The Bordeaux mixture
Most wine lovers know what a Bordeaux blend is, but what about the Bordeaux mixture? The former is a popular wine style emulated throughout the world, from Tuscany and California to Chile and even Ireland. The latter is something quite different indeed and not some combination of Cabernet and Merlot, but rather a preventative fungicide permitted in organic and biodynamic viticulture.
What is the Bordeaux mixture?
The Bordeaux mixture, or bouillie bordelaise to give it its French title, is a preparation used in viticulture to control downy mildew, as well as other fungal and bacterial disease. It’s an approximate 10:10:100 mixture of copper sulphate, lime and water. Winegrowers apply it in spray form, and it has long been recognised as an effective preventative measure against disease.
Where did it come from?
Well, Bordeaux. More specifically, it arose as a result of research at the University of Bordeaux late in the 19th century. Following the outbreaks of phylloxera, mildew and other fungal diseases in the region, a professor at the university set out to find a solution.
The Bordeaux mixture is sometimes known as the Millardet-David treatment, in reference to the two men credited with its discovery. Alexis Millardet was the professor in question, and his trials and tests were carried out at Margaux estate Château Dauzac. Millardet was assisted in his work by Ernest David, Dauzac’s technical director.
What does it do?
Traditionally, the Bordeaux mixture is sprayed on the vines during winter. Its effect is to prevent and control the spread of downy mildew in particular, and numerous other diseases. The mixture stains the vines – and anything else it comes into contact with – blue. It has the benefit of not being easily washed away by rain, the precise moment when vines are particularly under threat from mildew.
In the long run, the mixture can have an adverse effect on the vines and soil, as the level of copper can become toxic over time. Excessive amounts of the Bordeaux mixture can thus be harmful to soil bacteria, earthworms and fish, as well as livestock and humans.
The Bordeaux mixture in organic wine farming
In conventional farming, the Bordeaux mixture is no longer used to the extent that it once was, with synthetic alternatives seen as preferable for most producers. Organic viticulture doesn’t allow synthetic fungicides, making the Bordeaux mixture and other copper-based treatments key in the organic winegrower’s toolkit.
Though permitted in both organic and biodynamic farming, some producers opt to limit or eschew use of the Bordeaux mixture altogether. Copper toxicity is a threat to natural life – seemingly at odds with the biodynamic philosophy – and spraying too close to harvest time can have an adverse effect on the wine’s quality and even impede fermentation.