Updated: Jan 25, 2021
Good copper? Bad copper? The debate continues. So here are 7 things you might not know about how copper is used in viticulture. Why 7? Well we like 7 at Château George 7.
1. Copper compounds – most commonly copper sulphate - are used instead of a chemical treatment to protect vines from fungus brought on by humidity: downy and powdery mildew. These are not a problem in winegrowing regions that have a warm, dry climate but they are a definite issue here in Bordeaux. So it is no surprise that copper sulphate combined with lime and water is called Bordeaux mixture aka ‘Bouillie Bordelaise’.
2. Good: It is the most effective weapon against downy mildew for organic, biodynamic and sustainable grape growers who want minimum use of chemicals in the vineyard.
3. Good: It does not penetrate into the plant like systemic chemical treatments but acts on the surface and is washed off with rain. The drawback: It gets washed off with rain! So in wet weather periods, farmers need to keep spraying to protect the vines.
4. Not so good: Once washed off, copper enters the soil and breaks down extremely slowly. It might occur naturally but it is a metal and if it builds up too much it can render the soil lifeless. Plus, like a lot of metals, small amounts are necessary for health but excess exposure is the problem that can cause cell damage and disease.
5. Bad: The European Food Safety Authority (EFSA) say that copper compounds can pose risks for farm workers, birds, mammals, ground water, soil organisms and earthworms. A concentration of copper can cause environmental problems such as water contamination and loss of soil biodiversity. Someone applying the copper should wear a mask or be in a closed tractor and you should not stand around and breathe it in!
6. Early in 2019, limits for copper were reduced to 4kg per hectare (previously 6kg/ha) and ‘smoothed out’ over a 7-year period to allow for more to be used in a very wet year if needed and balanced out by using less in a subsequent year. Initially, the EU did not include this "smoothing mechanism," but France predicted that over half of organic winemakers would return to conventional farming and lawmakers acquiesced. Even so, some growers will not be able to remain organic if we have lots of years in a row with weather like we had in Bordeaux in 2018!
7. Good: This new limit is forcing researchers to find an acceptable alternative quicker. There are biocontrol products (synthetic reproductions of what occurs naturally in plants to fight disease or pests) which can reduce the need for copper by up to 50% but they are not permitted in organic farming in France (accepted in other EU countries). However, algae-based sprays are being tested in Bordeaux. So far, these have proved effective in the lab and are now being tested in the field with mixed results.