Kaolin Particle Film and Water Deficit Influence Red Winegrape Color under High Solar Radiation in an Arid Climate

The main and interactive effects of a kaolin particle film and water deficit on vine and berry attributes of winegrape cultivars Cabernet Sauvignon and Malbec were evaluated over three growing seasons in the warm, semi-arid climate of southwestern Idaho. Berry concentrations of total anthocyanins increased with increasing severity of water deficit in both cultivars in all three study years; however, the increase was accompanied by a decrease in berry fresh weight. An equal or greater increase in total anthocyanin concentration with greater berry fresh weight was achieved in two out of three years under less severe water deficit when particle film was applied to the vine canopy. Particle film influenced stomatal conductance and leaf temperature and response differed by vine water status and cultivar, suggesting that drought response influenced the effectiveness of the film. Under the climatic conditions of this study, the combination of particle film and mild water deficit provided the greatest net increase in anthocyanin concentration. The differences observed between cultivars in response to the particle film limit the applicability of our results to cultivars with similar response to drought as Cabernet Sauvignon and Malbec.