale in comparison to the damage caused by the two adolescent woodchucks that shimmied through the fence. I cannot believe how easily something that big can fit through an opening that small. Let me tell you, those little guys can eat. We’ve spent the last two days reinforcing our 2″ x 4″ welded wire perimeter fence with a layer of 1″ chicken wire.
With this done, the next morning, they tried to dig under the gate barrier. I spent yesterday setting a 2′ x 4′ blue stone threshold pad. They’re impossible to trap, they’re too well fed to bait into a have-a-heart. Reasoning with them is out of the question. How do you deal with these? I really don’t want to do them in.
On the bright side at least it rained last night.
Hi, Aaron. You will have good results with the b.t. if you follow the directions.
@Robin — You know, it’s no really rational reason. I have just grown weary of all the “safe” things turning out not to be, and reading about organisms that develop resistance to various substances (as some diamondback moth caterpillars have, I believe — speaking of a pest of cole crops), and frankly just the whole thing of spraying/buying products to fight this or that/etc. I guess it all exhausts me these days — how little we really know. Also, I don’t wish to kill other than the specific pest that is troubling me. I should have set up the fabric tunnels higher (so they could stay on) and just left it at that, and as I say when I saw the butterflies, I should have put an end to it right there, as I did with beetle eggs on the undersides of early-rising potato leaves. That nipped that in the bud. In a smallish garden, vigilance and mechanical approaches (fabric covers, hand-picking…) seem most comfortable to me right now, but years ago I did use b.t. and as I say it is approved for organic use.
@ Aaron, I used b.t. a few years ago on brussels sprouts and broccoli, and I think it helped but I also grew tired of doing it (mixing up the stuff and spraying it with the hose contraption) and then I think you have to re-do it after a rain, and I wasn’t 100% comfortable with the chemical idea even tho they say it’s safe…I don’t grow either of those things any more because the end results weren’t worth the labor or space in my limited garden.
Kale though, I’d like to keep growing. I’ll probably try to be the vigilant picker-offer still…
I have to agree with you about using even more “natural” pesticides. If we let the pests thrive (albeit with a little squishing on the side) their natural preditors are going to start breeding up in number and will eventually take on the role of natural pesticides. It’s too easy to reach for that bottle of poison when we are ultimately doing our gardens a HUGE disservice. Waiting is not easy but hugely satisfying when you see a ladybird larvae eating its weights worth of aphids, a lacewing larvae scoffing white fly and native wasps zapping your caterpillars…nothing more satisfying than that! (Apart from a good horror movie that is… lol)
I don’t do a lot of cabbage family at the moment – but two years ago the same buggers you have were munching four magnificent brussels sprouts plants. I did a lot of handpicking, and some of the sprouts were a little munched, but at least they don’t hide the bugs like broccoli. I did not find that there were many predators of these things. I gave a lot of them away – four plants was a lot of sprouts! No one seemed to mind the nibbles….I will use covers the next time.
An interesting article on prevention from 1877, urging folks to put children to work with butterfly nets!
So far I’ve been getting by with handpicking the few worms that I’ve found. I have seen some spiders hiding on the backside of the leaves and wondered if they have been helping my cause. I’m also lucky enough to live in the middle of the woods, a bird paradise, and I’m sure they are helping, too. My birds are a big part of the reason I hesitate to use any chemicals, organically approved or otherwise, There are hungry nesting bluebirds just 10 feet from my garden.
About woodchucks, they are a nightmare. They not only demolished all my cauliflower and broccoli last year, they have dug heaps of gravel out from under our front porch. While I realize it’s not ideal and certainly won’t work for most people, we finally resorted to an electric fence this year to keep the gravel in place and the veggies safe at least from woodchucks. So far it’s working. I just have to remember to unplug it each time I go outside.
For the first time this year I had cabbage moth caterpillars on the early lettuce in my greenhouse! There were no cole plants around yet, I guess. Also, we have had bad woodchuck damage in the past, and we have also found that the only effective deterrent is an electric fence.
Hi, Mary. Woodchucks are my most-loathed nemesis. Fascinating that the cabbage caterpillars pestered you even in the greenhouse. Sorry. See you soon here again, I hope.
My 3 year old grandson and I just use the pick and squish method. Had a bumper crop of the worms this year! (as well as rabbits!) But the broccoli still tasted wonderful! Good luck everybody!
They are cabbage worms — we had them in droves last year. My husband has what I call “hunter’s eyes,” could spot them in a minute and had no qualms about squishing them. The real hoot was watching and snapping (do digital cameras snap?) some shots of wasps turning them into dinner for the brood.
http://www.lettherebegarden.com/2011/07/wasps-as-good-guys.html
I suspected said nest was the one in the hose trolley — when I was foolish enough to disturb it one day, I was chased halfway across the yard, screaming, “Don’t you threaten me, I feed your children!”
Between husband’s eyes and and wasps’ grocery list, the worm population was controlled to the point where they didn’t affect the harvest.
I used to have a woodchuck problem. But a couple of years ago I got a McGregor fence. It’s a low electric fence that runs off a single 9 volt battery. And it really keeps all the small animals out of the vegetable garden.
Hi, Tricia (and Bill). Love your tale of fighting off the invaders. :)
How are you, Elaine. Your grandson can stop by here ANYTIME. He is already a great gardener, apparently.
I know it’s not practical for every gardener, but ever since I started keeping dogs around, I’ve had no problems with deer or woodchucks. The first of the dogs was a fierce Kuvasz; the current minder is a Border-Collie / Cattle Dog cross. We’re surrounded by 100s of acres of forest on one side, and there is a multi-generational family of groundhogs burrowing in an around our cleared acreage. None of the critters make it close enough to the garden to do any damage, as the dog is free to be on constant patrol (except over night).
There are many days I wish I had a dog (don’t tell my cat, Jack!) for just the reasons you describe, GG. I am in a giant state park as well and the wild-things population is insane. Nice to hear from you and hope to see you here again soon.
Electric fences are 100% effective against woodchucks, in my experience. The fence can connect to an extension cord or it can be powered by a battery. For a woodchuck you set up a low fence with 2 wires, one about nose level to the animal and the second about a foot above the ground. The shock from the battery-powered fence is mild to a human, but the woodchuck learns and stays well away.
Ugh, I am having the same problem. I’ve adopted a laissez-faire attitude (mostly due to lack of time for hand-picking) but I do agree that no chems is the way to go. It’s a shame because the cabbage is such a beautiful plant; I’d grow it ornamentally in my herbaceous beds if the buggers would leave the leaves alone…
Thanks, Brian — I have been thinking electric lately myself. Good to have your 2 cents.
My Mom would dust with wood ashes on her cabbage, squash and cuke plants. After a rain it was my job to replenish the ashes. It must have worked or she would not have bothered since she was very busy. Is there any reason this is harmful to humans? Of course most of us no longer have wood cook stoves for ashes but we do have those fire pits in our back yard. I realize ash can create an imbalance in the soil but she used small amounts.The wood came from our own trees not from any treated lumber scraps.
Crop rotation and interplanting with herbs seems to work the best for me. I also plant my brassicas in the fall instead of the spring, when the critters aren’t out as much (and seem to be discouraged by wind and cold temperatures).
Last fall I planted cabbage and kale in the front, this year I’m planting pak choi, kale and cabbage in the back. In the spring I put butternut squash in the front where the cabbage was and sweet potatoes where the kale was. My cabbages in back promptly bolted, but nothing has touched my kale and pak choi so far.
*keeping fingers crossed*
*usually* I plant in the fall … this year I’m doing an experimental garden in back and couldn’t resist …
Good ideas, Pat. Thanks for chiming in.
As an expert in this field, I want to make sure everyone knows the distinction between B.t. and pyrethroids. B.t. is a naturally occurring bacterium, commercialized more than 50 years ago and is the most successful natural product for insect control to date. It is ultra biodegradable and proven to be low risk. Resistance has occurred only once or twice in this 50+ year history – in Asia where they oversprayed – daily- and hence selected for resistance. Using Bt in the garden judiciously when needed will not cause resistance.
Pyrethroids are NOT natural products. They are the synthetic versions of the natural plant extract pyrethrum and have been changed substantially from the natural extract so that they are more toxic to pests and more persistent in the environment, hence they are being restricted because they affect aquatic life in waterways. The natural pyrethrum is ultra sensitive to UV light and is degraded in a few hours, unlike the synthetic pyrethroids.
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?
Thanks, Pam — and I meant to distinguish between synthetic pyrethroids and Pyrethrum (and I use neither). I have clarified it in the copy thank to you, even though the natural ones (like the b.t.) are OMRI approved. I would add that even with the natural Pyrethrum that you want to use it according to label directions and not be careless — it’s still an insecticide. Sometimes people equate natural or organic with “nothing to worry about” and many of these products still bear a “Caution” label, so we need to respect them if we use them.
Hi, Michelle. As I say, I am tempted. After this year’s decimation of so many things I may give in on the b.t. I just hope the birds are enjoying all these juicy little creatures and having some delicious snacks on some of them… :)
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.
I am jealous, Kathy G.,and dreaming of a hoophouse myself. A friend’s husband made her one recently and I might have to hire him…
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.
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!
Rhonda, you might have rabbits eating your potatoes and rhubarb. Even though they’re supposed to be poisonous, I’ve watched them eat both!
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!
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!
Thanks, Lisa. Great idea — I keep forgetting about “petticoat” material. Great plan.
Hi, Lisa. Wish I knew. Will do some homework, but basically we need to attract the thing (insect) they wish to parasitize, right? :)
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. ^__^
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?
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.