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Night watering helps vines keep their cool in heatwaves

Primary Industries

Irrigating vineyards at night during heatwaves can reduce fruit losses by 30 per cent, a scientific study has shown.

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The project has run at a vineyard in the Riverland, Australia’s largest wine grape growing region, the past two Australian summers.

It is scientifically proving the most effective and efficient methods of protecting grapes from heat damage such as leaf scorch, reduction in grape quality and lower yields.

Vignerons have long suspected that hot nights were as much to blame for heat damage as hot days, particularly after three or four consecutive days of scorching heat.

Principal Scientist with the South Australian Research Development Institute Mike McCarthy is leading the project, which is funded by Wine Australia via the University of Adelaide.

The original project began in 2014 and installed under-canopy sprinkler systems at sites in the Riverland and Coonawarra to provide an evaporative cooling effect for the vines.

The results were surprising.

Even though the under-canopy sprinkler system delivered very little evaporative cooling of the vines, the nighttime irrigation increased yields – or effectively reduced losses – by a minimum of 30 per cent. This led Dr McCarthy to begin the second study in 2016 using traditional drip irrigation systems to water at night during hot conditions

“It wasn’t the cooling effect of the air so much but more so the cooling of the ground and the root system and rehydrating the root system in preparation for the next day,” Dr McCarthy said.

“The last two years the focus has been if we put the same amount of water on through the drip system at night as we were through the under canopy sprinklers, do we get the same effect?

“Based on last year’s data we are achieving the same effect just by turning the drip irrigation system on at night rather than turning the canopy sprinklers on.”

This year’s grapes will be picked this month and Dr McCarthy expects the results to be similar to the 2017 vintage or potentially better because of the increased number of heatwave events in South Australia this summer.

He said the vines did not require more water it was just the timing of when the irrigation was applied that was critical.

“The other week the Riverland was having days of 45 degrees (Celsius) and that’s in the shade so what’s the temperature on the bare unprotected soil during the day – pretty damn hot,” Dr McCarthy said.

“What this night-time irrigation is doing is cooling that soil down at night, which is of benefit to the root system, and the roots are also being rehydrated at night for the next day.

“We’ve been finding that at midday the next day the canopy temperatures were up to five degrees cooler than the control vineyard so that little bit of water at night was still having a significant positive effect on vine physiology in the heat of the day the next day.”

Wines made from grapes grown in the test vineyard have been put through sensory evaluation and compared against wine produced from the nearby control vineyard.

Dr McCarthy said there was no diminution of flavour or decline in quality attributes as a result of the 30 per cent higher crop.

“So growers don’t need to worry that this night watering is going to have an effect on quality – maybe it is even having a positive quality effect on some attributes,” he said.

“The biggest problem most growers have got is their irrigation system hasn’t got the flexibility to water all of their blocks in the one night.

“Maybe now there’s some good hard science behind it growers will be prepared to invest some more money in upgrading their irrigation systems.”

Barossa Valley vigneron Will Holmes has about 65ha of vineyards in Gomersal where he grows Shiraz, Cabernet, Grenache and Tempranillo.

He has invested $200,000 on extra storage tanks and extra pumping capability in recent years so he can irrigate his vineyards by pulsing it through the night.

“I’ve basically put a drought management and a heatwave policy in place based on exactly what Mike McCarthy has recommended on a commercial scale,” Holmes said.

“It works 100 per cent but you’ve got to be set up to be able to achieve it. You’ve got to have a big enough irrigation system and the ability to put out a lot of water very quickly.

“We had one year when we estimated we were losing $20,000 a day in a heatwave and you just don’t get those losses with this system so it pays for itself very quickly in a hot year.”

Holmes said a number of vignerons had come to look at his system with a view to replicating it.

He said he knew of “plenty” of Barossa growers who had taken hits during the recent heatwaves.

“What their losses are I don’t know but I would estimate they will have lost 20 to 30 per cent of their fruit and they’ve lost canopy, which is very important for ripening over the next month,” Holmes said.

Dr McCarthy’s final report, including the results from the 2018 harvest, will be lodged with Wine Australia by June 30.

South Australia is consistently responsible for about 50 per cent of Australia’s annual production and includes 18 regions such as the Barossa Valley, McLaren Vale, Adelaide Hills, Clare Valley and Coonawarra.

This is a Creative Commons story from The Lead South Australia, a news service providing stories about innovation in South Australia. Please feel free to use the story in any form of media. The story sources are linked in with the copy and all contacts are willing to talk further about the story.

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