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Bordeaux mixture (also called Bordo Mix) is a mixture of copper(II) sulphate (CuSO4) and quicklime (CalciumOxide) used as a fungicide. It is used in vineyards, fruit-farms, vegetable-farms and gardens to prevent infestations of downy mildew, powdery mildew and other fungi. It is sprayed on plants as a preventive treatment; its mode of action is ineffective after a fungus has become established. It was invented in the Bordeaux wine of France in the late 19th century. If it is applied in large quantities annually for many years, the copper in the mixture eventually becomes a pollutant. As such its use is controlled, but not forbidden in most of the European Union. Despite this, some advocates of organic gardening consider it an 'organic' pesticide.
Because the copper ions build up in the soil, continuous use will cause heavy metal pollution. Copper also in organisms. It is thus restricted to use under control in 18 of the 27 European Union countries, with the exception of Cyprus, Greece, Bulgaria, Hungary, Italy, Malta, Portugal, Romania and Slovenia.
Thorough coverage of the spray on the plants is necessary. The Bordeaux spray continues to adhere well to the plant during rain, though in the long term it is washed off by rain. Commonly in practice, it is applied just once a year, in the wintertime. "Bordeaux Mixture" @ Integrated Pest Management @ UC Davis.
The conventional method of describing the mixture's composition is to give the weight of CuSO4, the weight of hydrated lime and the volume of water, in that order. The percentage of the weight of CuSO4 to the weight of water employed determines the concentration of the mixture. Thus a 1% Bordeaux mixture, which is typical, would have the formula 1:1:100, with the first "1" representing 1 kg CuSO4 (pentahydrated), the second representing 1 kg hydrated lime, and the 100 representing 100 litres (100 kg) water. As CuSO4 contains 25% copper, the copper content of a 1% Bordeaux mixture would be 0.25%. The quantity of lime used can be lower than that of the CuSO4. One kg of CuSO4 actually requires only 0.225 kg of chemically pure hydrated lime to precipitate all the copper. Good proprietary brands of hydrated lime are now freely available, but, as even these deteriorate on storage (by absorbing carbon dioxide from the air), a ratio of less than 2:1 is seldom used, which corresponds to a 1:0.5:100 mixture.
The chemical was in use as a blight preventive in the potato country of northern Maine by 1921. usda.gov Hurst, Lewis A. (1921) Soil Survey of the Aroostook Area, Maine, p.13 It started to be used by the United Fruit Company throughout Latin America around 1922. The mixture was nicknamed perico, or "parakeet", because it would turn workers completely blue. Many workers would get sick or die of copper poisoning.
After the downy mildew had struck, botany professor Pierre-Marie-Alexis Millardet of the University of Bordeaux studied the disease in vineyards of the Bordeaux wine. Millardet then noted that vines closest to the roads did not show mildew, while all other vines were affected. After inquiries, he found out those vines had been sprayed with a mixture of CuSO4 and lime to deter passersby from eating the grapes, since this treatment was both visible and bitter-tasting. This led Millardet to conduct trials with this treatment. The trials primarily took place in the vineyards of Château Dauzac, where he was assisted by Ernest David, Dauzac's technical director. Millardet published his findings in 1878, and recommended the mixture to combat downy mildew.
In France, the use of Bordeaux mixture has also been known as the Millardet-David treatment.
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