French winemakers have lit thousands of small fires to ward off frost which is set to badly hit this year's production, according to industry experts.

The vineyard fires have caused a layer of smog in the southeast of the country, local authorities reported Thursday.

The practice of lighting fires or candles near vines or fruit trees to prevent the formation of frost is a long-standing technique used in early spring when the first green shoots are vulnerable to the cold.

Protecting the vines from sub-zero temperatures
Protecting the vines from sub-zero temperatures AFP / JEFF PACHOUD

Whole hillsides look as if they are ablaze, creating a striking visual effect, with winemakers scrambling this week as temperatures plunged to below freezing, particularly in the fertile Rhone valley in southeast France.

The frost which has hit a large proportion of French vineyards in recent days is "one of the most serious in recent decades" and will cut production of the year, the CNIV national winemakers' association warned.

"We already know that we will have a very low harvest in 2021," said Jean-Marie Barillere, head of the Comite Europeen des Entreprises Vins (CEEV), a European wine trade group.

French winemaker Remy Nodin looks at his vine buds damaged by the frost the night before in Saint-Peray, near Valence, on April 8, 2021
French winemaker Remy Nodin looks at his vine buds damaged by the frost the night before in Saint-Peray, near Valence, on April 8, 2021 AFP / PHILIPPE DESMAZES

The frost has "affected 80 percent of French vineyards", he said. "Arborists and wine growers have just suffered a dark week."

Barillere said it would take around ten days for the profession to accurately assess the state of their grapevines and estimate the damage.

This picture taken on April 8, 2021, shows an apricot orchard after a night of frost in Veaunes, near Valence, Southeastern France
This picture taken on April 8, 2021, shows an apricot orchard after a night of frost in Veaunes, near Valence, Southeastern France AFP / PHILIPPE DESMAZES

Regional air quality monitoring body Atmo Auvergne-Rhone-Alpes issued a warning about the fire-induced fine-particle pollution in the southeast region which includes the city of Lyon where a layer of smog was visible on Thursday.

"It happens almost every year when there is a frost, but this time it's massive," director Marie-Blanche Personnaz told AFP of the pollution.

She said farmers were "entirely within their rights" to light fires to save their livelihoods, "but we perhaps need to work on the problem and find other solutions when the (frost) phenomenon is significant."

In an attempt to combat the frost which has followed a couple of weeks of mild weather, growers have installed candles between the 1,700 apricot trees on this farm in Saint-Prim, Isère. The fruit tree, which flowers early, is very sensitive to frost.
In an attempt to combat the frost which has followed a couple of weeks of mild weather, growers have installed candles between the 1,700 apricot trees on this farm in Saint-Prim, Isère. The fruit tree, which flowers early, is very sensitive to frost. AFPTV / Hassan AYADI

Some winegrowers use wind machines to keep frost from setting in.

Others use water sprinklers, allowing a fine coating htting sub-zero temperatures as the ice acts like a mini-igloo.

This year's two-night cold snap could be particularly damaging for winemakers and other fruit farmers because the freezing temperatures came after a week of unseasonably warm weather.

Christophe Gratadour, an industry specialist, said that the central Loire area and the Rhone region had been affected.

"All sectors have been hit but it's still too early to measure the effects," he told AFP.

In the wine heartland around Bordeaux, producers' body CIVB warned that it was "certain the spring frost will severely affect the harvesting volumes in 2021."

Winegrowers and farmers told AFP of their desperation as they inspected the damage on Thursday morning after a second night of trying to keep the ice at bay.

"We worked on the main hillside and burned straw bales and piles of wood to try to save what we could," winemaker Remy Nodin from Saint-Peray in the Ardeche region of southeast France told AFP.

"We watered, we heated, nothing worked," said Stephane Leyronas, a kiwi grower, in the nearby Aubenas area.

"I used a flamethrower and lit more than 700 small fires which didn't even last the night," he added.