Le cuivre dans la viticulture biologique : pour ou contre ?

Copper in organic viticulture: for or against?

Recognized as natural, copper-based treatments are used against diseases such as downy mildew or bacterial necrosis, two of the most common diseases in the wine industry. And they are used in particular in organic agriculture, because authorized by regulations. But what is its real use? And above all, is there a hidden problem with this type of treatment?

The use of copper in viticulture

First of all, you should know that copper is only a preventative product. In fact, it will intervene in the metabolism of the vine itself by strengthening its defenses. The copper-based treatment is applied at the end of winter, or at the very beginning of spring, just before vegetation resumes.

Small downside on this type of treatment: a significant part of the copper, between 30 and 40%, is washed away after about twenty minutes of rain. It is necessary to repeat the treatment a certain number of times to make it as effective as possible.

What do the regulations say about the use of copper in viticulture?

Copper is naturally present on our planet, of course. However, copper in viticulture creates controversy because it is considered too polluting. Depending on the doses of copper used, it can be very toxic to microorganisms present in the soil. Another significant concern: it is not biodegradable, or very little. There will therefore always be a trace of copper in the environment where it was once present.

Recently, copper has been the target of European authorities. Indeed, in February 2019, new European regulations were introduced, requiring a reduction in the use of this metal. To give you some figures: before this new rule, winegrowers were authorized to use copper at a rate of 6 kg per hectare per year, and this smoothed over 5 years. That is to say a modulated use over 5 years which does not exceed 30 kg per hectare. However, since February 2019, this use has been limited to 4 kg per hectare per year, this time smoothed over 7 years. We must no longer exceed 28 kg per hectare over 7 years. A toughening which has not only made people happy, but which, for sure, is a good thing for our environment.

But why ? Why is copper in viticulture dangerous? Copper binds to plants and microorganisms in the environment in which it is found. And because it is non-biodegradable, it never really disappears. This being said, it remains in its relatively close environment. It therefore never enters groundwater, which is still good news. However, it accumulates and destroys the soil, potentially making it almost sterile in the long term. This is clearly seen in areas surrounding industries releasing copper. In fact, very few plants manage to survive and grow there. But copper can also poison animals. Sheep, for example, whose copper poisoning occurs even at low doses, suffer greatly from the harmful effects of this metal. It also has a devastating impact on earthworms living in the soil, and seriously influences the decomposition cycle.

A priori, there would be no risk to humans drinking wine that has been treated with copper. The toxicity threshold in humans is approximately 10 mg/day. We would have to drink a few liters of wine per day, and for several days, before seeing the toxic effects on our body. Concretely, we are more likely to suffer from it through food (main source of exposure to copper) and running drinking water.

As you will have understood, the concern to be had is mainly about the environment and biodiversity .

And in organic farming?

As we mentioned in the introduction, copper treatments are authorized in the specifications for organic farming. However, the authorized doses of copper are already well below the standards authorized in traditional viticulture. As a reminder, the standard implemented in 2019 limits the use of copper to 4 kg per hectare per year, smoothed over 7 years. Or a maximum of 28 kg of copper per hectare over 7 years. Organic winegrowers were not impacted by this new regulation, since the specifications already required lower doses of copper. The limit is already 3 kg per hectare smoothed over 5 years , that is to say no more than 15 kg per hectare for 5 years .

There is a “but”. Indeed, the latest report from ANSES (the National Agency for Food, Environmental and Occupational Safety) published on March 17, 2020, reveals some surprising data. The figures mentioned were collected in 2016, even before the new European regulations appeared. The quantity of copper used per hectare would be two to three times higher in organic agriculture than in conventional agriculture . Copper is used on 98% of vines in organic farming, while it is only used on 85% of vines in conventional farming.

Finally, of the 957 tonnes of copper used on vines in 2016 , 174 were used on vines in organic farming. This represents 18% of total copper use, while at that time only 9% of French vineyards were organically farmed.

In its report, ANSES estimates that if we achieve the objective of having 15% of French wine-growing areas in organic farming, this would have a significant impact on the use of copper. In fact, this would lead to an increase of nearly 140 tonnes of copper , or +14% compared to 2016 . This is surely due to the fact that copper is a substitute for other treatments and pesticides, themselves prohibited in organic farming. Organic viticulture thus falls back on copper. But, ultimately, is copper in viticulture a good or a bad thing?

In conclusion, it is true that copper is a natural element. And it is surely much better than the majority of pesticides. But it is still important to keep in mind the toxic aspect of copper. And to have a reasoned and controlled use of this heavy metal, very little biodegradable and highly toxic for its environment.

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