Bordeaux mixture

Bordeaux mixture (also called Bordo Mix) is a mixture of

Main uses

In addition to its use to control fungal infection on grape vines, the mixture is also widely used to control

Bordeaux mixture achieves its effect by means of the copper ions (Cu²⁺) of the mixture. These ions affect enzymes in the fungal spores in such a way as to prevent germination. This means Bordeaux mixture must be used preventively, before the fungal disease has struck.

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.^[3]

Preparation

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Bordeaux mixture can be prepared using differing proportions of the components. In preparing it, the CuSO₄ and the lime are dissolved separately in water and then mixed. Calcium oxide (burnt lime) and calcium hydroxide (slaked lime) give the same end result, since an excess of water is used in the preparation.

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.

Risks

Bordeaux mixture has been found to be harmful to fish, livestock and—due to potential buildup of copper in the soil—earthworms.^[1][2]

The chemical was in use as a blight preventive in the potato country of northern Maine by 1921.^[4] 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.^[5]

History

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In the 19th century, several outbreaks of

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 region. 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.

See also

• Burgundy mixture
• Phytopathology

Notes