Alternatives to Copper in Organic Viticulture

Biodiversity Pruning and training of the vine Precision agriculture Grape varieties

Copper is used in agriculture, particularly in organic systems to control various fungal or bacterial diseases. It is notably used in the form of Bordeaux mixture in viticulture, arboriculture or market gardening. Naturally present in the soil, it is allowed in organic farming (OF) and represents the only active substance with a fungicidal effect and broad spectrum of action.

However, the identification of negative effects of copper on the environment (soil, biodiversity) and the resulting regulatory restrictions push research and winegrowers to find alternatives to copper treatments.

Major use of copper

In organic viticulture, copper is mainly used to control downy mildew of the vine and bacterial necrosis for which it is approved, but its efficacy is also recognized in cases of black rot on vines.

Copper is mainly used in its ionic form (Cu2+) and sprayed on the aerial parts of the vines; however, it can also be applied locally on wounds or on the soil.

Regulation

In 2019, the maximum authorized dose of copper in organic viticulture was reduced to 4 kg / ha / year. Exemptions exist in years with high downy mildew pressure. In the case of an exemption, the copper dose must not exceed 28 kg over 7 years.

Already banned in several European countries (Netherlands, Scandinavia, Germany) in organic farming and conventional agriculture, legislation regarding copper continues to evolve.

Alternatives to copper

In response to the highly tense context of copper in organic viticulture, various alternatives have been identified, both by research institutes and by winegrowers.

Methods with direct action on the pathogen

These methods act directly on spore germination or pathogen development.

Natural preparations with biocidal activity

It is possible to treat vines with plant extracts.

These preparations, often of complex composition, have a biocidal activity on pathogens but can also act as plant defense stimulators (PDS).

The following products are authorized in organic viticulture (2017 data):

The potassium bicarbonate, of which two preparations are authorized on the market - Armicarb and K-BLOC -, significantly reduce vine diseases. The efficacy is greater when the product is applied close to the disease inoculation period.
horsetail has shown its effectiveness against downy mildew of the vine in cases of low disease pressure, and in combination with a reduced dose of copper.
The nettle manure, praised by many publications, showed effectiveness only in a 1990 study demonstrating moderate efficacy against normal downy mildew pressure.
Commercial preparations based on citrus essential oils are authorized in OF for applications on vine downy mildew.

Direct biological control by organisms

Biological control by organisms involves microbiological biocontrol agents. Organisms that can reduce copper treatments can be fungi, yeasts, bacteria, or viruses. They act through various modes of action:

Direct inhibition of the pathogen
Competition for nutrients or space
Interaction with the pathogenesis process

In France, few microorganism-based products are marketed: only 11 have authorization. Among them, only two products allow control of diseases in organic viticulture:

Esquive uses an actinomycete (strain I-1237 of trichoderma atroviride) to fight against grapevine trunk diseases
Roméo uses a yeast (cerevisane cell walls) to fight downy mildew

Use of plant resistance capacities

Resistant varieties

There are new resistant varieties registered in the Official Catalogue allowing reduction of copper treatments, notably the following grape varieties:

Artaban: Red variety, total resistance to powdery mildew and strong resistance to downy mildew
Vidoc: Red variety, total resistance to powdery mildew and strong resistance to downy mildew
Floreal: White variety, total resistance to powdery mildew and strong resistance to downy mildew
Voltis: White variety, total resistance to powdery mildew and strong resistance to downy mildew

Implementation of prophylaxis

Prophylaxis aims to limit primary contaminations of the pathogen. It consists of physical and agronomic practices that reduce the application of fungicides by establishing preventive practices in vineyard plots.

Physical protections

Among the physical protections available to limit vine contamination by the pathogen are:

The Viti-tunnels (or rain covers): these waterproof and retractable covers created in 2018 by the startup Mo.Del offer rain protection to vines and thus limit the risk of contamination by downy mildew, black rot, and esca, three diseases related to humidity on vines. These waterproof nets provide optimal aeration to limit condensation. Equipped with wetness sensors and rain detection radars, the Viti-tunnel automatically deploys to prevent rain from falling on the vine stocks. The device also allows confined spraying of sulfur powder to fight powdery mildew if needed. As envisioned by its creators, the Viti-tunnel allows a significant reduction in the use of phytosanitary products and pesticides and helps maintain crop yields in case of high disease pressure or climatic accidents.

Strategies to reduce copper doses

Various strategies to reduce copper doses can be imagined, considering the alternatives currently available to winegrowers.

Prototype 1: mainly relies on a direct reduction of copper doses, supported by Decision Support Tools (such as Mildium) to optimally choose doses, intervention dates, and spraying systems.

Prototype 2: The reduction of copper doses can be enhanced by the addition of Plant Defense Stimulators or biocidal preparations, which can replace some copper treatments.

Prototype 3: The goal of a "zero copper" protection must necessarily mobilize, besides the biocontrol solutions of prototype 2, the use of grape varieties resistant, as well as prophylactic interventions, such as microclimate management through pruning and removal of infected litter by collection.

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