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-based 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 under less severe water deficit in two out of three years when particle film was applied to the vine canopy. Particle film influenced the rate of stomatal conductance at leaf temperatures between 22 and 33°C under the most severe water deficit and response differed by cultivar, suggesting that stomatal control 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 we observed between cultivars in response to the particle film limit the applicability of our results to cultivars with similar response to drought as Cabernet Sauvingnon and Malbec.