In organic agriculture
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Copper is a natural contact fungicide used to protect crops from downy mildew and bacterial necrosis. In organic winegrowing, it is the only approved fungicide for combatting downy mildew. Fungicides based on synthetic molecules are singled out as not meeting social and environmental requirements, and the same also applies to copper. Its toxicity to microorganisms in water and the soil has been well-known for many years. In February 2019, the use of copper metal was capped at 28 kg/ha for seven years.
So how do we reduce the use of copper in organic winegrowing, and thus preserve the soils better without adversely impacting the quality of their grapes?
This is a complex but not insoluble equation. You have to know the best way to time the treatments based on health pressures and rainfall levels. The first treatment is vital for the progress of the campaign, and often enables a reduction in annual copper use. This involves expertise and careful observation on the part of the winegrowers.
Prophylaxis is also vital to reduce copper usage: grape bunches must be in a well-ventilated environment to prevent downy or powdery mildew from developing. This is achieved using sustainable, meticulous leaf thinning, as well as disbudding and shoot removal.
These methods are already widely used by winegrowers, particularly in organic agriculture. What other options are there for further reducing copper usage today?
Recent studies have shown that halving the copper metal doses used has no impact on the effectiveness of treatments in terms of intensity. The ideal option is therefore to reduce treatment dosages even if it means applying treatments more often, until this is wrung out.
Tests are also being performed on the parallel use of alternative methods, such as infusions and brews designed to improve leaves’ natural defences against downy mildew: nettles have antifungal properties, and horsetail combined with silica has a draining effect and thus limits the development of fungal diseases. Finally, in the long term, we can expect the use of varieties resistant to downy and powdery mildew. For example, the RESDUR® and Genovigne® varieties developed by INRA and IFV have genes resistant to these diseases. However, they are not yet permitted for use by PDO specifications.
Additional research is required to further reduce the quantities of copper used, as we must not forget that all of these methods are preventative and therefore still require expertise and vigilance from winegrowers.
By Pauline Milon and Clément Maës – oenologists