FERTILISER GUIDELINES FOR THE WINE INDUSTRY

Copper (Cu) The gap between sufficient Cu and a deficiency thereof in the plant, is very narrow and toxic concentrations is not much higher than those that are ‘nor mal’. Copper is normally assimilated by roots as the cupric ion, but also as certain chelates and uptake can also occur via the roots and bark. Copper has a profoundly essential role, as it is present in various proteins and is particularly found in oxidase systems, like i.a. cytochrome, polyphenol and ascorbic acid oxidase. In nature, copper is found in a large variety of minerals and in soil in the or ganic fraction, adsorbed to the soil colloids. Various soil factors can restrict the plant-availability of Cu, like the presence of lime (high pH), but also high AI-concentrations in highly weathered, leached and/or sandy soils. Copper deficiencies have been observed in the Strandveld region of the south coast in pastures and grain crops. Previously, however, attention has never been given to Cunutrition of grapevines due to the total absence of reports about defi ciencies, both locally and internationally. The apparent reason for this is the liberal use of Cucontaining fungicides. Recently Cudeficiencies have however been identified on the highlyweathered soils of the Cape south coast, as well as on

sandstone material against higher mountain slopes. Young plantings on Cu-poor soils are especially sensitive to Cudeficiencies and it appears as if cultivar differences also exist, with Pinot noir especially sensitive. Deficiency symptoms are not very specific, probably because poor root development is one of the effects of a Cudeficiency (typi cally only adventitious root development is observed on nodes and the bases of young vines). Consequently other nutrients are then also poorly assimilated and deficiency symptoms like those of Fe, Zn and K can be observed as a result. A copper deficiency causes stunted growth and a general irreg ular leaf yellowing, very comparable with that of simazine damage, which can develop into necrotic zones on older leaves. Further characteristics are shortened internodia which result in a witches’ broom appear ance, as well as dead growing tips (Fig. 24).

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