FERTILISER GUIDELINES FOR THE WINE INDUSTRY

Zinc oxide, zinc sulphate and organic Znchelates are marketed as foliar nutrition. The last mentioned is completely soluble in water and should the oretically be more effective. Zinc oxide can be sprayed as a 0.2%solution, but Zn-sulphate scorches easily and is mixed with a 0.3% spray-lime (slaked lime, Ca (OH) 2 ) and sprayed at a concentration of 0.4%. Efficacy of uptake is increased by mixing the zinccontaining substance with urea (0.5%solution). If fungicides containing Zn are used, sufficient Zn is normally provided to control latent deficiencies, but it is not sufficient to rectify visible deficiencies. As Zn plays a role in fruit set, foliar nutrition should already be commenced before flowering where deficiencies occur. A second application can be made later in the season during pea berry stage. In general Zndeficiencies are difficult to correct with foliar sprays and a more effective treatment has proven to be the painting of spur pruned wounds with a strong Zn-sulphate solution (10%) within 3-4 hours after pruning, before strong sap flow commences. Spraying of pruned vines a few weeks before bud break with 4%-Zn-sulphate or ZnO (together with 1.3% lime sulphur), is recommended.

FIGURE 24: Irregular yellowing (left), comparable to simazine damage (centre), necrotic zones and dead growing tips (right) due to Cudeficiency.

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