1 Notions to know
Copper products have a mode ofcontact fungicidal action : they are deposited on the surface of plant organs. During rain or wetting, Cu ions2 + are released. These ions in solution inhibit downy mildew zoospores. The application of copper must therefore be done in a way preventive, before the rains which will generate contamination. Copper has no curative effect on downy mildew, which is mostly present inside plant tissues and not accessible.
In the event of the presence of symptoms, it will therefore be necessary to continue to carry out preventive applications before new rains to avoid recontamination, because the product will not eradicate the attack already observed.
2 Manage renewals well
Leaching. The copper applied to plant surfaces is rinsed off as the rains follow the application. Copper leaching is not linear: the quantity of copper decreases by half during the first 5 millimeters of rain! It is considered that the copper is totally leached around 20 mm of cumulative rain.
Vine shoot. It leads to the development of new unprotected organs and a general increase in the vegetative surface which can be contaminated. Copper is a contact product. It therefore only protects the organs that received product during the last treatment. It is important to monitor the growth kinetics of the vegetation and the times of strong growth. It is accepted that a shoot of 20 cm from the branches must lead to a renewal.
Downy mildew symptoms. Observing the sanitary condition of the plot is essential. If the plot shows regular symptoms on leaves or bunches, it is necessary to control the secondary contaminations which occur in particular during rains but also during very humid periods (prolonged dews) and consider them as contaminating episodes.
3 Adapt dose according to canopy, stage and risk
Today, the amount of copper metal applied per treatment is still defined empirically. Recently, some tools have been developed to help winegrowers choose their doses. The latter are adapted according to the leaf area but also to the risk (expected rains, phenological stage, etc.). During the first applications, they generally vary between 50 g and 150 g of copper metal per hectare. In full vegetation, during significant risks, the doses used are close to 400g to 500g. It is necessary to be vigilant at the stages of framing of the flowering, sensitive and risky period (where the doses can be a little higher).
To remember
Treating with doses higher than 500 g/ha is of no interest technique or efficiency.
Good to know
The positioning of the treatments comes well before the dose or the formulation of copper in the success of the protection against mildew. All vegetation should be well covered with this contact product. For this, the treatments are carried out face by face (direct or indirect by crossing). It is necessary to apply the product before the predicted contaminating rain and before the vine has developed new foliage. It is therefore necessary to have the capacity to be able to protect the entire vineyard in the day before the rain.
How to deal with extreme conditions?
When mildew pressure is high and the rainfall announced for the week is substantial, it is risky to wait for optimal conditions to intervene. In this situation, a cupric treatment, in the presence of high humidity, or even under a light rain (within the limits of what is authorized by regulation), should be considered. before continuing the protection under better conditions.
Some winegrowers have equipped themselves with quads with mounted or trailed sprayer to be more reactive and lighter, and to be able to intervene where an inter-row tractor could not enter. This type of application is certainly not as good as with a conventional sprayer, but can make up for a critical situation. In addition, the quad is to be preferred over the backpack atomizer, which does not allow you to manage a uniform forward speed. It is also more ergonomic and safer for the person who has to intervene.
4 Effect of copper on the harvest
Additions of copper made during anti-mildew treatments can leave residues in the harvest. Recent work carried out by IFV Occitanie shows that the total amount of copper added to the campaign seems to have little impact on the level of residues found on the grapes. A significant amount of copper last treatment, however, seems to favor the presence of copper at harvest.
During vinification, with non-excessive treatment in the vineyard, no effect on alcoholic or malolactic fermentations has been demonstrated. However, in case of high copper concentration, it has been observed, in indigenous fermentation only, higher latency times.
Good to know
On the other hand, the presence of copper in the musts, particularly in white and rosé, leads to consequences on the aromas of wines with lower productions of esters and acetates and especially of thiol compounds. Carrying out skin maceration makes it possible to minimize the copper concentration of musts with a gain in thiol in most trials.
5 Reducing the use of copper against mildew
The optimization of copper doses through the use of decision support tools and the use of biocontrol products against downy mildew constitute two complementary levers in the search for a reduction in the quantities of copper used.
Decision support tools (DST). For three years, from 2017 to 2020, an experimental network in organic viticulture in New Aquitaine tested the OAD DeciTrait, as part of the Opticuivre trials to trigger treatments and to modulate copper doses. The first results show that dose modulation does not seem to be the most impactful factor in reducing the overall copper dose.
Indeed, it is the processing dead ends generated by the tool’s forecasts that make it possible to reduce the quantity of copper applied. : – approximately 20% in 2019 and 2020.
Biocontrol. Currently, 6 active ingredients classified as biocontrol can be used against mildew. Several years of trials carried out on a parcel of Merlot from the Libourne-Montagne high school, as part of the Alt’Fongi Biocontrol projects (1)have found that sweet orange essential oil and phosphites reduce the use of copper while maintaining equivalent effectiveness at a conventional dose of product.
(1) The Alt’Fongi I and Alt’Fongi II projects are co-financed by the CIVB and coordinated by CA 33, IFV and Eplefpa Blanquefort.
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