I love cole crops. Brassicas.
Of course I’m not alone. Brassicas are considered the most important edible species out there. Broccoli, turnips, rutabagas, mustard greens, kale, cauliflower, brussels sprouts, cabbage. Yum.
And also of course, bugs love ’em, too. Lepidoptera, unfortunately. Pretty bugs. Moths and butterflies lay eggs on the leaves of brassicas, and the larvae which hatch then nosh on said leaves.
Those pretty white moths flitting over the garden? Cabbage moths. Responsible for the waxy, yellow patches on the underside of brassica leaves, then the stripey green larvae munching holes on those same leaves.
I try scraping off the eggs, hand-picking the larvae, but they always get ahead of me. I end up with this:
Enter Bt, or Bacillus thuringiensis. It comes in a concentrate, which is mixed with water and sprayed on the plants. It really works, too. Here you can see a cabbage with lower, bug-eaten leaves, and newer, pristine leaves.
What happened was I let things get ahead of me early in the season, then finally got on the ball and started spraying.
And here’s that same brussels sprout plant, with the tatty old leaves below the nice, whole leaves above:
So, yes, it works. But is there a cost?
As with everything, it seems, there is a downside. On a big scale, whenever you start to get successful at killing a bug, the bug changes to adapt to the challenge. Also, the other bugs, seeing an opening, start to take over. Plus, some lepidoptera which aren’t targeted for eating your cabbages might be affected. For example, if you planted parsley near your mustard greens and some overspray got on the parsley and a butterfly larvae ate it and died. (The downside here is provided that, like me, you like butterflies more than parsley).
Overall, though, Bt is a pretty decent solution to the problem of growing brassicas where pests are a big problem. Bt is considered safe for consumption by mammals, since it works by binding to a receptor which vertebrates (and all but a couple of invertebrates) do not have. Without that receptor, no harm is done.
Every time I hear something like that I reserve a small measure of disbelief. I’m a strong believer in the saying: If it seems too good to be true, it probably is.
So, with these caveats, it works in my garden. I try to use it sparingly, directly on what I intend it for, and far from the parsley and milkweed that the butterflies love.
As I move more and more into permaculture, I hope one day I won’t need to use Bt or any other pest ridder.
Have you had any experience with Bt? What do you do to protect your cole crops?