From about mid-April, Europe has experienced sub-zero overnight temperatures which have caused damage for the second consecutive year, especially in the regions of Champagne, the Loire Valley in France and the Piedmont region in Italy. Several other wine producing regions, including Bordeaux, Alsace, Belgium and the Rheinhessen in Germany have also been partly affected! Many are calling it the worst frost since 1991, as temperatures dropped to nearly 26° F in some regions.
Grapes like Chardonnay, Nebbiolo and Malbec, and to a certain extent Cabernet Franc and Pinot Noir, are very sensitive to frost and if the buds are frozen, the vine normally produces secondary buds which will not produce any fruit. However, Cabernet Sauvignon and Merlot may reproduce buds with approximately 30 to 50% fruit productions possible.
There are various ways to protect your vineyards against frost:
- Location: When setting up a new venture it is important to choose a location which is not susceptible to hard frosts, preferably without gullies and hollows. Avoid windbreaks that hinder airflow including windbreaks across the bottom of the vineyard which traps cold air causing it to bank up.
- Soil type and moisture: Dark soil absorbs more heat than light soils and gravel soils absorb more heat than clay soils. Soils that absorb more heat are less likely to be frost prone.
- Variety selection: Spring frost damage is not the only consideration and variety selection is important. Earlier bursting varieties are more likely to be affected by frosts than later bursting varieties.
- Timing of Pruning: Bud-burst can be delayed by late pruning and this can reduce the risk of frost damage.
- Overhead Sprinklers: Overhead irrigation is the most commonly used method of frost protection in vineyards. There are many system designs, but all depend on two factors, namely when water freezes, the formation of ice releases energy and irrigation water is usually significantly warmer than the surrounding air. This method has three disadvantages however, as there may be significant damage caused by the inability of the vine to support the additional weight leading to major vine damage, this method can waste considerable amounts of water and the systems relying on sensors activating an alarm require 24 hour maintenance and attention.
- Fire: This is the oldest system developed almost 80 years ago in Chablis and can be used by making fires surrounding the vineyard or placed the fire inside the vineyard between the rows of vines. The heat created by the fire pushes the cold air above the vineyard. It is efficient but demands high maintenance during the frost period and can cost approximately R25 000 in fuel per hectare per night.
- Wind turbines is also a very efficient system but very costly as an investment at approximately R350 000 per ha. The positive here is that the turbine can be used over a period of 10 to 15 years.
- Helicopters have also been used in Montlouis in the Loire Valley this year. It is a process which Château Haut-Brion has been using it for over 40 years. The pilots’ base their flight pattern on a GPS signal linked to temperature sensors placed amongst the vines. It is very efficient if the helicopters are on standby next to the vineyard. The effect is that the turbulence created by the helicopter move the cold air above the vineyards. The cost however is over R2 500 per ha per hour.
- Frost treatment is a substance of sweet chromatograph solution that is used, still in its experimental phase and works only at 2-3 degrees. Secondly not all cultivars reacts the same to this method, because as you spray the sweet solution when the temperature drops over the buds, it freezes at lower temperatures.
Despite the unfortunate occurrence of frost in some of the most prized wine regions of the world, it is a testament to viti- and viticulturist’s that they are still able to produce consistently good and even excellent quality wines every year.