Frost-fighting saves the day for vineyards

Stuart Dudley, regional viticulturist for Villa Maria, inspects grape vines after an overnight frost
Stuart Dudley, regional viticulturist for Villa Maria, inspects grape vines after an overnight frost

Frost protection at vineyards around Marlborough has thwarted any vine damage from a mild frost late on Tuesday night, viticulturists say.

Frost fans, helicopters and sprinklers were used throughout the region from about 11pm on Tuesday till 7am yesterday.

Wither Hills viticulturist Rex Butt said helicopters successfully warded off frost at the winemaker's Rarangi vineyard for about two hours from 4am.

"The temperature went down to zero around 3.30am - it went from 7.5 degrees Celsius to zero in three hours. It's the most dramatic drop in temperature we've seen for this season."

Fortunately, none of the crop was damaged.

A bad frost had been forecast, but it did not look like it was going to happen because of the cloud cover earlier that morning, Mr Butt said. "But around midnight, 1 o'clock in the morning, it cleared and the temperature just dropped like a stone."

Most viticulturists in Marlborough received two or three frost forecasts, but sometimes they never amounted to anything, he said. "You've just got to make a judgment call on whether it will actually happen."

The usual end date of the frost season was November 18-20, he said. "But you never know. I've heard of people having to deal with snowfall in December.

"A frost in November could significantly damage the crop - you could lose about 50 to 80 per cent of it . . . then the shoots get burnt off and you've lost two months of growth, so you have to start from scratch again."

That would result in a later harvest in May - the beginning of the frost season - which again meant an increase in the risk of crop damage, he said.

Villa Maria Estate regional viticulturist Stuart Dudley said there were no reports of damage to any of its crop thanks to the helicopters, frost fans and sprinklers used separately at each of its different vineyard sites.

TerraVin Wines co-owner Mike Eaton said wind machines and frost and diesel pots at its Omaka vineyard and water frost protection at its Awatere Valley vineyard had prevented damage.

Most vineyards in Marlborough had adequate frost protection in place and it was only in an "extraordinary frost event" that the risk of crop damage increased, he said.

"The only thing affected most is people, with a lack of sleep."

Marlborough Helicopters managing director Owen Dodson said its helicopters were operating for almost three hours from about 3.30am at vineyards on Middle and Old Renwick Rds and at Rarangi and the Southern Valleys.

Climate Consulting climatologist Stu Powell, who has been issuing frost warnings for Marlborough since 2005, said that cooler parts of Marlborough traditionally experienced a light November frost every second year, but the pattern varied around the region.

Yesterday's frost was the first to hit several of Marlborough's forecast areas since November 2006, he said.

Areas least likely to be frosted experienced strong drift winds at night, enough to keep air moving most of the time, which reduced frost risk, Mr Powell said.

Areas most likely to experience frost in Marlborough, from coldest to warmest, are: Wairau Valley township, Waihopai Valley, Fairhall, Southern Valleys, Ward, Seddon, Wairau Coast, Upper Awatere, and Rapaura.

Overnight lows on Tuesday:

Southern Valleys, -0.3C

Waihopai, -0.4C

Seddon, -0.1C

Fairhall, 0C

Wairau Valley, -0.6C

The Marlborough Express