Sunburn is hurting fruit

By Country News

High temperatures, harsh light and UV radiation can lead to a nasty case of sunburn, not just for people but for wine grapes, and Charles Sturt University is investigating how to reduce the damage and financial losses.

The project by university post-doctoral researcher Dr Joanna Gambetta, from the National Wine and Grape Industry Centre, has been funded by Wine Australia’s Incubator Initiative.

‘‘Sunburn can affect up to 15 per cent of wine grape berries in Australia in any given season,’’ Dr Gambetta said.

‘‘The browning, cracking and berry shrivelling means that yields are reduced and the fruit can be downgraded, causing significant economic losses to growers and wineries.

‘‘On a sensitive, fully mature chardonnay grape, symptoms of sunburn can appear within five minutes once surface temperature on the berry reaches an ambient temperature of 40 to 43°C.’’

Dr Gambetta said sunburn of grape berries was influenced by a number of factors, including grape variety, the stage of development, water stress and canopy management.

‘‘Grape growers can remove leaves from the vine to aid in disease management and my research aims to identify the optimum time for leaf removal to balance disease reduction and sunburn, as well as determining how altitude affects the degree of sunburn,’’ Dr Gambetta said.

Experiments in vineyards in Orange, NSW, are examining three different timings of defoliation of chardonnay berries: a control group where leaves are not removed at all; a second group where leaves were removed at the end of flowering in December; and a third group of vines where the leaves will be removed at véraison (mid-January), when the sun will be at its fiercest and the grapes at their most vulnerable.