copper, a micronutrient required in very small concentrations for healthy vine growth. Copper is toxic to plants except in very dilute concentrations. Reports of copper deficiencies in vineyards are rare, probably because of the very small requirements by the vines, but also because of the widespread use of fungicides containing copper. In acid soils, the copper from fungicide sprays can actually reach toxic levels and some parts of the médoc have been affected by copper toxicity. After the annual application of several kg of copper per ha, as in bordeaux mixture, for about a century, the level of copper in the soil can be toxic and the vine growth became severely stunted. Generous applications of organic matter make the copper make less available to the vines. Additions of lime will help to neutralize the toxic effect of copper by raising the soil pH. See also casse.
