FERTILISER GUIDELINES FOR THE WINE INDUSTRY

The Cu-content of soils is also determined through EDTA-extraction, and for soils with a pH KCl of between 5.0 and 6.5, the Cu-content should be at least 0.5 mg kg -1 (see Table 5 in Chapter 3). In cases where supplementation is required, soil application of Cu-sulphate at 15 kg ha 1 can be made, like for Mn or Zn, or combined therewith. The norms for Cu-contents of leaves are indicated in Table 17. A level of 6 mg kg -1 Cu in leaf blades during pea berry stage can serve as general guideline for sufficient Cunutrition. TABLE 17: Norms for the Cu-contents (mg kg -1 ) of leaf blades and petioles of grapevines. Fruit set Leaf blade Petiole Deficiency Sufficient High Toxic Deficiency Sufficient High Toxic <3 >6 NA NA <3 5-10 25-50 >50 Veraison Leaf blade Petiole Deficiency Sufficient High Toxic Deficiency Sufficient High Toxic <3 >6 NA NA <3 >5-15 25-50 >50 NA – not available. There is concern that the continual use of Cu-containing fungicides can lead to Cu-toxicities, as is indeed the case in certain parts of Europe. Locally it was found by Conradie that for nurseries, where the most of these sprayings probably occur, the Cu-contents of the soils are not excessively high and that Cu-contents of up to 50 mg.kg -1 still did not have meaningful negative effects. Copper is fixed at soil pHs (KCl) of > 4.3, hence toxicities are first expected on acidic, lightly textured soils, with liming of soil to an optimum pH of 5.5 being the apparent solution.

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