Weeds are growing resistant to the herbicides already on the market, and agribusiness companies like Bayer are in a desperate search for new modes of action to help farmers kill them.

Bayer’s Icafolin product will be its first new mode of action herbicide in some 30 years when it launches in Brazil in 2028.

Frank Terhorst, executive vice president of strategy and sustainability at Bayer’s Crop Science Division, told Reuters on Monday that AI could help speed up finding that next new mode of action.

“You want to find the one where you have maximum performance on what you want to kill – weeds, and basically no impact on everything else. And that balance is extremely difficult,” Terhorst told Reuters after an event in Chicago.

AI, he said, helps the company match the protein structure of a weed with a molecule that targets that structure, and enables it to use huge amounts of data.

It is a faster process, he said, and there are fewer dropouts.

Bob Reiter, head of research and development, crop science, at Bayer, said in a statement that with AI tools, the timeline for the discovery of the next new mode of action could be much shorter.

“If we take the example of early research only, we today have at least three times the number of new modes of action compared to ten years ago,” he said.

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In many cases weeds are developing resistance against multiple herbicides, scientists said.

Reuters interviewed two dozen farmers, scientists, weed specialists and company executives and reviewed eight academic papers published since 2021 which described how kochia, waterhemp, giant ragweed and other weeds are squeezing out crops in North Dakota, Iowa, Wisconsin and Minnesota as chemicals lose their effectiveness.

Over the last two decades, chemical companies have reduced the share of revenue devoted to research and development spending and are introducing fewer products, according to AgbioInvestor, a UK-based firm that analyzes the crop protection sector.

Farmers say their losing battle with weeds threatens grain and oilseed harvests at a time when growers are grappling with inflation and extreme weather linked to climate change.

“We’re in for big problems over the next 10 years for sure,” said Ian Heap, director of the International Survey of Herbicide Resistant Weeds, a group of scientists in over 80 countries that maintains a global database. “We are in for a real shake-up.”

The database records reduced effectiveness for glyphosate, one of the most common herbicides, against 361 weed species, including 180 in the U.S., affecting corn, soy, sugar beets and other crops.

Some 21 weed species globally showed resistance to dicamba, the most recent major U.S. chemical, which launched in 2017.

Environmental groups argue that farmers should embrace natural weed-control methods instead of chemicals.

Kochia, which spreads as many as 30,000 seeds per plant, can cut yields by up to 70 per cent if left unchecked, according to Take Action, a farmer resource program of the United Soybean Board.

Other factors, including the development of more robust seeds, have pushed overall global crop yields higher. But scientists expect weed problems to worsen, with some weeds showing resistance to chemicals even on first exposure.

‘Really scary’

In Douglas, North Dakota, farmer Bob Finken sprayed dicamba and glyphosate to kill late-season weeds. Neither product eliminated kochia.

“That was really scary,” said Finken, 64. “Each year seems to get a little worse.”

Finken was forced to clear the weeds with harvesting equipment, which risks clogging expensive machinery.

Other farmers are hiring workers to pull weeds by hand, said Sarah Lovas, an agronomist with GK Technology, a precision agriculture firm.

North Dakota was the largest spring wheat producing state in 2023 and ninth-biggest soybean grower.

Five of North Dakota’s 53 counties have confirmed populations of dicamba-resistant kochia, a year after it was first reported in the state, North Dakota State University weed specialist Joe Ikley said.

“It’s just a matter of time before it hits your farm,” said Monte Peterson, 65, who grows soybeans near Valley City, North Dakota.

Lab scale-back

Chemical producers Bayer, Corteva and FMC FMC.N say longer development and regulatory processes have constrained new products to combat weed resistance. Industry executives say regulators have become more stringent about environmental and health impacts.

The U.S. Environmental Protection Agency (EPA) said standards for approving new herbicides have not substantially changed since 1996. However, the EPA said recent efforts to assess the impact of new active ingredients on threatened plants and wildlife have delayed some decisions.

The EPA did not estimate the increased processing time. The agency said it expedites reviews of lower-risk products.

Farm chemical companies spent 6.2 per cent of sales revenue on development of new active ingredients in 2020, down from 8.9 per cent in 2000, AgbioInvestor said. Its data showed the introduction of new active ingredients fell by more than half in 2022 from 2000.

Instead, companies have expanded uses of existing products like dicamba, glufosinate and 2,4-D.

FMC plans the 2026 launch of an herbicide to kill grassy weeds in rice crops based on the industry’s first new mode of action, a term for the way a chemical kills a weed, in three decades.

The herbicide was in development for 11 years. FMC hopes it will generate $400 million in sales within a decade, a fraction of the roughly $8 billion global glyphosate market.

“If we don’t keep developing the new products, we are going to run into a wall where growers don’t have the tools to combat the pests,” CEO Mark Douglas said. “And then ultimately you face food security issues.”

The world’s biggest agriculture chemical and seed company, Germany’s Bayer, hopes to produce its first new mode of action herbicide in over 30 years by 2028.

“We’re really desperate for (new modes of action) if we’re going to sustain uses for farmers,” said Bob Reiter, head of research and development for Bayer’s crop science division.

Two decades ago, companies commercialized a product for every 50,000 candidates, but it now takes 100,000 to 150,000 attempts, Reiter said.

U.S.-based Corteva said it has incorporated sustainability criteria, such as reduced groundwater risk, in its research and development, aiming to clear the path with regulators.

It hopes that approach will shorten the regulatory process when it introduces a fungicide with a new mode of action against Asian soybean rust disease in Brazil around 2027, said Ramnath Subramanian, vice-president of crop protection research and development. He did not say how much shorter the process may be.

Bill Freese, scientific director of the Center for Food Safety in Washington, said farmers should shift away from crops genetically engineered to tolerate herbicides, which lead to plants becoming resistant to multiple chemicals through repeated sprayings.

“It’s like this toxic spiral,” Freese said. “There’s no end in sight.”

–Reporting for Reuters by Rod Nickel in Winnipeg, Manitoba and Tom Polansek in Chicago.

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Writing Monday in the ag ministry’s Field Crop News, Ontario provincial weed management specialist Mike Cowbrough said the plant in question, found in Wellington County, is confirmed as palmer amaranth.

The species has previously been dubbed the most troublesome weed in U.S. agriculture, but hasn’t yet appeared in Canada in a significant way; its only other recent known appearance in Canada outside Ontario was by a couple of plants in a southern Manitoba bean field in 2021.

While the broadleaf weed is known for its physical height — up to eight feet — and aggressive rate of spread, it’s also infamous in the U.S. and elsewhere for its adaptability against herbicides, making it even more difficult to keep in check.

The International Herbicide-Resistant Weed Database has logged cases in multiple countries of palmer amaranth plants showing resistance to one, two or three herbicide modes of action, along with two cases in the U.S. — Kansas in 2015 and Arkansas in 2016 — where the plants were resistant to five modes.

The database also documents one case, in a Kansas sorghum field in 2021, in which a palmer amaranth plant showed resistance to six different herbicide modes of action (groups 2, 5, 6, 9, 14 and 27).

In all, populations of palmer amaranth have been found with resistance to one or more of nine different modes.

Cowbrough, in his post Monday, said “it was only a matter of time” before the weed turned up in Ontario, as it was already in the Ontario-adjacent states of New York and Michigan — and has been seen in all other states bordering the Great Lakes.

Provincial specialists had also previously confirmed one-off appearances in separate spots in Ontario in 1966, 1978 and, most recently, in 2007 near Niagara Falls.

“The most valuable thing that can be done at this point is to know the process to identify any plants you suspect may be palmer amaranth and destroy any plants before they produce seed,” Cowbrough wrote.

But proper identification may be a tall order; Ontario weed specialists have previously noted it’s extremely difficult to discern palmer amaranth — or its relative, waterhemp, for that matter — from other pigweed species, especially when spotted as seedlings.

For example: the Wellington County landowner who called in the newest case described it as “‘a weird looking pigweed’ that just looked different than anything they had seen before,” Cowbrough said.

However, he said, that goes to show farmers’ gut instinct is “usually a pretty good screening tool for when you should seek help” confirming either palmer amaranth or waterhemp.

Early detection, particularly when the number of plants involved is small and manageable, is important, he said. Any palmer amaranth plants could be pulled or dug out, roots included, to prevent any seed from being produced and/or dispersed.

To help prevent the weed from gaining a toehold, Cowbrough said fall-seeded crops such as winter cereals and winter canola can “create an environment that is not ideal for (weed) seed germination.” Cover crops planted after a crop harvest are also known to generally help reduce pigweed populations that germinate and can produce viable seed.

Perennial forages such as alfalfa, he said, offer “the best opportunity” to prevent seedlings from germinating — and to draw down the weed population’s seed bank through “predation and other environmental stressors.”

For fields that are going into corn and/or soybean, finding an effective pre-emergence herbicide is “extremely important,” he said, as it would take out a “significant amount” of a first flush of palmer amaranth seedlings and make sure there’s not a “huge range” in weed stage for any post-emergent spraying that follows. — Glacier FarmMedia Network

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At the Ag in Motion outdoor farm show this week, field residue management manufacturer Redekop won the Innovations Award for Environmental Sustainability for its harvest Seed Control Unit, which destroys more than 95 per cent of unwanted seeds the combine leaves behind.

With different weeds and weed varieties becoming increasingly resistant to glyphosate herbicides, integrated weed management will be vital for western Canadian farmers in the near future.

Redekop field support and salesperson Neale Heinrich was at the Discovery Farm for this year’s Ag in Motion event, coming from Australia. The battle with herbicide-resistant weeds Down Under has spanned decades, particularly against Italian ryegrass.

“We’re close to 40 years of resistance, building and building,” said Heinrich.

“It’s been a battle. All sorts of different processors, chaff carts, burning, all sorts of stuff.”

There are many different ways to control weed seeds at harvest, such as chaff-collecting, chaff-trampling, chaff-lining, baling behind the combine and burning the straw.

Some methods remove the chaff, and in turn remove most of the seeds with it. Chaff-trampling and chaff-lining concentrate the chaff into lines, which create rot and make it difficult for the weeds to grow while reducing their spread.

The Redekop Seed Control Unit destroys the seeds that leave the combine through the chaff and spreads a refined dust across the field, removing the seed problem without removing the straw.

Managing the chaff is key to eliminating herbicide-resistant weeds because they are typically spread through the combine’s straw chopper, broadcasting the seeds across the field.

Breanne Tidemann, a research scientist at Agriculture and Agri-Food Canada, wants to find ways to limit how many weed seeds remain in the field after harvest, and in turn limit weed growth and reproduction.

“When we’re applying herbicides, we’re trying to stop those seedling stages,” she said.

“we’re focusing on that part of the life-cycle — let’s kill those seedlings. But those seedlings we don’t manage to kill, those that return, the ones that produce the seeds that we’re broadcasting, those that are a problem in the current system, they’re probably the most herbicide-resistant.

“They’re the ones that have avoided every other thing that we’ve thrown at them so far, and they’re going to come back and grow again next year. We’re making our lives harder by putting those back into our soil.”

Tidemann specializes in integrated weed management, weed biology, harvest weed-seed control and managing herbicide-resistant weeds. She spoke at Ag in Motion Tuesday on herbicide-resistant weeds in Western Canada and how to manage them.

Wild oats, kochia, cleavers and green and yellow foxtail are some of the many weeds becoming resistant to herbicides across the Prairies.

Tidemann’s research shows that 74 per cent of any weed that is put through the harvester will be herbicide-resistant, and so will their seeds.

“Three out of four fields that have weeds in them around harvest time probably have resistant weeds,” said Tidemann.

The number is also increasingly rapidly. Her studies show that kochia in Alberta was first observed as being glyphosate-resistant in 2011, and in 2012 five per cent of populations were resistant.

In the most recent 2021 survey, 78 per cent of kochia in Alberta is resistant. The resistance is growing in population and in strength, making more herbicides useless against them.

For Heinrich, this sounded all too familiar.

“Listening to Breanne (Tidemann), you want to get on it,” he said.

“If you can learn anything from Australia’s perspective, we’re fighting, we’re fighting back and working our hardest to try to get ahead of it, but it’s been ahead of us.”

Taking the seeds out of the field helps Australian farmers regain control of their farmland, although Heinrich said it took them a long time for the seed banks to empty.

Newcomers to integrated seed management can’t expect weeds to leave the field instantly, although they can expect to see their weeds stay more concentrated rather than spread across the field.

“It’s a long-term (plan),” said Heinrich. “We do have clients that have said they’ve taken on a piece of property and it was filthy with weeds when they took it, then the following year they came back to harvest and they’ve seen a marked difference.”

While integrated weed management has been widely adopted in Australia, it has not gained a lot of traction in Western Canada. Tidemann said only 20 to 30 Redekop Seed Control Units are being used across the Prairies.

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Harvest weed seed control might not be a golden bullet to tackle glyphosate-, fluroxypyr- and dicamba-resistant weeds, but according to Agriculture and Agri-Food Canada researcher Breanne Tidemann, it’s part of the range of solutions needed to stem the tide.

“You’re not going to spray your way out of this,” Tidemann said about herbicide resistance during her presentation at Ag in Motion.

“If you get a new product or new mode of action that works really well, everyone is going to adopt it, the selection pressure is going to go through the roof and we’re going to break that next tool, too. So, continuing to hope, cross our fingers, wishing and praying a new product is going to come out and save us is a little bit naïve, a little wishful thinking.”

However, the ability to mechanically separate weed seed at the point of harvest is part of the diversification solution that looks beyond just chemicals.

Development of harvest weed seed control started in the early 2000s in Australia before moving onto commercialization with the Harrington Seed Destructor trailer unit.

There are limitations to the implement, mainly that the weeds need to be either tall or short enough to fit in the header. However, once they do, the weed seeds are largely ground up into a flour-like material, doesn’t broadcast and can be an effective tool in not only limiting spread but getting to the core of the issue. As long as weeds are harvested, seed destructors have a more than 95 per cent rate of success.

Canadian research with the unit began in 2014, but since then, integrated harvest weed seed control implements for combines have been developed and are now commercially available.

While initial research is promising in demonstrating the implement will have significant impact on both weed control as well as limiting broadcast, weeds will likely be able to adapt even to mechanical attempts at tackling weeds.

“Weeds will adapt. Weeds are dirty little buggers that will find some way — they’ll mature more quickly, they’ll drop there seeds earlier, they’ll become more prostrate,” said Tidemann.

“We’ll see adaptations, I firmly believe that, particularly if we switch whole hog from only herbicides to only relying on this.”

She said it’s about redundancy, adding the solution is to use a range of techniques.

As far as where the technology goes next, Tidemann said the speed in which it’s already progressed is impressive and manufacturers of weed seed harvest control implements are continually improving the product.

“They are really listening to farmers,” she said.

“A farmer will say, ‘I had a problem with a metal bolt going through and it damaged my mill, I had to do a lot of repairs.’ The next thing you know, they’ve got a magnetic strip to catch metal pieces before they go through the mills.”

As development work continues, Tidemann said she hopes the technology is more widely adopted in Canada.

“My understanding from talking to colleagues (in Australia) is 80 to 90 per cent of their farmers are using some form of harvest weed control,” she said.

“Western Australia is showing it can be incorporated into a system and it can help and it can work.”

There is a cost, with units running in the $100,000 range, but Tidemann said it’s likely less than what farmers might think because it can be used on one combine that can tackle particularly weed patches rather than being required on every combine.

— Alex McCuaig reports for the Western Producer from Medicine Hat.

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Quebec’s Reseau d’avertissement phytosanitaire (RAP) last Friday reported a patch of waterhemp with resistance to mesotrione herbicide in the Haut-Richelieu municipality, in the province’s Monteregie.

A Group 27 HPPD enzyme inhibitor, mesotrione is the active ingredient in Syngenta’s Callisto herbicide and one of several in products such as Halex and Acuron, all used mainly for broadleaf weed control in corn crops.

Tests by the Centre de recherche sur les grains (CEROM) also confirmed resistance to Groups 2, 5 and 9 (atrazine, metribuzine and glyphosate respectively) in the same waterhemp patch, RAP reported.

Established in Ontario since 2002, Manitoba since 2016 and Quebec since 2017, having arrived via the central and eastern U.S., waterhemp is able to germinate all throughout a growing season.

The weed is also known to be highly prolific — a single plant can produce up to 300,000 seeds — and if left unchecked, has been known to cause yield losses of up to 73 per cent in infested corn and soy crops, RAP said.

The plant also grows rapidly, at a rate of up to 2.5 to three centimetres per day, and is tough to distinguish visually from relatives such as redroot and green pigweed.

Waterhemp patches in Ontario have previously shown resistance to groups 2, 5 and 9 and, more recently, Group 14. That group includes PPO inhibitors such as Syngenta’s Reflex and Corteva’s Goal, also used mainly for broadleaf weed control.

The Quebec agriculture ministry previously set up a support program to help corn and soy growers deal with waterhemp infestations. RAP, in its notice last Friday, urged affected producers to sign up for the program, to help limit the weed’s further spread in the province. — Glacier FarmMedia Network

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The weed grows very fast, reaching up to eight feet in height and can hold back commercial crops, potentially threatening hundreds of millions of dollars of production.

Yield losses have been reported of up to 91 per cent in corn and 79 per cent in soybeans, according to the U.S. Department of Agriculture (USDA), in areas where the weed has previously been found.

The weed is native to the dry, southwestern part of the U.S. In some parts of that region, it has developed resistance to glyphosate, the active ingredient in Monsanto’s Roundup and other herbicides.

The federal Conservation Reserve Program (CRP) pays farmers to return tilled acreage to native plants. The Minnesota investigation is seeking to determine if the program inadvertently introduced the weed into the state.

Palmer amaranth also has appeared in Iowa, Illinois, Indiana, Ohio, Nebraska, Wisconsin and Michigan, including on land in the federal conservation program. Growers and weed experts on the Canadian Prairies and in border states such as North Dakota are also watching the weed’s northward progress into the Plains region.

Minnesota tracked down the weed on the conservation areas in the southwestern part of the state, after the person who created the seed mix and planted it said that the plots might be contaminated. He had been alerted by a client who had spotted the weed on conservation land, according to state agriculture department spokesman Allen Sommerfeld.

Minnesota now wants to find out where the weed seed came from and how it got into the conservation mix, according to University of Minnesota professor and extension weed scientist Jeff Gunsolus, a researcher involved in the investigation.

Under the state’s seed law, it is illegal to sell or transport seed mixes containing the Palmer amaranth seed. Penalties can include fines of up to $7,500 per day, Sommerfeld said (all figures US$).

Investigators are interviewing individuals, including some at seed companies, as well as analyzing seeds and mixes, and checking the accuracy of seed labels, said Clifford Watrin, a supervisor of seed law at the state’s agriculture department.

Last week, Watrin told native seed suppliers and planters in a letter that extra monitoring of seed supply was needed. The agriculture department now has a DNA test for Palmer amaranth seeds, as the seed cannot be distinguished from other weed seeds by sight. Agriculture officials hope this test will help stop more Palmer amaranth seeds from entering the local market.

Minnesota has set aside $50,000 for the investigation, said Watrin. Governor Mark Dayton has called for another $300,000 a year to boost resources for enforcing state regulation over weeds, Sommerfeld said.

Though Palmer amaranth has also appeared in conservation plantings in other states, it has been hard to narrow down the source.

Farmers of commercial crops have been keen to sign up for the federal conservation program to supplement incomes as grain prices fall. USDA said Tuesday it expects net farm income to fall in 2017 to its lowest level since 2002.

USDA told Reuters it was aware of the problem present in seed mixes, but does not monitor seed lots purchased by participants.

— Renita D. Young is a multimedia journalist covering commodities for Reuters in Chicago. Includes files from AGCanada.com Network staff.

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While approval had been expected, it is seen as a major step forward for the company’s newest herbicide tolerant products amid rising problems in the U.S. farm belt with weeds resistant to glyphosate, the main ingredient in Monsanto’s Roundup weed killer.

Environmental groups criticized the EPA approval.

The Center for Biological Diversity said the ruling would lead to sharp increases in pesticide use that could harm threatened plant and animal species, including the whooping crane.

“Piling on more pesticides will just result in superweeds resistant to more pesticides,” said Nathan Donley, a scientist with the group.

The EPA signed off on Monsanto’s XtendiMax herbicide for in-crop use on Roundup Ready 2 Xtend biotech soybeans, designed to tolerate applications of glyphosate and dicamba, and its Bollgard II XtendFlex cotton, which can tolerate the two chemicals as well as glufosinate.

The company is still awaiting an EPA ruling on its Roundup Xtend herbicide, a glyphosate and dicamba blend.

Farmers have used dicamba for years to kill weeds ahead of planting, but until now have not been allowed to use it on growing crops.

Monsanto has invested more than $1 billion in a dicamba production facility in Luling, Louisiana, to supply demand it expects will blossom in the coming years. The company has said the Xtend platform will be its largest-ever technology launch.

The company said it expects the soybean variety to be planted on 15 million U.S. acres in 2017 and its cotton to be planted on more than 3 million acres.

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Any weeds that lived through pre-seeding burnoff or post-emergent spraying — where other weeds have clearly died — are best caught early, the Canola Council of Canada said in a release Friday.

“It takes 14-21 days after a pre-seed glyphosate application for glyphosate-resistant kochia to become obvious, so keep an eye out while crossing over the farm while seeding or during in-crop herbicide applications,” council agronomy specialist Angela Brackenreed said.

The International Survey of Herbicide Resistant Weeds now documents 21 different weeds on Canada’s Prairies with herbicide resistance, mostly to Group 1 or Group 2 herbicides and in some cases to multiple groups, the council said.

As of February, there are 61 confirmed and unique cases of herbicide-resistant weeds across Canada, behind only the U.S. (150) and Australia (75), according to the ISHR.

Hugh Beckie, a research scientist with Agriculture and Agri-Food Canada in Saskatoon, estimated the number of acres on the Prairies with at least one resistant weed has gone from 10.9 million in the early 2000s to 38 million last year.

Beckie’s research also shows cleavers is one of the next most likely weeds to develop resistance to glyphosate (Group 9), the council said.

“Without management, these weeds will continue to spread and the effect on grower profits will only get worse,” Beckie said in the council’s release.

Growers also shouldn’t expect new herbicide modes of action to come along as they did 20 years ago, BASF rep Andrew Reid of Lacombe, Alta. said in a recent essay, noting the last such mode launched in the Prairie market was Group 27.

All that said, Brackenreed added, “we don’t want growers to throw up their hands and give up. This is a manageable situation.”

Growers, she said, should watch out for weed patches and any performance issues that raise suspicion, then mark those spots and use various tools to contain those patches “or, ideally, remove them entirely.”

The council urged a combination of early weed control, rotation of herbicide groups, crop rotation, tank mixes and pre-harvest or fall spraying where feasible.

The council also recommends closely following herbicides’ label directions on timing, specific controlled weeds and correct rates. Cutting rates, the council said, “may reduce herbicide efficacy and increase weed seed return to the soil seed bank.”

Brackenreed, who’s based at Minnedosa, Man., also recommended farmers follow integrated weed management (IWM) practices at seeding, such as higher seeding rates, shallow seeding depth and narrow row spacing among other tools to boost crop competitiveness.

“These techniques reduce the reliance on herbicides, which will actually improve results from herbicides and keep more herbicides working on the farm,” she said.

Tillage at pre-seed or post-harvest, to help manage emerged weeds or to encourage weed germination for winterkill or chemical control, is also an effective mechanical option if used properly, Reid said. Spot mowing, to prevent seed set, is another such option, the council added. — AGCanada.com Network

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The U.S. Environmental Protection Agency (EPA) confirmed it will require a weed resistance management plan for glyphosate, the key ingredient in Monsanto’s immensely popular Roundup herbicide.

The agency has scheduled a conference call for next week with a committee of the Weed Science Society of America to discuss what the final plan for glyphosate should entail, said Larry Steckel, a Tennessee scientist who chairs the committee.

An EPA spokeswoman declined to give specifics of the plan, but told Reuters that its requirements will be similar to those placed on a new herbicide product developed by Dow AgroSciences, a unit of Dow Chemical.

Requirements for the Dow herbicide include weed monitoring, farmer education and remediation plans. The company is required to provide extensive reporting to the EPA about instances of weed resistance and to let “relevant stakeholders” know about the difficulties of controlling them via a company-established website.

Monsanto spokeswoman Charla Lord would not discuss whether the company was negotiating a plan with regulators, but said Monsanto “will continue to work with the EPA to ensure proper product stewardship as we move through the regulatory process.”

At least 14 weed species and biotypes in the U.S. have developed glyphosate resistance, affecting more than 60 million acres of U.S. farmland, according to data gathered by the U.S. Department of Agriculture and U.S. weed scientists. The herbicide-resistant weeds hinder crop production and make farming more difficult and expensive.

The EPA’s action comes in the wake of a finding by the World Health Organization’s cancer research unit this month that glyphosate is “probably carcinogenic to humans,” a conclusion the working group said was based on a review of years of scientific research. Testing has found residues of the herbicide in water, food, urine and breast milk.

The EPA’s weed management plan will not address human health concerns, but the agency is also analyzing health data as part of a required reevaluation of the herbicide.

The EPA’s preliminary risk assessment of glyphosate is expected to be released for public comment later this year, and the agency will publish its proposed weed management plan for public comment at the same time.

Regulators in the U.S. and many other countries have long considered glyphosate among the safest herbicides in use. A review of the chemical by the German government for the European Union last year concluded that no link to cancer has been established.

And Monsanto, which held the patent on glyphosate until 2000 and last year sold more than US$5 billion of Roundup herbicide, says the weed-killing agent has been proven safe repeatedly. Last week, the company blamed “agenda-driven groups” for fuelling false reports about glyphosate.

But the chemical’s critics, including environmentalists, scientists and opponents of genetically modified foods, hope the WHO finding will help convince the EPA that tighter controls on the herbicide are needed, not just to prevent the growth of herbicide-resistant weeds, but also to protect human health.

On March 26, a coalition of public interest groups, including the Natural Resources Defense Council, and the Center for Food Safety sent a letter to EPA administrator Gina McCarthy urging the agency to “weigh heavily” WHO’s finding as it prepares its risk assessment.

Huge ramifications

How the EPA chooses to handle glyphosate is a closely watched issue for the agricultural industry.

Globally, the herbicide is a key ingredient in more than 700 products and is used to control weeds in gardens, along roadsides and on millions of acres of farmland.

Steckel said his committee will express some concerns in its call with the EPA next week. Specifically, he said, the group sees shortcomings in the management plant the agency has for Dow AgroSciences and would like a glyphosate plan that allows for state-specific provisions.

“We are here on the ground, and we think we could tailor things to have more impact than just one overarching plan from the federal government…,” said Steckel, a row crop weed specialist at the University of Tennessee. “We have to preserve these herbicides. There really are no new ones.”

At least 283.5 million pounds of glyphosate were used in U.S. agriculture in 2012, the most recent year for which data is available, up from 110 million pounds in 2002, according to the U.S. Geological Survey.

According to the U.S. Department of Agriculture, more than 90 per cent of the soybeans and cotton grown in the U.S. last year, and 89 per cent of the corn, was genetically modified to withstand herbicide applications.

–– Carey Gillam is a Reuters correspondent covering agriculture and agribusiness from Kansas City.

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