Integrated strategies to manage seasonal variation in winegrape maturation

Abstract

The project aimed to develop strategies to minimise impaired or delayed fruit maturation. It investigated the effects of water deficits imposed through irrigation management on performance of own-rooted Cabernet Sauvignon vines. Linkages between treatment effects on vine physiology, carbohydrate status, yield components, berry development, fruit and wine composition were explored. Existing data sets from previous research and commercial sources were also analysed focusing on seasonal, regional and varietal effects on grape berry maturation. The study found that production may not been sustainable in the longer term with sustained deficit irrigation treatments, due to the reduced photosynthetic capacity and impacts on vine carbohydrate status. Management strategies to assist growers to improve the consistency of grape quality and meet set specifications were identified. These were (1) extended pre-veraison water deficits to enhance berry colour in seasons with low potential colour caused by high pre-veraison temperatures, applied with the caution that this treatment results in yield reductions and research on sustainability of this treatment beyond three seasons is yet to be conducted; (2) the application of particle film treatment (PFT) to reduce leaf temperature and minimise stresses associated with hot weather and/or water deficits.

Summary

The effect of water stress on the canopy results in smaller berries due to a lower water content while berry sugar concentrations are maintained similar to the non-stressed controls. Colour and phenolic concentration were not affected by deficit treatments but greatly affected by season.Yield was significantly reduced by both RDI (7%) and PD (15%) treatments compared to the control treatment over the three seasons. In the warmer season (2003), where berry colour was low, deficit treatments enhanced the quality of the wine (improved colour). It may be concluded that seasonal variation has greater effects on the physiology and the berry ripening process compared to deficit irrigation treatment.