Bt for cabbage worms: safe to use?

Cabbage worms have really done a number on my brassicas. This is my first time trying to grow broccoli, cauliflower, and cabbage and it's been extremely difficult due to the worms. I've been picking them off by hand and spraying out the eggs with water, but they just keep coming back. They even infected my starts that were out on the porch hardening for a few hours! I talked with numerous gardeners and everyone- even the farmers at the Farmer's Market- use Bt. I am envious of their giant cabbages, prolific broccoli plants, and fluffy white cauli curds. My plants are still making up for so much lost time regrowing their eaten leaves.

So, my question is, what are the cons of Bt? Is its safety in question for humans? Do I need to thoroughly wash my vegetables before eating them once they've been dusted? I know that it targets certain insects and not a whole host of beneficials as well, so that's good, but I still worry about its effect on the ecosystem. I would love to hear from others that are against Bt use- why and what do you do instead? And from those that use Bt- how were you convinced of its safety?

Thanks!

I dont use Bt. If you wonder if it is 'safe', read its 'safety sheet'. Not exactly kid friendly. All the local 'organic' farmers use it here, it is just a mask to coverup their shortcomings as vegetable growers. Poison is poison, it leads to dependency not solutions. I always encourage people to find a better way.

They key to awesome brassicas, especially cauliflower (the most challenging), is tremendous soil fertility. We are having an exceptionally large cabbage moth year here in my valley. But in the beds that are loaded up with years of Biodynamic compost, coupled with foliar feeding of liquid fish and kelp, the damage is minimal. A little bit of bug impact is not problematic to yields by any means. The big heading brassicas are really the greatest test of your soil fertility, they dont lie. Maybe take am Albrecht soil test (gasp), to see just how close you are to optimal fertility. Build success in the garden from the soil up. Bt is a perfect example of how 'beyond organic' is the way to go.

Well, I got some spring broccoli, my cauli is heading now, my cabbage is attempting to catch up, and my spring kale is enormous and prolific. I hope these things speak for the fertility of my soil.





I think my issue thus far has been mostly the long, cool spring that stunted many of my plants. By the time they started really growing, the moths were out, doing their damage. So the stunted growth coupled with the constant need to regrow eaten leaves has made them struggle to produce. Next year I will put things out a bit later and cover them to prevent the stunting and maybe they will be able to handle the moths better. But now that it's full on summer and full on moth season, I need to figure out a solution for my fall brassicas. Thoughts?

thanks for the pics, but where is the serious damage? can you take a few pics of the ugly ones?

the plants look allright, but I think a little under fertile. by the time your cauli and broccoli start heading up, you want a plant that is absolutely massive. dont take it personally, i dont mean it that way. if this is your first year growing these crops, you're on the right track. cauliflower and broccoli are not easy vegetables. fwiw, the cool weather is generally what they prefer, so i doubt that is the problem for their lack of vigor. did woodchips get mixed into the soil at all when you mulched? that is a frequent cause of nitrogen deficiency, as the soil microbes use all the available nitrogen to metabolize the woody carbon.

just say no to poison

Yeah, I haven't taken any of the serious damage... several of those plants simply didn't make it. But you can see around the cauli head that the new leaves are damaged- the tops eaten off- and the larger leaves not shown are full of holes. I put my cabbage and broccoli out in March and we had several below freezing temps after that, unfortunately. The cauli was put out later. But most of these transplants just sat and sat and sat and did basically nothing. Then the weather turned and they started to grow and then the moths came. So I think their small size is due more to the stunting than the fertility, but I can't be sure. It could be some of both. I did fertilize with coffee grounds and pee many times to try and kick start growth. I know that wood chips mixed into the soil can cause some N deficiency, but the chips are really only on the surface. I read the study that showed surface wood chips did not cause significant levels of N deficiency, but did benefit the soil in other ways, so I went that route this year. There was also a sporadic cover crop of clover, field pea, and rye grass under the chips. Thanks for the encouragement, though! I will definitely keep trying.

Oh, I did take this pic....

Best thing for cabbage worms is to control the moth population, cabbage-worms are a type of moth larvae,
this can be done by adding in a bat-house, a single bat eats 1000+ night-bugs a night,
a fully occupied bat-house can have hundreds of bats.

It's a long term organic solution. can also make use of the guano for fertilizer,
can collect it under the bat house.

Also you'll be doing a good deed for nature (assuming you don't use much any pesticides/herbicides),
since bats are lacking habitat and so are dwindling while their prey is going rampant.

The only two games in town for commercial organic growers are bt and floating row covers. For the home gardenet, the eight year old with a badminton racket and instructions to kill all ugly green butterflies come intio their own. Collard greens can be a catch crop.

Bt is a toxic chemical.

I would not use it. Not dead.

I never had any big problem with the cabbage worm. The key is both having a fertile soil and doing a lot of intercropping.
Do not plant rows of brassicas, just mix them with other vegetables, flowers like calendula and tagete. and garlic and spring onions.

Also your garden seems a bit sterilel (my humble opinion), all those wood chips cover, no life above it, and a big space like that between the cabbages. Nature is not like that. Things grow way close to each other in a mass of green and different species. Do that, and you will not get any cabbage worm, or only very little of it.

I live in a rural area where cabbage worms abound. Lots of those white butterflies around the garden areas in my region. So I have to deal with them if I expect to get broccoli, cabbage, etc. I find that just having fertile soil and fast growing plants doesn't handle the problem. By the way, the Cabbage White butterfly is active during the day, not the night, making bats an ineffective controller.

I find that the bt for cabbage worms to be very effective and safe. it s not a poison but rather a naturally occurring bacterial disease affecting caterpillars. I find that I need to use it weekly once the plants start to show damage and the butterflies are still active. I don't need to use it constantly. I just keep an eye on the garden and watch for activity. Bt appears to stay effective for about a week. So if you are concerned about its safety, just wait a week or so before you harvest your veggies.

I also have severe pickleworm moth problems here, and caterpillar bt controls them too.

One of the reasons homemade "bug juice" controls cabbage worms is that since the bacteria is a natural disease of these pests, a sick caterpillar or more are getting ground up in the homemade bug juice preparation, thus infecting the caterpillars that you are spraying with it.

One more thing. Bt takes a few days to kill the caterpillar but it doesn't eat once it's infected. So you might mistakenly think that the bt isn't working, but it is. Just give the worm a few days to starve to death.

...Su Ba
www.kaufarmer.blogspot.com

Su Ba my growing area has the same conditions. I sprayed with BT my first year growing crucifers, but then read that BT is bad for our intestinal tracks. My soil is excellent. I solved the problem by planting Catmint near crucifers, including kale. Look into companion planting! The scent of the catmint confuses the cabbage butterflies, and they hover, and then go elsewhere. Very effective. Other mints work, too, but catmint doesn't spread and become a nuisance. Floating row covers are also effective, but involve additional cost and storage. The catmint is perennial. I find it is a lot less work. Since I replenish my soil annually, (I grow my own) I don't worry about planting crucifers in the same area. However, if you must rotate your veggies each year or two, the catmint is easy to transplant.

I love being an animal! My horse loves eating wormy broccoli. Why wouldn't I love it too?

Do cabbage family crops really need to be grown without worms? As far as I can tell, the worms are perfectly edible. So what if a worm eats the leaves of a cabbage plant? They generally don't crawl inside the head. If I don't like worms inside cabbage heads, I can peel off a few leaves until I get further inside than the bugs are... Or I could find or breed a variety of cabbage with densely packed leaves that the worms can't crawl into as easily. These strategies also work with aphids. I can soak broccoli heads in slightly soapy water. Most of the worms fall off. And those that don't generally fall off in the cooking water.

I can catch the cabbage whites in a butterfly net to prevent them from laying eggs, or dust the plants with diatomacious earth. I can cultivate lots of predatory wasps to eat young caterpillars. There are both ground nesting and wood nesting predatory wasps. I can provide homes for both types. I can plant pollen producing plants to feed them.

...I solved the problem by planting Catmint near crucifers...

Nepeta cataria flowers are also good bee attractants late in the season (July-Nov.).
Hardy to zone 3.

Joseph Lofthouse wrote:
Do cabbage family crops really need to be grown without worms?

I generally encourage all kinds of caterpillars in my garden. Now that it's growing well, I have more than enough vegetables to eat and plenty to share with other critters. It gives the birds something to eat also.

@Joseph L.: "I can soak broccoli heads in slightly soapy water. Most of the worms fall off."

I'm working my way up to worms.....but haven't quite gotten there yet!

For cabbages, I'm thinking just some kind of Remay/Reemay covering might suffice because they seem to be somewhat of a "set it and forget it" crop, until it's time to harvest the heads. Don't know if Remay brings worse disease problems on account of the microclimate they provide, but it seems to help retard cabbage worms. We do end up using a bit of Bt if the infestation gets really bad on the kale, but for the most part just accept some predation by the worms. The typical post-harvest protocol during an infestation is to simply submerge the kale leaves in cold (well water) tap water for about 15 - 20 min. Seems this really makes the worms let go of the plant and they sink to the bottom of the basin. It's pretty rare for us to find a worm in the cooking after that.

I generally view Bacillus thuringiensis as a somewhat refined version of a compost tea. Since Bacillus thuringiensis is a naturally occurring soil bacteria, if you spray compost tea on your plants leaves then you are spraying them with Bt.

Joseph Lofthouse wrote:
I love being an animal! My horse loves eating wormy broccoli. Why wouldn't I love it too?

After last year's caterpillar invasion, we definitely had occasion to eat a few! Submerging plants in cold water does seem to work, but not on crinkly leaves, I learned. I found a lot of little green spiders in those crinkles, too, which didn't detach after a soak. Best to cook leaves with lots of other vegetables/meat in a nice dark sauce, and don't look too closely when eating

We had total defoliation on brassicas last year, starting late summer; some of the kale did not recover from such an attack, though they were probably not as strong as they could be, as we'd been harvesting all summer too. Probably 2/3 of the kale died from caterpillar damage. The Brussels sprouts managed to recover, maybe because they hadn't been harvested yet, though harvest was certainly delayed by a few months, after they regrew slowly in our cool autumn.

I know to watch for butterflies in July and September (we get two regular waves of them here), and my usual strategy is to inspect leaves and rub off eggs and newborn caterpillars, and pick off (and step on) larger caterpillars. I found this was not an easy strategy with either crinkly kale (too many hiding places) or Brussels (too many leaves!), my only brassicas last year. It's no problem to use this strategy on cabbage, as the butterflies only lay on the underside of leaves, and there are only about 4 or 5 leaves they can reach on a heading cabbage; not so on kale or Brussels. It was just too much to make an inspection of every single leaf on every single plant for weeks on end.

So I simply left the brassicas to defend themselves as much as possible and was thankful I still had chard so we weren't completely bereft of leafy greens. I did notice towards the end of the devastation many dead husks of caterpillars on brassicas, which had obviously been prey to parasitic wasps. Though there weren't enough to help me successfully defend my plants, I'm hopeful the wasp population will be much bigger this year because of so much easy prey last year.

As far as Bt is concerned; I don't even know if it's available here, but as I'm dirt poor, it's a non issue for me. I have to find other, free solutions.

I only grow smooth-leaved spinach. No point growing puckered-leaf spinach with all sorts of places for bugs to hide.

I'm with you, Joseph. Smooth leaved spinach only.

Without using bt, I can not get sellable broccoli. Sure, it's still edible, but a zillion tiny cabbage caterpillars can ruin the buds in a couple days. I've tried using water to spray the tiny caterpillars off, but it leaves so many behind still that the broccoli bud still gets ruined too much to sell. I've considered reymay "shower caps" for the broccoli, but our tradewinds get really brisk here. I'm not sure how much damage the cap would cause as it was whipped against the plant, twirled the way and that. Cloth row covers are impossible to keep in place for long during the trades.

Bt seems a decent solution for me. But because of my frequent evening showers, I need to lightly reapply almost daily. The same applies to my compost tea and any other foliar spray.

As far as I can see, bt is indeed a naturally occurring soil microbe. Buying a bag of bt doesn't seem all that different from making a bucket of aerated compost tea. The microbes are concentrated for spraying onto foliage. It is my understanding that the bt sold for caterpillar control only affects caterpillars because of the unique alkaline gut. It doesn't affect other "bugs".

I wouldn't mess with BT or anything that is toxic to butterflies or caterpillars.  Try to repel them naturally not harm them!

This year I learned from last year's mistakes (crinkly leaves, brassicas with lots of leaves), and only planted smooth leaf kale, spring sprouting broccoli, and winter cabbage.  For the first three weeks of the egg laying bonanza, I inspected leaves every evening for eggs and hatched caterpillars.  After that I ran out of steam and now only inspect plants superficially (i.e. a quick glance) every other day or so;  I pick off caterpillars and step on them.  There is not wanton destruction like last year, though if I had not been so diligent to begin with, I suspect it would have been.

Additionally, I have nasturtiums growing near my brassicas, and caterpillars are allowed free rein on them.  I like to think I'm selecting for nasturtium-preferring butterflies by rubbing off brassica-laid eggs but leaving nasturtium-laid.  I have heard they prefer them to brassicas (actually, I have not found this to be true in my experience), but if the caterpillars are born on them, they may possibly prefer to lay on nasturtiums when the time comes.  That's my story and I'm sticking to it