Here on the Ducru-Beaucaillou estate within the Bordeaux region of France, nearly a hundred and fifty years ago, the vineyard manager Ernest David, sprayed a solution of copper sulfate and lime on his ripening grape vines to impart a blue-grey mottling to them, thereby dissuading passers-by from “sampling” them.  Serendipitiously, this concoction applied to give vines a sickly look,  to  prevent local pilferage actually  was the first effective fungicide.  This blue-grey mottling was noticed by the French botanist and Professor of Botany at Bordeaux University, Pierre Marie Alexis Millardet. Millardet noticed that the vines with the odd coloration were healthy, leafy, and vigourous while those without the blue-grey coloration on neighboring estates were sickly in appearance, losing leaves, and obviously infected with an unknown agent.  The causitive agent, an oomycete, known as Plasmopara viticola or Downy Mildew, which was unknown at the time, was under study by Millardet and later discovered by him and his coworkers.  After speaking with vineyard manager Ernest David and learning of the copper sulfate, lime and water concoction, its intended purpose and the unexpected results, Millardet went to work.  In subsequent years of testing on infected grape vines,  Millardet proved that the lime and copper sulfate solution was an effective means of control for the mildew of grapes.  The "Bordeaux mixture" as it is now known, was also instrumental in control of other oomycete crop diseases, such as the infamous Phytophora infestans or late blight of potato responsible for the Irish Potato Famines of the 1900's. 

--T.M. Jones 2008