With cold spells and spring frost, the vines are subject to very low temperatures. Spring frosts can reach -9°C. The vines risk losing their buds and winegrowers risk losing production. Crops can be lost because they are frozen. Here are some tips to fight against the freezing of vines, and hope to limit the damage.
In spring, when temperatures rise, the first leaves and buds appear. The buds can withstand temperatures down to -3°C, but beyond that, they risk freezing: the sap, rich in water, will freeze, and "burn" as the winegrowers say in the embryonic tissues of the flower or leaves. This is what causes the death of several parts of the plant.
If you can't impose your law on nature, it's about limiting the damage. To fight frost, the air around the vines must be warmed up. The idea is to prevent the temperature from falling too low: and for this reason the winegrowers are working to heat the air, or to prevent the vines from cooling down further.
One of the most common practices is the use of candles. This method consists of placing large candles in the vineyard, paraffin blocks in metal boxes. The wax of candles is natural. Another trick is the constitution of braziers, placed in the middle of the vines. The candles and braziers will warm the ambient air around the vines, and thus prevent a too high temperature drop. Another tip is recommended here: you can also have heated fans to circulate the air, and allow the heat to be distributed evenly. This prevents freezing.
The only problem with candles: there is only one company in France that produces them, it quickly finds itself out of stock.
The use of heaters is also widespread: they are placed between the rows of vines and thus make it possible to gain up to 3°C. The company, like candles, requires a large workforce in the layout of the heaters.
The use of heaters offers a beautiful night show, but is not very environmentally friendly. Indeed, this practice emits carbon dioxide.
Spraying consists in spraying the vines with water. Thus the buds are caught in an ice pocket without the water they contain freezing. This is called the supercooling phenomenon. This technique is delicate, because the ice cube must not thaw too quickly. Thus it is necessary to water the plots until the temperature becomes positive again. The spraying is therefore continuous.
This system is considered efficient but requires substantial installations: pipes and sprinklers are very expensive. This is why this system is often reserved for the most exposed plots.
It is a more affordable, automated and less polluting method. This involves using propane burners in the vineyard to heat the air. It is necessary to count 150 burners per hectare.
They are used here as air stirrers. Indeed, these small 11m high wind turbines, by stirring the air, will direct the air above the vines towards the vines. This air, a little warmer, then allows the vines to be warmed up.
Finally, some winegrowers use helicopters to brew the air. The helicopter flying at low altitude (i.e. below 20m) brews and heats the air above the despicable. The air in the vines is therefore warmer, which prevents freezing.
This operation remains dangerous, since it is carried out at dawn, so with little light. It is also expensive, since it costs 170 euros per hectare. However, it is a method that works and is profitable, since it could effectively protect a vineyard.
Marie Lecrosnier-Wittkowsky for Les Grappes