Bordeaux mixture (also called Bordo Mix) is a mixture of copper(II) sulphate (CuSO4) and quicklime (CaO) used as a fungicide. It is used in vineyards, fruit-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 region 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 sale and use is illegal in Great Britain and most of the European Union. Despite this, it has been promoted as an 'organic' pesticide. Main uses In addition to its use to control fungal infection on grape vines, the mixture is also widely used to control potato blight, peach leaf curl and apple scab. Although it may be bad for the environment, some organic agriculture advocates allow its use, so is often used by organic gardeners in some parts of the world. Because the copper ions build up in the soil, continuous use will cause heavy metal pollution. Copper also bioaccumulates in organisms. It is thus illegal to use in most European Union countries, with the exception of Belgium, Cyprus, France, Greece, Hungary, Italy, Malta, Portugal, Romania and Slovenia. Mode of action 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. Preparation 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.