The glyphosate dilemma

It’s only a small molecule. It’s cheap. It’s widely used. And it’s rapidly becoming the most contentious topic in the world of wine. But if its use in viticulture is banned, as many are advocating, it could cause seismic changes and push the price of wine up to levels that would cause a large drop in consumption. 

It is the herbicide glyphosate, widely known by one of its trade names, Roundup. Eight hundred million tonnes of this chemical – an amino acid with a chemical group called a phosphonate attached – are used each year to kill weeds. And viticulture is hooked on the stuff.

A new tool

Glyphosate didn’t start life as a herbicide. In 1964, Stauffer Chemical patented it for use in de-scaling industrial pipes. In 1970, Monsanto chemist John Franz found it to be an effective broad-spectrum herbicide, and in 1974 it was registered for this use. Monsanto had hit the jackpot. Here was a herbicide that was not only cheap and effective, but apparently safe: it targets a series of chemical reactions called the shikimate pathway, critical for the function of plants and some microbes but absent in humans. 

Initially, glyphosate was used to eliminate weeds before sowing crops. But then someone discovered microbes that had developed glyphosate resistance: scientists took these genes and introduced them into soybeans (1996) and later maize, alfalfa, sugar beets, cotton and canola. This genetic modification made so-called Roundup Ready crop plants resistant to the herbicide, so glyphosate could be used to eliminate weeds all through the growing season; 90% of soy, corn and cotton now grown in the USA is genetically modified to be glyphosate-tolerant. The herbicide is also a desiccant and, just before harvest, crops are treated with glyphosate to kill the green tissues and accelerate drying. This desiccation, also known as siccation, results in increased yields of cereals. It also leaves glyphosate residues on the seeds. 

The success of glyphosate has been nothing short of astonishing. It is the most widely used herbicide worldwide. It’s estimated that enough is applied each year for every hectare of crop land on the planet to receive half a kilogram. Monsanto’s patent expired in 2000, and now about 50% of the glyphosate sold is made by other manufacturers (Monsanto is now part of Bayer and its formulation is sold under the trade name Roundup). 

Glyphosate is widely used in vineyards worldwide. It offers a relatively low-cost method of killing weeds which grow under vines and can compete for water and other resources, lowering yields and which, if left, can grow into the canopy itself. In contrast, manual control requires specialist equipment, is expensive, and raises the carbon footprint of viticulture. 

The controversy

This prevalent but previously low-key herbicide became somewhat of a household name four years ago when its safety, one of its selling points, came under question. In 2015, the World Health Organization’s International Agency for Research on Cancer classified glyphosate as “probably carcinogenic”. In the USA, Bayer has been fighting court cases from plaintiffs including groundskeeper Dewayne Lee Johnson, who developed non-Hodgkin’s lymphoma after working with Roundup on a daily basis. An initial trial found in Johnson’s favour in 2018, and a number of other court cases have begun. In 2017, French President Emmanuel Macron pledged to ban glyphosate in his country within three years, but later backtracked because of opposition from farming lobbies. 

“Most vineyards worldwide use some sort of herbicide,” says Dr Mark Krasnow, a viticultural consultant working in New Zealand, “with glyphosate being one of the most common due to its systemic nature and low cost.” But is it a problem? “All herbicides can have unintended consequences on non-target organisms, and we don’t understand enough to really answer that question, especially in respect to its effects on the microbial communities in the soil. In terms of human health effects, I think the problem with glyphosate is more of a perception problem than an actual high risk.” This view is echoed by the Australian Pesticides and Veterinary Medicines Authority, which has assessed glyphosate and found no grounds to ban its use. The APVMA’s position is that approved products containing glyphosate can continue to be used safely according to label directions.

Mimi Casteel, of Hope Well Wine and Vineyard in Oregon, has become a vocal critic of glyphosate. Her issue is that it ends up in the soil and because of its chelating ability – its tendency to bind to other molecules – can interfere with plant nutrient uptake. “It is well documented in the literature that in field settings, between 20% and 60% of glyphosate applied in strip or broadcast applications ends up in the soil by virtue of the canopy of the weed stand not being impermeable and therefore allowing for the droplets to reach the ground,” says Casteel. “And in controlled experiments, up to 20% of glyphosate applied to plants is released into the soil via root exudate. Lastly, when plants die, as there is no breakdown of glyphosate in vivo in the plant, the residues are released to the soil through the degradation pathway.” But even when glyphosate is degraded, the breakdown product, aminomethylphosphonicacid (AMPA) is itself a powerful chelator. Together, both glyphosate and AMPA affect soil nutrients through chelation of micronutrients, and also affect the microbial life in the soil.

Casteel says glyphosate is a potent chelator of such elements as magnesium and calcium, “both of which are critical for formation of robust tissues during flowering and veraison [ripening],” she says. It makes trace minerals, important for critical enzymatic pathways that drive metabolism, less available. “Major metabolic pathways are dampened or completely stopped when you pull one or more of the cogs out of the machine,” says Casteel. “Glyphosate is known to inhibit more than 250 enzymes, including several that are critical for repairing DNA damage.” 

Nigel Sowman, viticulturist with Dog Point in New Zealand’s Marlborough wine region, thinks that glyphosate can increase disease problems. “Plant roots will take up a lot of what’s in the soil solution, meaning that glyphosate or its derivatives are entering the plant in sub-lethal doses,” he explains. “Like anything, constant sub-lethal doses can build up.” On his organically farmed vineyard, botrytis is much less of a problem. “What I have seen over some very challenging years is very little bunch-to-bunch transfer of botrytis: every plant has a small amount but it doesn’t go rampant. Much like a vaccination, a small amount of botrytis triggers an immune response, protecting the rest of the plant. But with sub-lethal doses of glyphosate, this immune response is compromised and botrytis spreads quickly in the late season.”

Uses and abuses

Bayer, which now owns Monsanto, disagrees about some of these assertions. “One of its biggest assets is that it is non-persistent,” says Dr Julian Little, head of communications and government affairs for Bayer’s crop science division in the UK. “It doesn’t hang around long and is rapidly broken down by microbes.” He admits that it does act as a chelator. “But the fact that it doesn’t hang around long means that it is a relatively short-term chelation that is minor and short-lived.” Little says it is extremely unlikely that there would be enough glyphosate in the soil for it to have much effect on the vine.

But one indisputable problem with glyphosate use is the development of resistant weeds.“We have already had resistance to multiple herbicides evolve in ryegrass in New Zealand, including to glyphosate,” says Krasnow. “If we continue to use herbicides, more weeds – and more challenging weeds – will develop resistance, as has happened overseas.” He adds that the recent court decisions in the US have further damaged glyphosate’s reputation with consumers, and “the writing is on the wall that it will not be a tool in the grower’s toolbox for too much longer. Either resistant weeds, or more likely, resistant consumers, will mean we have to abandon its use.” He says that while it’s possible to grow high-quality grapes without herbicides, it’s expensive and yields are lower. “Some growers could potentially be unable to cope with the reduced yields and could lose their vineyards.”

It’s entirely likely that a glyphosate ban could result in more expensive wine, and consequently reduced demand, causing a contraction in the global vineyard. To enforce this ban, which would likely have severe unintended consequences for many winegrowers, would seem a little premature because the science isn’t yet fully clear. Dr Little says that Bayer is concerned because any such decisions need to be evidence-based. “We are shifting into this post-scientific phase of deciding what is and what isn’t safe,” he says. “You are heading straight down the line of the anti-vaccine movement. Science is no longer seen as a valid currency for making decisions.”

Biodynamic South African winegrower Johan Reyneke says that while he’s not a fan of glyphosate, “one has to take context into consideration. Sustainability is a three-legged chair: nature, people and money. If the money leg goes, the chair falls over immediately, but people and nature can be exploited longer.” He continues, “so I’m saying there has to be a drive to look after nature and people better, but if the drive is too harsh, money goes and the whole chair falls over immediately.”

This is clearly an area where there will be continued controversy. “As the self-proclaimed leader of progressive agriculture, viticulture has some soul searching to do,” says Hope Well Vineyard’s Casteel. “There is a very wide hole in those claims when glyphosate is part of a sustainability program, because the assertion that glyphosate use in vineyards is ‘benign’ weed control that protects vineyards from invasive weeds and eliminates tractor passes has no credibility.” She adds: “This is an epidemic that gets to the heart of what is fundamentally broken in agriculture. As it clings to its chemical weed control, viticulture is participating wilfully.”

Jamie Goode

This article was first published in Issue 6, 2019 of Meininger's Wine Business International magazine, available online or in print by subscription.