FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY

In cases where the micro-element content of soil is very low, it is expensive to ‘fertilise the soil’ in an effort to obtain a satisfactory analysis and the philosophy should rather be to ensure that sufficient micro-elements are present in the immediate root environment of the vine. For Mn the recommendation is thus to apply 20 kg ha –1 Mn sulphate via the irrigation system or in solution on the berms of existing vineyards, and in the case of new plantings on the future vine rows just before planting holes are made. Manganese is relatively immobile in plants but deficiency symptoms in grapevines appear first on older leaves. The symptoms are light, general interveinal chlorosis, with areas around veins tending to remain green, with the result that the symptom, upon later expansion, strongly resembles a Mg deficiency. Manganese chlorosis is always a yellow colouration, even in red cultivars (Figure 18). Manga -toksi it ite is al by wingerd in die Breëriviervallei waargeneem o rooibruin, hoërliggende terrasgronde wat volop Fe-sulfiede (piriet) bevat, wat na swawelsuur oksideer, die grond versuur en hoë Mn-inhoude to gevolg het. Simptome is opgekrimpte, dik, opgerolde blare, met opgehewe speldekop-grootte, donker spikkels op lote, wat veral op die nodiums gekonsentreer is (Figuur 18). Trosse speen af en toon millerandage (bokhaelkorrels) . verkleuring, selfs by rooi kultivars (Figuur 17).

FIGURE 18: In contrast to Mg deficiencies, a Mn deficiency always display yellow chlorosis between veins, it is more speckled and does not occur as introversions (left). On older leaves the colouration is still yellow, even for red cultivars (right) (Photos: P.Raath (left); D. Saayman (right). Figuur 17: In teens elling met Mg-tekorte v rto n ‘n Mn-tek rt altyd geel chlor s tuss n n rwe, is dit mee gespikkeld en kom nie as instulpings voor nie (links). Op uer bl re is verkleuring steeds geel, selfs by roo kultivars (regs) (Foto’s: P.Raath (links); D. Saayman (regs)).

Manganese toxicities have been observed in grapevines in the Breede River Valley on red-brown higher lying terrace soils containing abundant Fe sulphides (pyrite), which oxidize to sulphuric acid, acidifying the soil and resulting in high Mn content. Symptoms are shrivelled, thick, curled up leaves with raised, pinhead sized, black spots on shoots, which are especially concentrated on the nodes (Figure 19). Bunches undergo berry shattering, with millerandage also occurring.

68 | MAINTENANCE FERTILISATION