Saturday, April 11, 2009

Cabbage Aphids (Brevicoryne brassicae)

It started so innocently. One day I noticed a few aphids on the tip of a flowering stalk on one of my collard plants. I cut that tip off, but noticed another tip with aphids on them. I thought to myself, "Here's an opportunity to observe nature in action. Predator versus prey. Can the plant protect itself? Will parasitic wasps and ladybugs and lacewings move in and lay waste to this enemy?"

The parasitic wasps and ladybugs did move in and make a valiant effort, but not before the population of aphids exploded on my patch of collards. Aphids are literally born pregnant, but that is not the end of the chain. The fetus inside is also pregnant! So each aphid bumbling and slurping up the precious phloem in the plant is pregnant with her own granddaughter!

Aphids that prey on Brassica oleracea (broccoli, cauliflower, kale, collards, cabbage, brussels sprouts, kohlrabi, and kin) can convert the plant's own defense chemical, glucosinolate, into a kind of mustard oil that can deter some predators, such as larval two-spotted ladybugs.

Aphids in the garden patch in spring are a sign of a cool spring, because some of the predators, like lacewing larvae, will not hatch out until the temperatures are consistently warmer. As the weather warms up going into summer, the aphids die back anyway because the symbiotic bacteria that help them digest their sappy meals cannot tolerate higher temperatures.

Yesterday I pulled out any remaining straggly collard plants. I had already harvested seeds about a month ago from the plants that bolted before the aphid attack. Since we started focusing on buying a house with my parents a few months ago, I ceased to plant new garden beds. I still have my Indian onions growing and some cucumber young plants that got planted before we really decided to make the move. The onions will get moved and I will ask our rentors if they want to keep the cucumbers. The collard bed is a sunken bed, just like the others--I realized that it is one of the best ways to garden in the desert. The earth in the collard bed is dark and soft, so beautiful; I am sad to leave it. Erik wants me to top off the depression, which means covering it with the sandy gravely compacted dirt that I had so laboriously removed when pregnant with Micah. Once covered up, that lovely loamy earth underneath will be like prime real estate for all the weeds that roam this area-- Bermuda grass, wild mustard, cheeseweed, spiderling.

And yet, there are always more seeds, more opportunities, waiting to be planted and nurtured, tended to and cared for. Why lament the end of a garden plot? Because then it really meant something. It had a purpose; it fed us and taught us and showed us stuff about life and the universe. And then it got attacked. And then I finished its life. Yes, I, killed my garden. The aphids and I; I and the aphids.

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