Addressing fruit exposure and sunburn in Queensland wine grape vineyards

Abstract

While Queensland wine industry development has relied upon adoption of viticultural practices from established winegrowing regions, such procedures are not necessarily best practice under local conditions. The wine grape growing regions of Queensland are climatically distinct from other Australian regions with relatively wet growing seasons, and at times with severe peak heat loads. Queensland also hosts the most northerly and some of the highest altitude vineyards in Australia, with higher ultra violet radiation exposure than any other Australian grape growing region. Furthermore, fruit exposure may be exacerbated by regional management practices (e.g. leaf plucking, shoot thinning) used to minimise risk of fungal infection (e.g. botrytis, bunch rots). The Queensland wine industry had identified fruit exposure management as a critical issue to be addressed. We set up demonstration sites to show the impacts of canopy management options on exposure of Chardonnay and Shiraz over the 2009/10 vintage in the Granite Belt, South Burnett and Scenic Rim. Demonstrated options included sprawl, VSP, fruit zone leaf removal at pea size and véraison (easterly or both sides of canopy), bird netting, or commercial sunscreen products (calcium carbonate or kaolin clay). Differences in fruit exposure, grape and wine quality were noted. Growers inspected the demonstration sites prior to harvest and provided feedback on fruit quality. Fruit was harvested, analysed and wines made and analysed, and results presented and discussed at the 2010 Queensland Viticulture Seminar. At this seminar / workshop, industry participants were also able to conduct sensory evaluation of the wines to determine any impacts of alternative management practices on wines produced, to supplement their evaluation of fruit quality prior to harvest. Conclusions from this project were confounded by problematic seasonal conditions with diverse severe events including frost, hail, heat and water stress and fungal disease pressures. Recommendations from this study are that while they may be useful in cooler seasons, in hotter seasons practices such as leaf plucking and shoot thinning are not advised due to potential to exacerbate overexposure and sunburn of fruit.