Friday, September 24, 2010

Plan for the Cabbage Worms

According to the Bug Review pages of University of Illinois's Extension office, there are actually three kinds of cabbageworms in Illinois. It seems likely that the same three pests are present in Georgia, too. And the result of all of them, if their preferred crop is left completely undefended, is the same: severe damage, to the point of "complete defoliation." Anyone who has seen this, along with the slimy-looking green feces left behind by the voracious caterpillars, knows that this is not a pretty sight.

Even though the name seems to limit these critters to cabbages, it really refers to the whole family of plants that cabbages are a part of, the Brassicaceae. At least one of the three kinds of caterpillars comes after my cabbage-family plants every year.

Usually, I cover my Brassicas with tulle or some other row-cover, to keep the parents of these caterpillars, mostly white butterflies, from laying eggs on the plants. No eggs means no caterpillars, so this plan works pretty well. However, the netting, propped up over the plants, in various configurations around the front yard, isn't exactly attractive.

Since the usual organic recommendation for caterpillar control is Bt, I decided to try it this year, hoping to avoid using so much netting in the front yard. As soon as the cabbage family plants were visible above ground, for those direct-seeded, or transplanted out to the yard, I started the weekly spraying. The brand of Bt I was able to find is Thuricide, and so far, it seems to be working.

The one drawback is that the caterpillars have to actually hatch out of the eggs and eat a little of the Bt for it to work. That means that a lot of the leaves of my brassicas have little holes in them. For the broccoli, this is not a problem at all; I'm not planning to eat the leaves, and the holes are pretty small:

Thinking about what this means for the flower buds of the broccoli plants that I want to eat, though, gives me pause. I know I am spoiled by the flawless heads of broccoli at the store, but I am hoping for some fairly pristine broccoli.

The bok choy is showing a little more damage than the broccoli. Maybe it is tastier?

I had kind of been hoping for leaves with fewer holes, so I may, as the plants get larger, cover the bok choy with netting. I know this sounds like overkill, but again, I would like to have a crop that is as beautiful as it can be, within reason.

When I decided to try the Bt, I obviously hadn't thought it through completely. It makes perfect sense that the caterpillars are going to have to eat a little bit of leaf in order to get enough Bt into their systems to kill them.

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