FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY

CHAPTER 5

FIGURE 21: Zn deficiencies also lead to berry shattering, straggly bunches and berries with few or no pips (Photo: D. Saayman).

TABLE 24: Norms for the Zn contents (mg kg –1 ) of leaf blades and petioles of grapevines.

Fruit set

Veraison

Leaf blades

Petioles

Leaf blades

Petioles

Minimum Sufficient

Minimum High Minimum High Minimum High

15

30

15

100

15

30

15

50

Zinc oxide, zinc sulphate and organic Zn-chelates are marketed as foliar nutrition. The last mentioned is completely soluble in water and should theoretically 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% solution of spray-lime (slaked lime, Ca(OH) 2 ) and sprayed at a concentration of 0.4%. Efficacy of uptake is increased by mixing the zinc containing 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 commence before flowering already, where deficiencies occur. A second application can be made later in the season, at pea berry stage.

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