June 2010. Scalded by the Steam: Being a discourse on killing weed seeds and nematodes using solar heat.

“They found him in the wreck with his hand on the throttle, and scalded to death by the steam.”

Our topic for the month actually has nothing to do with the Wreck of Old 97 and the ballad it inspired from which that lyric is drawn. But those of you who have been with us for a while will recognize that this is a new and improved version of an article we wrote eight years ago. Gardening has become more popular since then and we have thought a bit more about the method for killing weeds, weed seeds, and nematodes with moist heat—using the summer sun as the heat source. The system works but could be improved with a little more innovation.

Leon: The process we described is now called solarization. It originated back in the early seventies when an Israeli research man was fumigating the soil with a poison gas called methyl bromide. At least he thought he was. He dug a shallow trench around the plot, spread a clear plastic sheet over the area, buried the edges in the trench—and forgot to release the gas under the plastic. A week later he removed the plastic and found that the treatment had killed weeds and seeds as well as it would have if he used the methyl bromide. The key was that the hot desert sun heated the soil much like our sun will heat a car if you forget to lower the windows.

He published a paper on this at the time, when I was trying to find non-chemical methods for weed control in home vegetable gardens. The problem was not so much that the herbicides were too toxic for use with vegetables, but rather that most chemical companies didn’t want to label their herbicides for that sort of use. The risk of lawsuits was too great for the small quantities of product that would be sold. At a science meeting I met a like-minded man from California, so we divided up the efforts. My assignment was to study what happened to the weed seeds and nematodes. The California man, with much better facilities and more money, focused on techniques and the fate of soil organic matter under the high temperatures. It turned out that the solarization treatment worked much better in California than it did in Louisiana. The difference was that California gardeners could expect two weeks in July or August with full sun and no rain. In Louisiana we could hope for that but it wouldn’t happen.

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