1493_ Uncovering the New World Columbus Created - Charles C. Mann [133]
If Paris Green worked, why not market another arsenic-containing pigment, London Purple? Why not other chemicals for other agricultural problems? In the mid-1880s a French researcher discovered that the “Bordeaux mixture”—copper sulfate, used to keep children from eating fruit—would kill downy mildew on grapevines. Given a new chemical weapon, researchers pointed it at other pests and hoped it would prove as deadly as Paris Green. Quickly they found that copper sulfate was—oh, happy day!—the long-sought remedy for potato blight. Spraying potatoes with Paris Green, then copper sulfate, would eliminate both the beetle and the blight.
From the beginning, farmers knew that Paris Green and copper sulfate were toxic. Even before the discovery of its insecticidal properties, many people had got sick from living in homes with wallpaper printed with Paris Green. The thought of spraying food with this poison made farmers anxious. They dreaded the prospect of letting pesticides and fungicides build up in the soil. They worried about exposing themselves and their workers to dangerous chemicals. They were alarmed by the cost of all the technology. All of these fears came true, but all could be adjusted for, at least in part. For a long time, farmers didn’t know about the most worrisome issue of all: inevitably, the chemicals would stop working.
Colorado potato beetles are, genetically speaking, unusually diverse, which means that they have an unusually wide range of resources in their DNA. (In technical language, beetle populations have high heterozygosity.) Confronted with new circumstances, they adapt quickly. To farmers’ misfortune, these new circumstances included pesticides. As early as 1912 a few beetles showed signs of immunity to Paris Green. Farmers didn’t notice, though, because the pesticide industry kept coming up with new arsenic compounds that kept killing potato beetles. By the 1940s growers on Long Island found themselves having to use ever-greater quantities of the newest arsenic variant, calcium arsenate, to maintain their fields. Luckily for them, Swiss farmers spent the Second World War testing an entirely new type of pesticide on the potato beetle: DDT, a chemical bug killer with unprecedented range and sweep. Farmers bought DDT and exulted as insects vanished from their fields. The celebration lasted about seven years. The beetle adapted. Potato growers demanded new chemicals. The industry provided dieldrin. It lasted about three years. By the mid-1980s, each new pesticide in the eastern United States was good for about a season.
In what critics call the “toxic treadmill,” potato farmers now treat their crops a dozen or more times a season with an ever-changing cavalcade of deadly substances. Many writers have decried this, perhaps none more elegantly than Michael Pollan in The Botany of Desire. As Pollan observed, large-scale potato farmers now douse their land with so many fumigants, fungicides, herbicides, and insecticides that they create what are known, euphemistically, as “clean fields”—swept free of life, except for potato plants. (In addition, the crops are sprayed with artificial fertilizer, usually once a week during growing season.) If rain doesn’t fall for a few days, the powders and solutions can build up on the surface of the soil, creating a residue that resembles the aftermath