Brassica Attack

Cabbage Butterfly: the adult form of the Imported Cabbageworm (Corel Photo CD, 1993)

Remember how my nasturtiums were supposed to act as a sacrificial crop to protect the cabbage, broccoli, and cauliflower from cabbage white caterpillars? And how I wasn’t sure they’d be able to do the job because they couldn’t be planted until after the last frost, when the brassicas had already been in the ground for a month? Well, my suspicions have been confirmed. It was probably two weeks after I transplanted the brassicas into the garden that I saw the first little white butterflies dancing around my plants–gaily laying their eggs, it turns out. About ten days after that, I was wondering why the broccoli and cabbage leaves were filled with holes, some eaten down to the veins. But when I took a closer look, the answer was obvious: caterpillars. Inch-long suckers whose coloring blends perfectly with that of brassica leaves.

What to do? When I picked one of them up, it squirmed between my fingers, and I couldn’t bring myself to squash it. (Caterpillars have feelings, too! Well, maybe…) So I threw it several yards away, hoping that it wouldn’t find its way back. I did this with all the caterpillars I found that day, which was maybe seven or eight.

Well, I don’t know if they were the same caterpillars, but by the next day, there were almost the same number on the plants again. So this time I got brave. I threw the caterpillars onto the dirt and squished them with the toe of my shoe. They wouldn’t be coming back from that. And yet, more continued to appear every day or two. Finally, one day I was out in the garden barefoot, and I needed to squish some caterpillars. So I just took care of it in one rapid motion: pick caterpillar up, squish between the fingers, throw away. Very efficient. Though they leave behind a faint odor of garlic. Gardening, I’m learning, is an excellent remedy for squeamishness.

Well, I may have managed to save a few plants this way. But half of the broccoli, the green cabbage, and all of the cauliflower have succumbed, if not to the cabbage worms, then to something else. Maybe the abnormally high March temperatures were partly to blame. Or the withering April winds. Perhaps it’s my fault, for starting them in pots that were a little small (2 inches square) and crowding them at the window so they weren’t as strong as they could have been when I planted them out. Or for not watering them more once they were in the garden.

Sir Albert Howard, often called the father of the modern organic agriculture movement, believed that insects only inflict substantial damage on plants that are already weak, due to poor nutrition or unsuitable growing conditions. He would say that my cabbage worms were a symptom of inadequate gardening methods, that healthy plants aren’t bothered by pests. I’ve recently found this view affirmed by Eliot Coleman, in The New Organic Grower. He writes,

stress-initiated changes in the composition of plants…increase plant susceptibility to insects and diseases. The principle change is a stoppage in the synthesis of protein within stressed plants, which results in a buildup in the plant tissues of free (unattached) nitrogen. Since availability of nitrogenous foods normally limits pest numbers in nature, their populations can explode where stressed plants increase in easily available nitrogenous compounds. (176)

This makes sense to me, and I think I can see evidence of it in my garden. For instance, my first sowing of Tatsoi mustard grew slowly and had its leaves riddled with holes. My second sowing, however, sown when temperatures were a little more hospitable and watered more frequently, showed no such ill effects. It grew large and had no insect damage.

My one stunningly resistant broccoli plant!

Even looking at my broccoli, I see indications that Howard and Coleman are right. Out of the ten broccoli plants I set out in mid-March, I have one that is an absolutely gorgeous specimen with abundant large, deeply colored leaves. I have picked a total of one cabbage worm off of this plant, and that one didn’t seem to have eaten anything. Now maybe the cabbage white butterflies simply missed this plant when they were laying their eggs, and that’s the reason for its stunning success. But given that I did find one caterpillar on it, I don’t think that’s the story. It seems more likely that this plant was one of the few that got started in slightly larger containers. (Why didn’t I keep records on which those were?! I try so hard to write everything down, but some things inevitably slip through the cracks…) There are a couple of other broccoli plants also doing passably well, and maybe they also got better earlier treatment. In any case, the difference between this one broccoli plant and all the others is striking, and it makes me wish that next spring were already here, so I could pursue further experimentation.

As far as this year goes, I’m going to continue my caterpillar squishing, hoping to salvage a few of my struggling specimens. And I’m going to enjoy my red cabbages, which have not been affected at all. My guess is that their color is their best defense. No cabbage worm wants to crawl on a leaf where they’ll stand out like a neon sign to passing predators!