Abstract
Transpiration rates of Shiraz vines grown on a two wire vertical trellis were measured using sap-fow sensors and used as a basis for applying different levels of post-véraison irrigation. The effect of this differential irrigation on plant water status and grape composition were investigated with responses of vines on the upper and lower wires of the trellis studied separately. The concentration of juice total soluble solids and pH was unaffected by irrigation treatment but the concentration of berry anthocyanins and phenolics, expressed as mg/g berry mass and absorbance units/g berry mass respectively, decreased with increase in water application, mainly due to an increase in berry weight. Predawn leaf water potential was measured from veraison to harvest and the water stress integral (S<sub>ψ</sub>) was calculated as an indication of the intensity and duration of water stress in the three irrigation treatments. S<sub>ψ</sub> was found to be closely correlated with post-veraison water use and with grape composition.
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