Copper and the Cost of Survival

The contradictions and compromises of organic viticulture’s most trusted fungicide

Life is full of contradictions.

We celebrate innovation while romanticising the past. We want progress, provided nothing changes, and we want to work with biology, right up until it becomes inconvenient to do so, or threatens our crops.

Wine of course is no exception. Tremendous focus is placed on the wine’s connection with nature, its authenticity and the value of living soils, yet there is no hiding from the fact that the wine we drink is more often than not the product of decisions and compromises made on the basis of economic requirements first, with what is best for both the wine and the land it grows on being of secondary concern. It is an understandable order of priorities when considering how important cash crops like grapes are for the producers livelihood, but it is nevertheless something that is rarely discussed openly. One stark example of this is the use of fungicides. In Europe, viticulture accounts for a mere 3.3% of all agricultural land, yet it uses 86% of the total fungicides consumed. According to data released by Eurostat for 2023 (released April 2025), inorganic fungicides accounted for 62.9% of the category called ‘fungicides and bactericides’ sold in the EU. These inorganic fungicides refer to copper compounds, inorganic sulphur and other inorganic fungicides, many of which are also permitted in organic farming.

What I want to take a closer look at in this article is the widespread use of copper based fungicides. In particular we will explore why they are needed in the first place, why they work so well, and whether a metal that irreversibly accumulates in the topsoil of a vineyard can truly be considered in line with the broader ecological aims of the organic and regenerative farming movements.

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The Arrival of Mildew

If you’ve been subscribed for a while, you may remember a previous deep dive I did into the many ways powdery mildew, or Erysiphe necator to give it its proper name, has shaped modern viticulture. I won’t go into as much depth here, but nevertheless a brief re-introduction of this type of viticultural foe is in order. First noticed on European shores by an English gardener called Edward Tucker in 1845, E. necator is believed to have originated in North America where the pathogen existed on wild North American Vitis species. Despite efforts to contain it, the malady quickly spread throughout Europe, having been observed in France as little as two years after it was discovered in England. From there on there was no stopping it, for Vitis vinifera is particularly susceptible to the fungus, while its spores can travel significant distances when carried by favourable winds. Needless to say, E. nectator continues to plague European and international viticulture to this day.

Thankfully, the discovery that lime and sulphur were effective remedies for powdery mildew was not far off. Similar problems had long plagued fruit orchards, and it took only a small leap of imagination to try the treatment on vines. Following some initial hesitancy by farmers, it was by as early as 1853 common practice to apply sulphur throughout affected regions.

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The Uninvited Guest: How powdery mildew shapes viticulture

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While a workable solution had been found for E. necator, its arrival on European shores was soon followed by another North American import. Plasmopara viticola, commonly known as downy mildew or peronospora, was first discovered in France’s Gironde region, near Coutras, in 1878. Where sulphur had worked wonders for powdery mildew, it had little to no effect on downy mildew. Considered one of the most devastating diseases of the grapevine in climates with relatively warm and humid summers, it wasn’t long before growers in places like Bordeaux, where conditions for the malady are superb, were in despair.

The breakthrough came when Pierre-Marie-Alexis Millardet, a professor of botany at the University of Bordeaux and among the pioneers of plant pathology at a time when the discipline barely existed, noticed that vines along the roadsides of Bordeaux, daubed with a mixture of copper sulphate and lime to discourage theft, appeared strikingly free of disease. Intrigued, he began a series of experiments that would soon formalise the formula and give birth to what became known as the Bordeaux mixture, a carefully balanced blend of copper sulphate and hydrated lime mixed with water to make the metal both effective and tolerable to the vine.

Pierre-Marie-Alexis Millardet

By 1885-86, this mixture was being promoted and quickly gained enormous popularity and widespread adoption. By the 1890’s it was standard practice in most of France and becoming gradually implemented in Spain and Italy, becoming normal practice anywhere where downy mildew was considered a threat. It is also used to this day, and if you have walked a vineyard after it has been sprayed, you may well have noticed a blueish tint on the leaves, a tell tale sign of the use of copper sulphite. With downy mildew representing a persistent and recurring threat, it didn’t take very long before it evolved from what might have been considered an emergency measure to protect vines, to a routine preventative measure applied regardless of prevailing conditions and actual disease pressures.

Why Is Copper So Effective?

Simply put, copper works because it is chemically reactive in a way that living cells struggle to defend against. When copper salts are deposited on a leaf surface and moisture is present, tiny amounts of copper ions are released. These ions readily bind to proteins, fats, and genetic material inside fungal, bacterial, or other living cells. In doing so they disrupt the structure of enzymes, puncture membranes, and interfere with the basic chemistry required for respiration and growth. Unlike many modern fungicides that target one specific metabolic pathway, copper acts at multiple sites at once, which is why it has remained broadly effective for well over a century, preventing any organism from developing immunity.

Micro-organisms rely on carefully balanced internal chemistry, which copper overwhelms and disrupts. It can catalyse reactions that generate highly reactive oxygen species, effectively microscopic biochemical shrapnel, which damage everything from cell walls to DNA. For a pathogen trying to germinate on a wet leaf, this is catastrophic. However, copper exhibiting what we may call non-selective toxicity can be problematic. It does not distinguish between harmful fungi and the wider microbial life that growers would benefit from protecting, and has the potential to damage the vine itself. At high enough concentrations copper applications disrupt photosynthesis, denature enzymes, and promote oxidative stress. This is why excessive copper sprays can produce visible phytotoxicity with symptoms like leaf burn, russeting, delayed growth, or reduced yield.

Downy Mildew

However, a vine is a large, multicellular organism with structural redundancy and defence systems. Waxy cuticles, cell walls, and detoxification mechanisms in the apoplast and vacuole can immobilise or compartmentalise part of the incoming copper load. In other words, while some cells may be sacrificed, the plant as a whole usually survives. For a fungal spore or a bacterial cell however, there is no such margin for error. If the membrane is damaged, a few enzymes get disrupted, or oxidative reactions are triggered, the organism stands no chance of survival, as the pathogen’s scale offers no buffer. For the vigneron, there is a relatively beautiful brutality to this mechanism, and it is wonderfully effective.

That copper salts are naturally occurring, and not a product of modern synthetic chemistry, has also afforded it widespread acceptance among organic certifiers. It is however derived from mined minerals, and its acceptance inside organic farming is perhaps best understood as a pragmatic concession stemming from a time where no practical alternative was available, a position that is still broadly held.

What Happens to Copper in the Soil?

Of course, anything applied to the vines ultimately ends up in the soil. It is here that the use of copper becomes contentious. Being a metal, it doesn’t degrade like an organic molecule, and once it is in the soil it tends to persist for a significant amount of time. Most vineyard soils bind copper quite strongly. Clay minerals, iron and manganese oxides, and organic matter all provide charged surfaces that grab onto Cu²⁺ ions. Over time the metal accumulates primarily in the upper horizons of the soil where sprays land (0-30cm down). Because of this ability to bind with common soil components, a large fraction of applied copper is effectively locked in place. A study by Droz et al. (2021) found that net accumulation dwarfs net exports across the European Union, with average net export ~0.29 kg Cu/ha versus net accumulation ~24.8 kg Cu/ha over time. In other words, only a small trickle leaves annually with the rest building up.

When copper does move, the dominant pathway is often erosion and runoff of fine particles. The above mentioned paper notes that copper in topsoil is largely particle-bound (they cite ~85% in suspended particles), so rainfall events and slope can export copper attached to sediment, with leaching as an additional pathway depending on soil chemistry. Mobility is strongly shaped by pH and redox/moisture conditions with wetter, potentially more reducing conditions being able to shift copper into less mobile forms/complexes, while drier, more oxidising conditions can favour forms that are more mobile. That said, drier conditions can also increase binding strength via changes in organic matter chemistry and higher pH. That is to say, copper’s behaviour is not uniform and depends on the interaction of climate and the binding capacity of the soil in question.

Map of topsoil Copper concentration (mg Kg^-1) - Source: European Commission

This means that the risk of creating soil copper “hot-spots” is a consequence not only of application rate, but also the soil and climate in which it is applied. This also matters for any thoughts of remediation as, due to copper not being degradable and remediation options like phytoextraction (plants absorbing copper through their root system) is of limited effectiveness, the only viable lever available to farmers consists of reducing future inputs and reducing erosion/runoff (to limit off-site contamination).

In this regard, to the dismay of some growers, the regulatory bodies are one step ahead.

Regulations and Implications

In 2018, the European Commission adopted the regulation (EU) 2018/1981 to restrict copper use in agricultural soils. This regulation implemented a maximum application rate of 28 kg ha^-1 of copper over a period of 7 years, which averages out to 4 kg ha^-1 year^-1. This was done with the explicit purpose of minimising potential soil accumulation, and the exposure for non-target organisms, while being mindful of the reality faced by growers encountering disease pressure. While restrictive, it is by no means excessive and for France, data from the ITAB Institute (Technical Institute for Organic Agriculture and Food) shows that French organic growers used an average of just 3.72 kg/ha in 2024. What’s more, that was a year plagued by heavy rains in many regions. On that basis, it appears that farmers are broadly speaking willing to go above and beyond the restrictions put in place by the European authorities.

Yet, even so, as was shown above, these levels still result in the gradual accumulation of copper in vineyard top-soils. On top of this, citing health concerns for workers applying copper based fungicides, French authorities have recently gone one step further, with the national health and safety agency ANSES, (Agence nationale de sécurité sanitaire) revoking market authorisation for 19 widely used copper-based fungicides. This is now in effect and the products can as of the 15th January, 2026 no longer be bought or sold, with farmers having one year to use existing stocks.

As you can imagine, this has created quite the uproar among the organic farmers affected. In an article on the topic by WineSpectator, Gérard Bertrand, a leading vigneron and advocate for organic farming in southern France was quoted as saying:

“Copper is a natural element, naturally occurring in nature; to get to toxic levels, you have to use much larger quantities. It’s a lot of noise for nothing.”

Yet while the sentiment is clear, particularly in the face of a lack of alternatives, the above statement depends on whether the toxicity discussed pertains to the soil biome or the workers in the field. If the former, it is a misunderstanding that much larger quantities are required for toxicity, as toxicity in the top-soil increases over time, despite annual inputs being below the allowable threshold imposed by the EU. Given the fact that ANSES justified the ban on these preparations on the grounds that the manufacturers had not provided sufficient worker safety data, however, Monsieur Bertrand’s statement must be viewed in the latter context.

Copper preparation on vine leaves

Notably, officials in other wine growing nations in the European Union have disagreed with the ANSES decision, and the EU has extended copper use authorisation until mid-2029.

The risk of course by such a broad handed push to make vineyards healthier, in an environment where many growers rely on some form of copper based remedy to combat mildew disease pressure to remain viable, is that many will revert to the various synthetic alternatives that are still permissible for use. The WineSpectator article linked above states that industry estimates suggest that 20 percent of organic vineyard land could lose certification due to inability to control mildew without adequate copper options. That is certainly a step in the wrong direction.

That said, it appears clear that better solutions are required to make vineyards facing downy mildew pressure truly sustainable.

What Are the Sustainable Alternatives to Copper?

Few and far between is the simple answer.

There are products out there that rely on microbial antagonists, using organisms such as Bacillus subtilis or Trichoderma with the aim to out-compete or inhibit pathogens on the leaf surface. These may produce antibiotics, occupy infection sites, or stimulate the vine’s own defences. Unfortunately they tend also not to be anywhere near as effective as copper based products.

Similarly, there exists a group of remedies called resistance inducers or elicitors, which aim to stimulate the plant’s own defence mechanisms. Notable among these is a polysaccharide extracted from brown algae called Laminarin, which triggers a vine’s immune response system by looking like a fragment of a fungal invader.

Another remedy in this group is Potassium phosphonates, which are salts of phosphoric acid, which due to acting both on the mildew directly as a contact fungicide, while also priming the plant’s immune systems for defence are highly effective, particularly in the early stages of infection. They do however occupy a regulatory grey zone due to the fact that they are systemic, moving within the vine rather than remaining on the surface and can persist in plant tissues and may ultimately be detectable in grapes and wine. While a natural product, this behaviour distances it from conventional organic thinking and has struggled to gain widespread recognition among certification bodies as a result. Nor is immune activation free. Diverting energy toward defence may come at the expense of growth or ripening, particularly when the plant is already under stress.

Thorvald in action.

UVC based applicators, such as the ingenious Thorvald arrays from Saga Robotics that irradiate vines with a strategically timed dosage of UVC radiation to kill powdery mildew may also be of some use, however its efficacy is unlikely to be as high for downy mildew. This is because where powdery mildew sits superficially on the plant, downy mildew infections occur inside the plant tissue and will thus be shielded from the majority of the radiation. That said, there is good reason to be excited about this approach regardless, particularly for larger vineyards that can accommodate this form of robotic intervention. By using it as a preventative measure, it should be possible to reduce the disease pressure to a point where copper-based inputs used in conjunction with the UVC treatment can be dramatically reduced. This is however, at best, a niche solution, and out of reach for most cash flow constrained farmers battling mildews.

Final Thoughts

The contradiction that the most reliable defence against downy mildew remains a substance that, by its nature, persists indefinitely in the soil is hard to avoid. Copper saves harvests. It has done so for nearly a century and a half, and without it many regions would struggle to produce wine in difficult years.

And yet the bill accumulates. Every application, however modest, shifts a little of tomorrow’s soil health into today’s security. The accumulation may be subtle when viewed from one vintage to another, but over the course of decades it is not.

In a further twist of irony, it is often the case that those most aware of the issue are also those most committed to working with nature. Organic and regenerative growers did not choose copper because it was perfect, but because it works, because it exists, and because the alternatives remain less reliable, less affordable, or entangled in their own compromises.

Being cognisant of the issue, aiming to reduce inputs where possible, while striving to develop new and better methods is really the only way forward. Until then, copper remains what it has always been, a compromise.

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