Bordeaux mixture

It is sprayed on plants as a preventive treatment; its mode of action is ineffective after a fungus has become established.

If it is applied in large quantities annually for many years, the copper in the mixture eventually becomes a pollutant.

[3] Because the copper ions build up in the soil, continuous use will cause heavy metal pollution.

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.

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.

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

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.

Millardet published his findings in 1878, and recommended the mixture to combat downy mildew.