Imagine turning a key to a magnificent Andrew Marvell-esque garden. Luscious clusters of fruit crush themselves into open mouths. Nectarines and curious peaches fall into waiting hands. Not a speck of mould or rot. But deeper in the garden is a patch of dead soil, where only infections thrive. This is the garden of ill-judged agrochemical use.
Almost all treatments worth their salt have a downside and winegrowers are coming to terms with the need to find a better balance between positive short-term results and negative long-term ones. Ironically, just as they are ramping up the search for less toxic treatments – particularly for increasingly aggressive fungal diseases – vintners face the risk of losing what has been their softer option: copper.
The copper challenge
Despite its reputation as a more environmentally friendly fungicide, fears have been growing that copper might have downsides as significant as some of its synthetic cousins. The jury is out, however, on what exactly the downsides are. Some fear copper drives out the earthworms and microorganisms essential to soil health. Others say the main worry is simply that while we know copper accumulates, we don’t know what that accumulation does to fauna and flora. Whatever the view, copper’s ability to help control three of France’s most challenging vineyard fungal infections – mildew, botrytis and oidium – makes it an essential weapon for all winegrowers, not just organic growers.
Of the three, mildew – accidentally imported from the US in 1845 – has been the most difficult to treat because European vines were originally defenceless against it. It also has particularly bad associations for the French, having wiped out about 80% of the country’s 1854 harvest, which led to a doubling of wine prices. In 1884 a reliable cure was finally developed at Bordeaux’s Château Dauzac: the bouillie Bordelaise (Bordeaux mix), a combination of copper sulphate, slaked lime and water.
Since then, synthetic fungicides have arrived on the market. Typically, they fall into two main categories; contact products, which stay on the surface, and penetrating or systemic products, which enter the plant. Although contact products are less invasive and imply almost no risk of residues in the final product, their main disadvantage is they can be washed off in rain. That means more tractor miles to reapply them and that they end up in the soil. If they are not biodegradable, they accumulate.
For the EU, accumulation is the main problem, one that risks seeing copper – a contact product that should ideally be applied prior to a fungal outbreak – withdrawn from use in the bloc as of December 2025. Copper usage limits have tightened. Fifteen years ago the norm was about 35kg per hectare. Today the limit is 2-6kg per hectare, depending on fungal virulence.
Asked about copper and the best treatments against vineyard fungi, particularly mildew, Laurent Charlier, head of research for the Bordeaux Wine Board (CIVB), says there is no single best product. That’s partly because so much depends on individual harvest and estate conditions. And partly because growers always aim to use a range of different products, including copper, to reduce the risk of creating resistant infections. Charlier additionally points to a perhaps often overlooked advantage of copper: despite more than a hundred years of use, it does not appear to generate resistant infections.
By contrast, synthetic suppliers are continually scrambling for new molecules. In an e-mail, BASF France said several ingredients active against mildew have developed resistance. This is mainly due to “heavy disease development and pressure”. To address the issue, the company is “looking to develop new fungicide modes of action”, it said. Asked what its bestsellers are when it comes to vineyard fungi, BASF was less equivocal. They “include products based on dimethomorph, metiram, Initium and Romeo to control downy mildew”. while “products to control powdery mildew are based on metrafenone, sulphur and Xemium”.
To combat both accumulation and resistance issues, many growers now use a system of copper micro-dosing, often in conjunction with newer, more environmentally friendly biological control (biocontrol) products. These include herbal and seaweed sprays or bacteria that, in one way or another, make life untenable for unwanted fungi. Some find this system useful, others less so. All agree that it is more work.
In an unhappy twist of timing, just as copper is at risk of being banned, winemakers are increasingly depending on it. And not just because of resistance issues.
Other drivers include rising consumer demand for organic food and wine, as well as changing weather patterns that favour the warmer, wetter conditions fungi love. To say nothing of France’s much vaunted political goal of drastically reducing the use of all agricultural pesticides.
All told, this means a once fairly binary debate (copper good/chemical pesticides bad) is evolving in two directions. Can winegrowers, of all stripes, live without it? And how toxic is it exactly?
What else is available?
The first question has a relatively simple answer: doing without copper would be tricky for everyone, but almost impossible for organic or other growers that limit synthetic pesticide use. The only ways forward appear to be continual copper reduction by deploying a greater mix of treatments, and/or switching to mildew-resistant grape varieties.
That switch sounds ideal but has two drawbacks. First, growers fear loss of flavour and aroma profiles. They are therefore reluctant to undertake a major replanting before they are fully satisfied about quality. Second, from a regulatory standpoint, it could take a decade or two for EU and local vineyard planting regulations to be updated.
The answer to the other question is even harder. “We have a lot of work to do still to find out how to best manage copper levels in soil, and to find out at exactly what point it becomes toxic,” says Stéphane Becquet. Becquet is an agricultural engineer and winemaker who works with Bordeaux’s organic winemakers and the Institute of Organic Agriculture. “You can have soils with very high levels of copper that have no fertility problems. And you have some with very low levels of copper that have fertility problems,” says Becquet. At the same time, copper toxicity levels vary in relation to the level of organic material in the soil. “Broadly speaking, where there is more organic material there is less toxicity.”
Adding to the challenges, Becquet takes issue with the current toxicity measurements used by the French Agency for Food, Environment and Occupational Health and Safety (ANSES). “To evaluate the toxicity, ANSES used a model they used for synthetic molecules, and it does not compare correctly to copper.”
The director of wine and vines at the Gironde Chamber of Agriculture, Laurent Bernos, agrees the subject of copper toxicity is open for debate but notes: “Worms can be found in organic vineyard soils and in the soils of estates that are not organic. So the micro-life is there and the microflora seem to adapt.”
While all agree that copper concentrations become toxic at some point, Bernos says that point depends on plant and soil types. “What is toxic in terms of copper levels for wheat is not the same for vines.” For soil types, he echoes Becquet’s view that higher levels of organic material mean lower copper toxicity. He goes further: “More acidic soils tend to have higher copper toxicity, while clay ones are less so, for example. It is very complex. That means in some areas we might be able to use different doses depending on soil type.”
Plant possibilities
Asked what lies ahead, Bernos agrees that resistant varieties are the main hope. “They might make this whole debate about copper redundant in the next 20 years,” he says optimistically.
In Champagne, the story is much the same. “We try to use the softest treatments possible, the ones that are best for the environment,” says Arnaud Descôtes, technical and environmental advisor for the Champagne Board (Comité Interprofessionnel du Vin de Champagne or CIVC.)
But, having tested about 50 biocontrol products, mainly for mildew, he says the reality is that the results are weak and effects patchy. “The best treatment remains the bouillie Bordelaise and chemical pesticides. But we also use biocontrol combined with copper micro-doses.” As to resistant varieties, Descôtes agrees that it might be 2028 or 2030 before they are available to producers.
French winemakers are prioritising a range of other techniques in their fight against fungi. One is improving the timing of applications. “Timing is everything,” and a good weather service is essential, says François Bréhant, technical director of Bordeaux’s three Barton family estates, Château Léoville Barton, Langoa Barton and Mauvesin Barton. “We use a range of services and we also have rain radars that help us predict the very near-term weather. They are the same as the ones they use at Rolland Garros [France’s major tennis tournament].”
Bréhant uses several sustainable agricultural practices too, avoiding any particular certification in a bid to stay open to all possibilities. Plus, it means his team knows how to work with all the available options. Bréhant’s approach to mildew is twofold. About 20% of the vineyard is treated only with sulphur and as little copper as possible. “On the other 80%, we use a mix of treatments, including synthetic chemicals as needed.”
In a clear example of what softer options mean in terms of time and labour, in 2018, one of Bordeaux’s worst mildew years, Bréhant said he used 16 copper applications on the non-synthetic chemical area. On the other 80% he used four copper and five synthetic treatments. Remarkably, there was no loss of volume, thanks both to the work they put in, rising early, finishing late, Sundays included, and the fact their soils have less clay. That means they hold less water, which reduces the general humidity and fungal growth liability.
In Champagne, weather data is gathered via 45 automatic weather stations which send data to the CIVC, which in turn relays it to producers. A grading system for sprayers is also being developed which should be ready by year-end and will help growers choose the best and most environmentally friendly sprayer.
Happily, highly targeted treatments are better for both the environment and controlling fungi. One of the newer developments here, says Descôtes, are sprayer collection panels. That means less air pollution and less waste, as the drops collect on panels attached to sprayers and are reused. The downside is that it takes about twice the time to spray the vines.
Equipment itself must be in good condition. Sprayers have to be tested every year, well ahead of the mildew risk period. In terms of how many sprayers are needed, Bernos says the general rule is every estate should have enough material and people to treat the entire vineyard in one day. He notes that one of the problems in 2018 was that people were trying to do everything in half a day, due to the rain’s frequency.
Other levers vintners use to control fungal infections are leaf density and surface area. At its most basic, that means removing leaves to increase fresh air and sunlight around the vines. This is especially important for botrytis control, where prevention is the principal cure. Because sun powers vine growth, the leaf canopy must also be managed carefully. “You want some sun on the leaves, but again you want to control the sun’s power by getting the right amount of shade to optimise the lighted leaf surface,” says Barton’s Bréhant.
Leaf density control starts early in the growth cycle, he adds, by controlling fertiliser dosage. Bréhant, who makes his own compost, says he uses it judiciously. “We don’t want to overpower the vines,” and produce too much foliage.
To achieve the ideal leaf surface area, Bréhant uses traditional Medoc knives called “fauchon”. The trimmers walk between the vines, swinging knives in both hands. “It’s very precise and much more environmentally friendly than a tractor with a mechanical trimmer,” he says. The risk of plant or grape damage is lower too. Again, however, it is much slower than a tractor.
Looking ahead, the CIVB’s Charlier sees winemakers becoming ever more technical and reactive as they gain confidence and experience in a world where the most effective treatments are no longer the ideal ones.
To help them, Charlier believes they will have better materials and more training. “We know we are using slightly less effective products and we know that is a risk. But it is for a good reason,” he said.
As to copper itself, the real debate is perhaps only beginning.
