One of the most ubiquitous pests we deal with on our fall crops is the appropriately named Cabbage Moth and it’s offspring the Cabbage Looper (so called due to it’s inchworm-esque mode of walking). In addition to its namesake, the Cabbage Looper also is quite fond of most other cole crops including broccoli, cauliflower, and kale. Or put in another way: roughly half the crops we grow in the fall, by acreage.
Unlike some other pests, Cabbage Moths are not sneaky or hard to detect. On warm, sunny afternoons, the little white moths can be seen from five hundred feet away swooping their way across our fields, stopping for a brief second here and there to alight on a leaf and lay some eggs. A week or so later, the eggs hatch and the tiny green worms begin to ferociously munch on the crop leaves, doubling in size every day. If left unchecked for two or three weeks, they can destroy a head of cabbage or render most of the leaves on a kale plant unmarketable. There is rarely only one worm on a plant.
Luckily, the caterpillars are fairly easy to control using the natural and organic bioinsecticide Bacillus Thuringensis (aka Bt), a bacteria that sickens them and stops their feeding. It biodegrades in less than two days. We generally spray it on our cole crops every two weeks while they are small; once the plants are a month old the insect damage is much less impactful. Following this program, we keep moth populations fairly low.
For the last three years, though, our neighbor right across the road from us has been growing alfalfa — another favorite food of the Cabbage Loopers. When alfalfa prices are high, farmers spray the crop to control the pest. But lately alfalfa prices have been so low that they cannot justify the cost. All summer long, the neighbor’s alfalfa field was alive with swooping, diving yellow moths (the moth’s wings turn yellow due to the high beta carotene content of the alfalfa). And every time the field is cut for hay, the moths flood across the road onto our farm in search of good places to lay their eggs.
With such a large population fighting for egg-laying spots, the moths appear to become less selective. One day while I was checking our kale field for worms, I noticed the leeks planted in the next field over looked strangely deformed. Upon closer inspection, I found the tiny green caterpillars were chewing on the leek leaves, causing them to wilt or curl up in response. We had never had to spray leeks for caterpillars before, and it turned out they are much harder to control than they are in cole crops, as they hide in the tight crevices between the narrow leaves.
Luckily, leek leaves are not the edible part of the plant, but the worm damage stunted the plants growth and caused cosmetic damage. We normally start harvesting leeks in mid-October, but this year we have just begun picking them and they are still a little on the small side.
The cooler, wetter weather we’ve had so far in December has ended the Cabbage Moth season and is helping the leeks recover from their assault. As we go into winter, you’ll start seeing leeks in your boxes fairly frequently as you do most years.
It always makes me happy when subscribers tell me that Terra Firma’s CSA has expanded the culinary horizons of their families. I can’t say I’m quite as excited to have the same effect on the insects.