• Charles Sturt research in Orange vineyards has identified the best time to remove leaves from vines to reduce sunburn damage
• Sunburn can lead to downgrading of fruit causing significant economic losses to growers and wineries.
• The study of Chardonnay grapes showed early leaf removal led to a higher accumulation of photo-protective compounds in the grapes

Research by the National Wine and Grape Industry Centre (NWGIC) is shining new light on how to reduce sunburn damage on grapes by identifying the best time to remove leaves from the vine.

In a Wine Australia funded project, Charles Sturt University (Charles Sturt) postdoctoral researcher Dr Joanna Gambetta (pictured) investigated the impact of the timing of defoliation on Chardonnay grapes in two vineyards in Orange.

She found early leaf removal led to a higher accumulation of photo-protective compounds in the grapes earlier in the season allowing them adjust to hotter conditions and reducing the incidence of sunburn.

“Sunburn can affect up to 15 per cent of winegrape berries in Australia in any given season as a result of high-light in combination with high ambient temperatures and ultraviolet (UV) radiation,” Dr Gambetta said.

“This can lead to downgraded fruit causing significant economic losses to growers and wineries.

“We studied three different timings of defoliation of Chardonnay berries: a control group where leaves were 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 were removed at véraison (mid-January), when the sun was at its fiercest and the grapes at their most vulnerable.”

The study's key findings were:

• Leaf removal led to higher final concentrations of all photoprotective compounds when compared to the non-defoliated control.
• Marked differences were observed in the accumulation patterns of the photoprotective compounds between berries defoliated early (end of flowering) and those defoliated later (véraison).
• Amongst all three treatments, sunburn damage was higher in grapes on vines defoliated at véraison.
• There were no significant differences between yield, total soluble sugars, pH, titratable acidity and YAN between treatments within each vineyard.

The focus of this research through Wine Australia’s Incubator Initiative was developed from the priorities identified by Wine Australia’s Regional Program partners in NSW to support growers in finding locally tested solutions to industry problems.

Dr Gambetta will present the findings of her research at the NSW Department of Primary Industries (DPI) Spring Vine Health Field Day at the Orange Agricultural Institute on Thursday 26 September.

The NWGIC is an alliance between Charles Sturt, the NSW DPI and the NSW Wine Industry Association.