Chemical Warfare in the Cabbage Patch

It’s mid August and the garden is awash in weeds. Some of the tomatoes are rotting on the vine; others are being devoured by slugs; none are ripening, save for a few cherry tomatoes that are splitting in the rain. Sun is needed for ripening. Rain promotes slugs and splitting. There has been no sun to speak of this summer; only rain. More than 21 inches since the beginning of June here in Temple, according to one of its residents.

But there is one crop – Brassica oleracea var. capitata ‘Ruby Perfection’ aka red cabbage that is thriving in the rain; it is even ready to harvest. According to Mark Hutton a vegetable specialist with Cooperative Extension at Highmoore Farm in Monmouth, because of all the rain this summer, cabbages suffered little if any damage from the cabbage worm, the offspring of the cabbage butterfly. Lots of rain meant there was little if any butterfly (Pieris rapae) activity surrounding the cabbages and their cousins. That meant there were few if any eggs laid on the underside of the leaves, few if any ravenous offspring to damage the plant and last but not least little if any messy dark green poop left behind. And any larva that did beat the odds were sure to be decimated by the fungal diseases spawned by the wet humid weather, says Hutton.

And as for the lack of sun? The cabbage is a leafy vegetable so there was no need to wait for the sun to turn it ripe red; it’s not a fruit like the tomato that needs to attract attention of herbivores in order to disperse its seeds. You harvest cabbage when it gets to the size you want. But don’t wait too long or it could split. According to FEDCO’s seed catalogue, the OG’s ‘Ruby Perfection’ is deemed mature in 85 days. Since the she planted her seedlings in mid-May, mid-August seems about right, especially given the fact right now the cabbages are the size of bowling balls and look like they could weigh about six pounds.

Long growing season
The OG confesses she is not one to start her cabbages from scratch; she lets the organic grower Jason Kafka of Parkman do the work for her. She purchased his seedlings in late April at the Fedco tree sale in Clinton. Kafka says that while there are a lot of varieties of green cabbages on the market, that’s not the case when it comes to red cabbage. And while there are varieties, such as ‘Red Express’

(65 days) that have shorter growing seasons than ‘Ruby Perfection,’ (85 days), Kafka says he prefers the longer season cabbage because its slow growth produces a more dense, energy-packed cabbage that makes for better storage. “Fast growing cabbages are like poplar trees; slow growing varieties like ‘Ruby Perfection’ are like oak trees,” says Kafka in describing their differences.

The OG prefers the slow growing red cabbage but more for its aesthetic than for its keeping and nutritional qualities (reported to be higher in vitamin C and fiber than green cabbage). While the folds of outer leaves of the cabbage’s compact head early in the season make for some slightly erotic photos in the vein of Georgia O’Keeffe’s flowers, it is the beauty of the pattern produced by the compacted leaves themselves when the cabbage is cut open that she marvel at.

Chemical warfare
But, as to be expected, the OG digresses. This column was to be about the chemical warfare waged by cabbages and other plants in the mustard family. According to the Cooperative Extension’s Mark Hutton, cabbages need not depend on flight-inhibiting wet weather to protect them from the cabbage white butterfly and its larval offspring.

It appears that they, like their cousins’ broccoli, rapeseed, cauliflower and mustard, have developed their own defense mechanism against their enemies. It’s a poisonous substance that is produced only when the plant is under attack by its leaf eating predators. At the heart of the defense is a class of chemicals in the leaf known as glycosinolates. They are the chemicals that are responsible for the tangy mustard taste of raw crunchy cabbage and the sulfur smell of overcooked cabbage.

According to a brief paper the OG found on the internet describing research recently done at the Max Planck Institute for Chemical Ecology in Jena, Germany, when a pest begins to feed on a cabbage leaf, it unwittingly releases an enzyme in the leaf that then interacts with the glucosinolates producing the poisonous chemical ally isothiocyanate aka mustard oil.

But what is to explain the fact that despite this chemical defense cabbages and their cousins are still plagued by extensive damage from their leaf eating predators. According to researchers at the Institute, it appears that some species of cabbage eating insects, including the cabbage white butterfly have developed an enzyme in their gut to either defuse the so called “mustard oil bomb” before it is activated or as in the case of the cabbage white butterfly cause the mustard oil bomb to produces a harmless chemical rather than a toxic one and blithely go on feeding. And to add insult to injury, these insects also appear utilize the glucosinolates and their by-products to locate suitable host plants to lay their eggs on. So much for chemical warfare in the OG cabbage patch!

Given the number of cabbage white butterflies that are attracted to her cabbages in a moderately rainy season, until the scientists at the Max Planck Institute can come up with a way to block the creation of the enzyme that defuses or sidetracks the “bomb,” the OG will continue to be ever vigilant in catching the butterflies before they lay their eggs and if she misses a few, will diligently stand guard and pluck their velvety green offspring from the cabbage leaves.

But for now, in this the beginning of the harvest season, she’s ready to cut open her first head of red cabbage and marvel at its beauty.

For those who want to get into the chemistry of the chemical warfare, google in the words “mustard oil bomb.” You’ll find many a scientific article on the subject.