Dr Mike McCarthy is hoping for a perfect summer in South Australia’s Riverland this year. It will give him some important new data about the potential for evaporative cooling to help grapevines cope with heatwaves.
‘We had everything ready to go last year then the Riverland had such a cool January that the fruit in both of our trial sites had ripened and been harvested before the heat set in’, he said.
Dr McCarthy, a Principal Scientist with the South Australian Research & Development Institute (SARDI), is leading a three-year research project to investigate whether the use of micro-sprinkler irrigation can generate a more favourable mesoclimate (the climate of a particular vineyard site) that will counteract intense heat events. The evaporative cooling work is part of a larger project funded jointly by Wine Australia and the Department of Agriculture and Water Resources, through the ‘Filling the Research Gap’ programme.
‘What’s come out of the heatwaves we now seem to have been having for-ever-and-a-day is a working hypothesis that the damage during heatwaves appears to be because of hot nights’, he said.
‘We run workshops with growers in places like Mildura and they say to me “the vineyards seem to be able to cope with one hot day and a second day OK, but if we have two or three consecutive hot nights that’s when we’re starting to see the impact of heatwaves”.
‘The other thing they’re saying is that if they have a heatwave in January or early February the nights are short in terms of darkness and that doesn’t give the vines a chance to restore their turgor before the next day.’
And it’s not just about vine health. ‘We know from flavour chemistry that a lot of flavour compounds are pre-synthesised between fruit set and veraison, so again the hypothesis is that if we can cool the vines at night we can make sure synthesis continues and is not degraded during this critical period for varieties like Sauvignon Blanc, Chardonnay and even Cabernet.’
That is why the project has expanded to include trial sites in the Coonawarra – and Dr McCarthy admits to being surprised at how enthusiastically local growers came on board. ‘They said that if they get hot nights in February and March, their expression was that it “burns off Cabernet character”. And that means potentially very high value Cabernet fruit turns out not to be so good.’
In the Coonawarra, Treasury Wine Estates (TWE) viticulturist Allen Jenkins is co-ordinating the trials, comparing the impact of under-canopy sprinklers with large overhead sprinklers that can cool the whole canopy. They’re the ones used for frost protection at other times of the year.
In the Riverland, only under-canopy systems are being used and a series of sensors have been installed to keep track of temperature throughout the canopy when the micro-sprinklers are in operation. Dr McCarthy controls them from his home in the Barossa, making decisions based on information from the automatic weather stations near each site.
A comprehensive range of data is being collected and will be used to develop a heat transfer model to quantify the effectiveness of the approach under a range of conditions. Results are due later this year.
Dr McCarthy was one of the authors of the comprehensive factsheet on managing vineyards during heatwaves released by Wine Australia in 2014 (access it online here), and he’s very pleased with the response and the feedback from workshops around the country.
‘Growers are reacting positively – watching when heatwaves are coming and taking action’, he said. ‘The climate change message is getting through, but also we’ve been pushing the concept that if growers can better understand and manage extreme events they are going to be in a better position to go forward.
‘It’s about being proactive in terms of water, if that is their preferred option, or being proactive in terms of putting on some of these sunscreen sprays.’