Busting 3 Common Myths About Weed Resistance
Weed control has always been a critical challenge for farmers, and herbicides are an important weed control tool. However, changes can occur in response to herbicide use and other management decisions. Changes in weed populations begin when a small number of plants within a species, called a "biotype," have a distinct genetic makeup that allows them to tolerate a particular herbicide application. Multiple weed biotypes can exist in a single field.
This myth-busting list debunks three common misconceptions about herbicide resistance.
MYTH 1: Overuse of glyphosate causes weed resistance.
BUSTED: According to the Weed Science Society of America (WSSA), the first reports of weed resistance occurred back in the 1950s. To date, there has been no evidence of glyphosate (or any other active ingredient) causing herbicide-induced mutation in any plant species. That is to say herbicides did not and do not cause resistance. Herbicide resistance is actually the plant's naturally inherited ability to survive and reproduce after exposure to what is considered to be a lethal dose of chemicals.
As a farmer continues to use a particular herbicide without any other herbicide modes of action, or doesn't use any other cultural practices (tillage, crop rotation, etc.), the resistant biotypes continues to survive and produce seed. Subsequent populations of the resistant biotype will continue to increase until they are the dominant weed in the field.
Common factors that are often present in areas where glyphosate resistance has developed are:
• Limited or no crop rotation
• Limited or no tillage practices
• Use of glyphosate alone or limited use of other actives
• Reduced or “cut” rates of glyphosate
Particular weed characteristics that can facilitate development of herbicide resistance include:
• Large amount of seeds produced per plant
• High level of germination of those seeds
• Several weed flushes per season
• High frequency of resistant genes
The best way to keep glyphosate powerful is to use it effectively. That mean including an effective tank-mix partner once per growing season and using a diverse crop rotation on your farm.
MYTH 2: Harsh residual chemicals are being used to control glyphosate resistant weeds.
BUSTED: All herbicides have to undergo the same testing and must meet the same health, safety and environmental standards.
Many farmers have grown accustomed to the convenience and effectiveness of using glyphosate alone. The best way to preserve its long-term effectiveness on weeds is to bring in other herbicide modes of action to support it. These complementary herbicides used with glyphosate are not “harsher”; they simply interact with the target weeds differently. They have met the same regulatory standards and have been through the same thorough health, safety and environmental evaluations as glyphosate.
MYTH 3: Herbicides are the solution to all our weed control problems.
BUSTED: Spraying alone is not enough – experts agree that herbicides are important, but other practices should also be implemented.
A successful Integrated Weed Management strategy includes agronomic best practices to limit the introduction and spread of weeds, including:
• Crop rotations
• Periodic tillage
• Seeding rates to promote crop competition
• Planting certified seed
• Cleaning equipment to minimize spread of weeds
Benefits of residuals:
Tank mixing with a herbicide that offers lasting residual effects is an added benefit of keeping fields cleaner, longer. Products like Monsanto’s Roundup Ready 2 Xtend™ soybeans are tolerant to both glyphosate and dicamba, allowing for the use of multiple modes of action and residual weed control.
Herbicides by the numbers
• Herbicide modes of action found to date: 20
• Most recent discovery of new herbicide: 80’s
• Anticipated time until discovery of new herbicide: 10+ years
Weed Science Society of America. Weed Myths. (verified 04/12/14) http://wssa.net/
Ross, M. Childs, D. Herbicide Mode-of-Action Summary. Department of Botany and Plant Pathology. Purdue University Cooperative Extension Services. (verified 04/12/14)https://www.extension.purdue.edu/
No one that I've read who's been critical of Monsanto's profitable adventures selling both "Round-up Ready" seeds (soybean, corn, etc.), and glyphosate herbicide (Round-up), has ever implied that glyphosate on its own has created resistance in weeds. It's HOW it's used, and simple biology that's led to resistant weeds.
Developing commercial GMO "Round-up Ready" crops that can survive glyphosate allows farmers to blanket spray tens of millions of acres every season, vastly increasing the biological certainty of "a small number of plants within a species, called a "biotype," have a distinct genetic makeup that allows them to tolerate a particular herbicide". In other words it's the combination of the two (GMO seeds, and use of Round-up, both profit centres for Monsanto) that's created the problem. Rolling dice a hundred times and the chance of snake-eyes is slim. Roll them millions of times and the chances get much better.
Some of the most critical comments have come from scientists not worried about the use or safety of glyphosate, but that it's usefulness will disappear because of widespread use of Round-up Ready crops. That's on top of the growing concern about glyphosate's possible link to cancer.
There's lots to worry about and question when it comes to glyphosate, but this issue of weed resistance is the most serious legal and technical issue. Monsanto is very clear in its submissions to have Round-up Ready crops approved that resistance wouldn't be a problem. It is. If the cancer lawsuits weren't underway I suspect this would be the basis of more legal action.
Then there's the question of the newer herbicides needed to replace glyphosate. One is called dicamba. A recent article in the Washington Post reported that spray drift from dicamba onto crops that have no resistance is a serious and growing problem.
The genie is out of the bottle I know, but let's at least speak honestly about these things.
This miracle weed killer was supposed to save farms. Instead, it’s devastating them.
- August 29th, 2017
Lyle Hadden, a soybean farmer, walks through a field he's planted that shows signs of being affected by the herbicide dicamba. Photo by: Andrea Morales/For The Washington Post
Its leaves curl downward and in on themselves like tiny, broken umbrellas. It’s the telltale mark of inadvertent exposure to a controversial herbicide called dicamba.
“This is crazy. Crazy!” shouts Mayes, a farm manager, gesticulating toward the shriveled canopy off Highway 61. “I just think if this keeps going on . . .”
“Everything’ll be dead,” says Brian Smith, his passenger.
The damage here in northeast Arkansas and across the Midwest — sickly soybeans, trees and other crops — has become emblematic of a deepening crisis in American agriculture.
Farmers are locked in an arms race between ever-stronger weeds and ever-stronger weed killers.
The dicamba system, approved for use for the first time this spring, was supposed to break the cycle and guarantee weed control in soybeans and cotton. The herbicide — used in combination with a genetically modified dicamba-resistant soybean — promises better control of unwanted plants such as pigweed, which has become resistant to common weed killers.
The problem, farmers and weed scientists say, is that dicamba has drifted from the fields where it was sprayed, damaging millions of acres of unprotected soybeans and other crops in what some are calling a man-made disaster. Critics say that the herbicide was approved by federal officials without enough data, particularly on the critical question of whether it could drift off target.
Government officials and manufacturers Monsanto and BASF deny the charge, saying the system worked as Congress designed it.
Leaves and a stalk from a soybean plant showing signs of being affected by dicamba. Photo by: Andrea Morales/For The Washington Post
“This should be a wake-up call,” said David Mortensen, a weed scientist at Pennsylvania State University.
Herbicide-resistant weeds are thought to cost U.S. agriculture millions of dollars per year in lost crops.
After the Environmental Protection Agency approved the updated formulation of the herbicide for use this spring and summer, farmers across the country planted more than 20 million acres of dicamba-resistant soybeans, according to Monsanto.
But as dicamba use has increased, so too have reports that it “volatilizes,” or re-vaporizes and travels to other fields. That harms nearby trees, such as the dogwood outside Blytheville, as well as nonresistant soybeans, fruits and vegetables, and plants used as habitats by bees and other pollinators.
According to a 2004 assessment, dicamba is 75 to 400 times more dangerous to off-target plants than the common weed killer glyphosate, even at very low doses. It is particularly toxic to soybeans — the very crop it was designed to protect — that haven’t been modified for resistance.
Kevin Bradley, a University of Missouri researcher, estimates that more than 3.1 million acres of soybeans have been damaged by dicamba in at least 16 states, including major producers such as Iowa, Illinois and Minnesota. That figure is probably low, according to researchers, and it represents almost 4 percent of all U.S. soybean acres.
“It’s really hard to get a handle on how widespread the damage is,” said Bob Hartzler, a professor of agronomy at Iowa State University. “But I’ve come to the conclusion that [dicamba] is not manageable.”
The dicamba crisis comes on top of lower-than-forecast soybean prices and 14 straight quarters of declining farm income. The pressures on farmers are intense.
One Arkansas man is facing murder charges after he shot a farmer who had come to confront him about dicamba drift, according to law enforcement officials.
Thirty minutes down the road, Arkansas farmer Wally Smith is unsure how much more he can take.
Smith’s farm employs five people — including his son, Hughes, his nephew, Brian, and the farm manager, Mayes. None of the men are quite sure what else they’d do for work in this corner of Mississippi County.
Dicamba has hit the Blytheville — pronounced “Bly-vul” — region hard. For miles in any direction out of town, the soybeans that stretch from the road to the distant tree line are curled and stunted. A nearby organic farm suspended its summer sales after finding dicamba contamination in its produce.
Eddie Dunigan, Photo by: center
“This is a fact,” the elder Smith said. “If the yield goes down, we’ll be out of business.”
The new formulations of dicamba were approved on the promise that they were less risky and volatile than earlier versions.
Critics say that the approval process proceeded without adequate data and under enormous pressure from state agriculture departments, industry groups and farmers associations. Those groups said that farmers desperately needed the new herbicide to control glyphosate-resistant weeds, which can take over fields and deprive soybeans of sunlight and nutrients.
Such weeds have grown stronger and more numerous over the past 20 years — a result of herbicide overuse. By spraying so much glyphosate, farmers inadvertently caused weeds to evolve resistant traits more quickly.
But during a July 29 call with EPA officials, a dozen state weed scientists expressed unanimous concern that dicamba is more volatile than manufacturers have indicated, according to several scientists on the call. Field tests by researchers at the Universities of Missouri, Tennessee and Arkansas have since found that the new dicamba herbicides can volatilize and float to other fields as long as 72 hours after application.
Regulators did not have access to much of this data. Although Monsanto and BASF submitted hundreds of studies to the EPA, only a handful of reports considered volatility in a real-world field setting, as opposed to a greenhouse or a lab, according to regulatory filings. Under EPA rules, manufacturers are responsible for funding and conducting the safety tests the agency uses to evaluate products.
Pigweed, a highly competitive plant that grows in cotton and soybean fields and has developed resistance to some pesticides, grows tall over soybean fields weakened by nearby dicamba use. Photo by: Andrea Morales/For The Washington Post
Frustrated scientists say that allowed chemical companies to cherry-pick the data available to regulators.
“Monsanto in particular did very little volatility field work,” said Jason Norsworthy, an agronomy professor at the University of Arkansas who was denied access to test the volatility of Monsanto’s product.
The EPA and chemical manufacturers deny that there was anything amiss in the dicamba approval process.
“The applicant for registration is required to submit the required data to support registration,” the agency said in a statement. “Congress placed this obligation on the pesticide manufacturer rather than requiring others to develop and fund such data development.”
Manufacturers say that volatility is not to blame. In a statement, BASF spokeswoman Odessa Patricia Hines said the company brought its dicamba product to market “after years of research, farm trials and reviews by universities and regulatory authorities.”
Scott Partridge, Monsanto’s vice president of global strategy, thinks some farmers have illegally sprayed older, more volatile dicamba formulations or used the herbicide with the wrong equipment.
The company, which last year approved $1 billion investment in its dicamba production plant over the next three years, has deployed a fleet of agronomists and climate scientists to figure out what went wrong.
“We’re visiting every grower and every field,” Partridge said. “If there are improvements that can be made to this product, we’re going to do it.”
Regulators in the most-affected states are also taking action. In July, Arkansas banned spraying for the remainder of the season and raised the penalties on illegal applications.
Missouri and Tennessee have tightened their rules on dicamba use, while nearly a dozen states have complained to the EPA.
The agency signaled in early August that it might consider taking the new dicamba herbicides off the market, according to several scientists who spoke to regulators.
The agency would not comment directly on its plans. “EPA is very concerned about the recent reports of crop damage related to the use of dicamba in Arkansas and elsewhere,” an agency representative said.
Meanwhile, a class-action lawsuit alleges that dicamba manufacturers misrepresented the risk of their products. The Smiths are considering signing up. Monsanto says the suit is baseless.
There are also early indications that dicamba may not work for long. Researchers have shown that pigweed can develop dicamba resistance within as few as three years. Suspected instances of dicamba-resistant pigweed have been found in Tennessee and Arkansas.
A spokeswoman for Monsanto said the company was “not aware of any confirmed instances of pigweed resistance” to dicamba.
Soybean farmer Brad Rose's truck kicks up dust while heading down a road near his farm. Photo by: Andrea Morales/For The Washington Post
“We’re on a road to nowhere,” said Nathan Donley, a senior scientist at the Center for Biological Diversity. “The next story is resistance to a third chemical, and then a fourth chemical — you don’t have to be a rocket scientist to see where that will end.
“The real issue here is that people are using ever-more complicated combinations of poisons on crops, with ever-more complex consequences.”
In Blytheville, at least, one consequence is increasingly obvious: It’s a short, scraggly plant with cupped green leaves and a few empty pods hanging near its stem. At this time of year, this plant should have more pods and be eight inches taller, Mayes said.
“This is what we’re dealing with here,” he said, before shaking his head and turning back to his truck. “We go to work every day wondering if next year we’re still going to have a job.”