Dicamba herbicide spawning new concerns

Scientific breakthroughs in genetically modified seeds have given new legs to a pesticide that previously had a limited role in the production of soybeans and cotton. But an explosive use in the herbicide dicamba across the agricultural landscape has brought with it thousands of complaints about damaged crops and a litany of possible health and environmental concerns.

Developed a half-century ago and sold under names like Banvel, Clarity, Diabo, Oracle, Vanquish and others, dicamba is a popular weedkiller used on agricultural fields, lawns, golf courses and other areas where broadleaf weeds are a problem. In farming, more than five million pounds of dicamba have been applied annually since at least 1994, primarily to corn crops. That's about 15 million acres of corn, 1.5 million acres of wheat and some three million lawns.

While dicamba is one of the most used herbicides, it pales in comparison to glyphosate, the top selling herbicide in the world, with some 180 million pounds applied in the United States each year. Best known under the brand name Roundup, the herbicide generates some $4 billion annually for pesticide manufacturer Monsanto. Key to the herbicide's success has been the development of genetically-modified soybean, corn, cotton and other "Roundup Ready" seeds that are tolerant of glyphosate. Used together, glyphosate can be applied directly on and around the genetically modified plants to kill weeds without damaging the crops.

But glyphosate's time at the top could be limited, as new batches of superweeds become resistant to the herbicide, and the pesticide's top producer, Monsanto, comes under fire in federal court and the European Union over claims that it causes cancer. That's where dicamba comes in, with Monsanto bringing the first dicamba-tolerant soybean and cotton seeds to the market in 2016. Monsanto now believes dicamba's use will increase from about 233,000 pounds per year in soybean production to 20.5 million pounds, while its use in cotton production is expected to go from 364,000 pounds to as much as 5.2 million.

Still, significant problems could prevent dicamba from being the savior to the company and farmers looking for an added agent or alternative to glyphosate. For one, health and environment groups claim dicamba carries with it some of the same issues as glyphosate, linking it to non-Hodgkins lymphoma, a type of blood cancer; genetic blood damage in humans; and fetal development issues, birth defects, decreases in body weight, liver damage, eye damage and several types of cancers in laboratory animal tests.

Dicamba also volatilizes, or evaporates, when applied in temperatures above 85 degrees, meaning it has a tendency to create vapor clouds during hot summer months that are capable of drifting up to 10 miles. Such drifts have resulted in more than 2,000 complaints of crop damage from off-site farmers and allegedly has damaged over 3.1 million acres of land, causing at least two states to temporarily halt the use of the herbicide.

In Michigan, dicamba has already been used on corn crops for decades. With no significant cotton crop in the state, new uses of the herbicide would fall on soybeans, raising concern among farmers raising speciality food crops. Fruits and vegetables in the state are often grown in patches surrounded by soybean fields. Items like tomatoes, which are a broadleaf crop that is particularly susceptible to dicamba, could sustain major injury from vapor drift.

Another major concern for Michigan is the contamination of the state's surface waters, such as lakes, rivers, streams and ponds, one of the state's most widespread and valuable resources.

Dicamba is relatively water soluble and has the ability to easily contaminate ground and surface water. While officials at the Michigan Department of Environmental Quality (DEQ) haven't had any recorded instances of dicamba contaminating ground or surface water, a 1992 study found groundwater contamination from the herbicide in 17 states in the Pacific Northwest from 1971 to 1992. It has also been found in the drinking water in Cincinnati, New Orleans, Philadelphia and Seattle. Periodic tests of unregulated drinking water contaminants conducted by the Detroit Water and Sewerage Department looked for and didn't find any traces of dicamba.

Still, consider that dicamba's use is expected to increase by several million pounds in the near future, and it's not surprising that concern from the agriculture industry and the health and environment community are at an all time high over the herbicide.

"It is widely researched, but apparently not widely known that increasing an area treated and amount applied of herbicide increases the likelihood that herbicides will appear in surface and groundwater," Pennsylvania State University professor David Mortensen, a specialist in weed and plant ecology, said in a statement to the Environmental Protection Agency (EPA) opposing registering new uses of the dicamba.

Not only did he say expanded use exacerbates weed resistance and cause problems related to vapor drift, he said the expansion would increase water contamination and human exposure.

"The fact that we would increase dicamba use by three to seven fold at a time when we are working hard to reduce human and natural systems exposure to such compounds goes against national policy, concerns about human health and the integrity of the

agro-ecological matrix," he said.

Despite these concerns and others expressed in some of the some 16,000 comments the EPA received, the agency in December of 2016 approved expanding dicamba's use from grasses, corn and some other limited uses to genetically-modified cotton and soybeans that had already been released in the market. The approval was initially viewed as a victory for row crops which could be able to use the herbicide in conjunction with the new seeds as a new tool to fight weeds.

"Low-volatility dicamba formulations with VaporGrip Technology are designed to give soybean farmers additional tools to control glyphosate-resistant and tough-to-control broadleaf weeds," Mike Frank, vice president and CCO of Monsanto said months prior to the EPA's approval.

In July of 2016, months prior to the EPA's approval of dicamba's expanded use, Monsanto and DuPont entered a supply agreement in which Monsanto would supply its dicamba-tolerant Roundup Ready2 Xtend soybeans, a modified version of its glyphosate-resistant seeds, and DuPont would sell the matching herbicide as FeXapan Herbicide Plus VaporGrip Technology.

The agreement and subsequent registration for the new dicamba formulations came after the dicamba-resistant seeds hit the market and were purchased by farmers. The delay meant farmers who purchased the seeds didn't yet have an approved dicamba herbicide to use in conjunction with growing.

As a result, it’s believed crops around the country, particularly in the southern United States, were damaged by farmers who used older formulations of dicamba that doesn't have added properties to reduce vapor drift. How much of the estimated three million acres of damage came from misuse of herbicide product isn't yet known.

As of September 15, 2017, a total of 2,610 official complaints and subsequent investigations of dicamba crop injury were filed with departments of agriculture in 28 states, including 967 in Arkansas and 310 in Missouri, according to weed experts monitoring the issue and compiled in a report by the the Association of American Pesticide Control.

At least a half-dozen lawsuits have been filed against the herbicide manufacturers or the EPA. Additionally, some states where crop damage has been particularly bad have passed additional restrictions and/or bans of dicamba use. The EPA also has announced it is investigating whether additional restrictions will be needed in the face of millions of acres of crop injuries.

"We are reviewing the current use restrictions on the labels for these dicamba formulations in light of the incidents that have been reported this year," an EPA spokesman said. "The underlying causes of the various damage incidents are not yet clear. But the EPA is reviewing all available information carefully. We will rely on the best information available to inform of any regulatory change."

In January of 2017, the Center for Food Safety, along with the National Family Farm Coalition, the Pesticide Action Network of North America and the Center for Biological Diversity filed suit in the U.S. 9th District Court of Appeals in response to the EPA's approval of Monsanto's registration of dicamba for use on genetically engineered crops.

"The catastrophe of drift damage that has happened this year across millions of acres of farmland was foreseen by those of us that warned the EPA not to rubber stamp Monsanto's pesticide," said George Kimball, legal director for the Center for Food Safety. "Our litigation seeks to have that EPA approval overturned as unlawful, and thus protect farmers and the environment."

Specifically, the petition of review filed requests of the court review the EPA's final order, and found the agency violated its duties under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) by issuing the order; violated the agency's duties under the Endangered Species Act by failing to consult with the US Fish and Wildlife Service or the National Marine Fisheries Service to ensure that registering dicamba for use wouldn't jeopardize any listed species or destroy any of their critical habitats; and to grant relief as may be appropriate.

Science policy analyst Bill Freese, with the Washington D.C.-based Center for Food Safety, a non-profit environmental organization focusing on food production technologies, said the center has broad concerns about the increased use of dicamba, including how it impacts the whole food chain, the agricultural industry and sustainability, as well as what is in the food we eat and whether it is dangerous.

"It started with Roundup Ready crops, which basically took over soybean, cotton, corn, sugarbeats, alfalfa and canola. The massive planting of these genetically-modified crops has facilitated the glyphosate use and glyphosate-resistant weeds. Now, they are already seeing the beginnings of dicamba-resistance in pigweed in Arkansas and Tennessee," he said. "It's an unsustainable system. I don't think it really is helping farmers. At best, it's like short-term relief, then when additional weed resistance arrives, it's like a pesticide treadmill. They will spray even more. It's certainly not in the farmer's long term interest."

Increased use of herbicides also isn't necessarily in the best interest of people exposed to it, either directly or in the food chain. While the new dicamba-resistant crops are designed to metabolize the herbicide, the safe levels of herbicide use is also a subject of debate.

"When you spray herbicides, you are going to get a certain level that is absorbed by the plant, and that will result in an edible portion of crop. For every pesticide approved, they set a tolerance level, and they aren't supposed to exceed that," Freese said. "The tolerance levels are set based on animal experiments, in which the EPA figures out what exposure they think is safe for human beings. Unfortunately, almost all of the tests are conducted by pesticide companies themselves, or they hire a firm to conduct the animal experiments. Based on that, they determine how much (people) can be exposed to on a daily basis without suffering any adverse effects. The EPA has raised the safe level of exposure to dicamba by about 300-fold since the 1980s. That's a pretty huge increase in what is considered safe. Based on the data, I don't see good scientific reasons for raising the levels.

“What's interesting is that the safe level tends to go up with the use of an herbicide. As it's used more, you see more in food and greater exposure. I think we can see a number of cases where the EPA is playing with the science to say that it's not as hazardous as we thought. But the real reason is that the companies want to use more herbicide on more crops, and the EPA justifies that at the maximum exposure levels."

Freese said the EPA has also been loosening its standards on whether other herbicides cause cancer, noting the EPA's findings regarding glyphosate and the agency's determination that it doesn't likely cause cancer that has mixed review by the Federal Insecticide, Fungicide and Rodeticide Act's (FIFRA) scientific advisory panel.

FIFRA prescribes the guidelines the EPA uses for regulating the sale and distribution of pesticides in the country. It also sets rules for the EPA when considering whether to register a pesticide for use in the country. While dicamba has been registered for use in the United States for decades, those uses had been limited to corn and some other uses.

During 2015 and 2016, the EPA received thousands of comments regarding authorizing the expanded use of dicamba. The companies requesting the registration of their products – Monsanto, DuPont and BASF – made their request based on claims that their new formulas has special properties that reduce the herbicide's tendency to drift.

The Center for Food Safety was one of the organizations that opposed the new registration, based on several concerns, including human health. Many others also expressed concerns that dicamba is an older chemical with concerns about being a possible carcinogenic.

A 1992 epidemiology study by the National Cancer Institute found exposure to dicamba doubled farmers' risk of contracting non-Hodgkins lymphoma two decades after exposure. Another study funded by the EPA found that 1.4 percent of a sample population had dicamba residues in their urine, suggesting about 2.3 million Americans are contaminated with dicamba.

In its response to public comments, the EPA dismissed concerns about cancer, saying dicamba "is not likely to be a carcinogenic to humans." That decision, the EPA said in its response, was based on a lack of findings in the cancer studies of rats and mice, "which were tested at adequate dose levels to assess the carcinogenicity of dicamba."

Further, while the EPA stated dicamba "induced chromosomal aberrations in human lymphocytes in vitro," the genotoxicity was negative in vitro in mice studies. It further stated a study linking cancer to pesticide applicators "didn't indicate any 'strong associations' between dicamba exposure and overall or site specific cancer risk."

"They are basically trying to claim that they don't need to incorporate higher doses," Freese said about the EPA's response. "It's a way to compare results of high-dose groups with a control group, and you're looking at incidence rates."

For instance, Freese said, a carcinogenic rate of four out of every 60 test subjects that received high doses of dicamba showed problems, while none of the animals in the control group, or those not receiving dicamba, didn't. From a statistical standpoint, he said the four that showed problems isn't a high enough number for a strong or significant association.

"In this case, it's just barely not significant, but there is a significant trend, which is a second way of looking at this," he said. "You look at statistics to see if there is a trend, and not just looking at the high-dose group and the control group – you look at all of them. You had four in the high-dose group, and four in the mid-dose group. If you look at those together, there is a significant trend. But the EPA has guidelines, so they don't both have to show significance. They shouldn't have taken that as evidence."

For humans, the main route of exposure to dicamba is either through direct contact in its use or from eating foods treated with dicamba prior to the plant's ability to metabolize it. While the vast majority of corn and soybeans treated with dicamba are ultimately used for livestock feed, there is little known about the effects of dicamba-treated feed on the food chain. Further, what research has been done is typically conducted by the herbicide manufacturers themselves. Still, the United States Department of Agriculture sets "grazing restrictions" on pastures and crops treated with dicamba that are used for feed.

"The effect of a chemical or its breakdown products on livestock or retention in the animal's body may not be known," the USDA states in its restrictions. "The concern is that herbicdes could be passed in the milk of lactating animals or cause abortion in pregnant animals. The chemical may also have the potential to be retained by the animals and be present in the slaughtered carcass."

The Pesticide Action Network of North America also opposed the EPA's new registration of dicamba herbicides, citing harm to farmers, the environment human health and socio-cultural harm to rural communities arising from increased conflict between neighboring farmers around issues of drift, crop damage and liability.

Early reports of damage to soybean crops emerged in July of 2016, when an extension weed specialist at the University of Arkansas noted issues in fields in that state, citing a 10-percent yield loss from low-level use of dicamba by farmers.

Conflict among farmers using dicamba herbicides at neighboring farms quickly escalated. Dicamba drift, particularly drift produced from older formulations that hadn't been approved for use on genetically-modified (GM) cotton and soybean, can seriously damage non-GM soybean, as well as other sensitive speciality crops, such as tomatoes, potatoes, ornamental trees and other crops.

In October 2016, an Arkansas farmer was shot and killed following a dispute with a neighbor over dicamba drift.

While tensions haven't reached fatal levels in Michigan, there remains a rift between some farmers over whether the product should be used in the state. Even within the Michigan Farm Bureau, specialty farm experts say they don't like dicamba products used around their crops because of the potential for drift and damage.

"In terms of specialty crops, our growers aren't fans of it," said Kevin Robson, horticulture and industry relations specialist for Michigan Farm Bureau. "We have a lot of growers of specialty crops, like Red Gold Tomatoes, and they are nervous. They don't want a grower to put an application on this and have it off-target their tomatoes. It's possible there's been drift out there in Michigan – we can't say it hasn't happened – but as far as we know, there haven't been problems in Michigan."

The concern differs from the view of Kate Thiel, a field crop specialist with Michigan Farm Bureau, who said growers want access to new applications.

"At the end of the day, we are coming up against resistance issues, and these are important tools in our tool box," she said. "We want to couple that with good standards and best practices, and our members are focused on that, as well."

Although Robson said he and Thiel are on different sides of the issue, Farm Bureau is supportive of new herbicide tools and proper use of those, especially since it has already been approved and available for use.

"It's a new formulation, and not like the others that you're having horror stories with in other states, so it doesn't have the volatility and tendency to drift. I'm trying to convince any growers that I work with that that's the case, but it's a moot conversation," Robson said. "These are new technologies, and Farm Bureau isn't going deny access to one grower to benefit another. We find we have members on both sides of the fence."

Row crop farmers relying on the commodities are likely to turn to dicamba in the future as a standard control for weeds.

"As some of these situations are figured out, I do think it will continue to grow in popularity," Thiel said. "Farmers will procede with caution, but I think you will see an increase in utilization moving forward as it becomes a viabile option to folks."

Still, commodities farmers facing tight profit margins are likely to embrace any new technology that will help a high yield of their crop.

"Farming is a very break-even kind of business, at best, and if you're highly leveraged, these are going to be really difficult times," said Mike Staton, a soybean specialist with MSU Extension. "Margins are incredibly tight. Soybeans are looking better than corn in the past couple of years, and that's a change."

To reduce costs, farmers look to finding seeds that will provide the best crop yield. For the past three years, planting research has allowed farmers to plant less seed without giving up yield. The new dicamba-resistant seeds offer a potential way to boost that yield.

In Michigan, an increased use of dicamba has primarily caught the attention of farmers. And, while the herbicide hasn't been known to have a presence in any surface waters, according to the Michigan DEQ's Surface Water Program officials, it's also one that hasn't previously been on the radar.

Because dicamba isn't a "restricted use" herbicide, the state's department of agriculture doesn't track the amount of the chemical sold each year, as it does with some other pesticides. However, dicamba's use will undoubtedly increase in Michigan as soybeans continue to be a top agricultural commodity in the state.

"Nationally, we have a very large crop that's expected," said Mark Seamon, research coordinator with the Michigan Soybean Promotion Committee. "It seems clear we won't have a record this year in terms of yield-per-acre, but this year is good, but short of great. The biggest challenge is weather in the late season and lack of rainfall."

About 97-percent of Michigan's soybean crop is used for livestock feed, oil and other industrial uses. A small percent is used for human food consumption, which is typically sold in the export market. Seamon said soybeans used for food products don't typically contain genetically modified seeds, as they are a premium market product.

Pesticide manufacturer BASF gained registration approval from the EPA in December of 2016 for Engenia herbicide, to be used in dicamba-resistant soybeans and cotton. The company claims the new formula reduces drift by 70 percent when compared to previous formulations. Other products approved by the EPA include DuPont FeXapan Herbicide Plus VaporGrip Technology; Engenia Herbicide; and Xtendimax with VaportGrip Technology.

While the newer formulations of dicamba herbicides are marketed to have reduced drift properties, a lawsuit filed against the manufacturers claims dicamba-resistant seeds were sold and marketed by representatives who instructed farmers to use older formulations because they expected approval by the EPA to make the issue a moot point. The site also claims the products were rushed, and new formulas still don't have proper volatilization reduction, as shown by tests conducted after the products reached the market.

A class action lawsuit filed in a federal court in Missouri in July 2017, against Monsanto, BASF and DuPont by a group of farmers claiming Monsanto released dicamba-resistant cotton and soybean seeds prior to approval of an appropriate formulation despite warnings that it would pose a risk to crops. The site also claims Monsanto instructed farmers to use older formulations of dicamba herbicide despite the fact that doing so would be illegal.

"This was Monsanto's real plan: publicly appear as if it were complying, while allowing its seed representatives to tell farmers the opposite in person," the site states. "Their sales pitch assures purchasers that off-label and illegal uses of dicamba would be 'just fine.'"

The suit also claims the defendants relied on misleading volatility testing and withheld crucial information from the EPA. For example, the plaintiffs say Monsanto only tested volatility of the new formulations relative to other dicamba formulations and not determining a safe level of volatility; and, that university scientists asked to test the herbicide weren't allowed to test its volatilization, despite receiving multiple requests.

"When specifically asked about this on or about August 8, 2016, a Monsanto representative (Boyd Carey) stated to the Arkansas Plant Board such tests would not be allowed because the results might jeopardize Monsanto's registrations," court documents state. "The result: the approved over-the-top dicamba formulations, even if properly applied, were not non-drifting or non-volatilizing."

Many farmers who supported the new dicamba formulations did so on the premise that proper education, training and following best management practices prescribed on the pesticide's label would ensure safety and improve weed control.

The state of Michigan is among the top 12 producers of soybeans in the country, just behind Arkansas, which is 11th in ranking. As a commodity, the crop was valued at some $850 million in 2015, the second most important in the state to corn. Among the top challenges to that production is weed management, according to the Michigan Agribusiness Association.

"Our crop advisors, custom applicators and producers in Michigan are well-equipped to properly manage pesticide products in accordance with label specifications, and are committed to responsible stewardship of pest control products," Tim Boring, vice president of the association said in a statement to the EPA. "Training and educational programs regarding best management practices for dicamba use are slated to continue in the state as the approval progresses. Our association urges the EPA to approve the registration of dicamba use on dicamba-tolerant cotton and soybeans."

As of October 1, two official complaints have been filed with the Michigan Department of Agriculture and Rural Development (MDARD) regarding alleged crop injury from dicamba drift, said Brian Verhougstraete, with MDARD's Pesticide Registration and Certification Division.

"Dicamba does have a tendency to drift and volatize – that's what's happening down south. The jury is still out, but there's been a lot of misuse. The new product wasn't available to be sprayed, so they were using what was registered for corn and using it on soybean. There's probably still some of that going on in the south," he said. "In Michigan, we didn't have any cases we are aware of where people (had crop injury) using new products. We are hearing damage is out there, but we haven't received official complaints on those."

One official complaint, which remains open as of publication of this article, suggests tomatoes were damaged by off-target movement of dicamba. The issue occurred in Eaton County.

The second Michigan case occurred in Genesee County and involved damage to soybeans. The case has since been closed, but Verhougstraete said the damage was apparently caused by dicamba. While he said the test results of the damaged crops came back negative for dicamba, those findings aren't uncommon as dicamba and its metabolite breakdown very quickly in the environment, "usually before crop damage is observed."

"As a result, it's very hard to verify suspected dicamba damage through laboratory analysis," he said.

Despite assurances that new dicamba formulations won't damage crops through vapor drift, some experts have criticized the labels and instructions, and questioned whether the technology itself is safe enough to be used under any conditions. For instance, weed expert Larry Steckel of the University of Tennessee said the label associated with the approved low-volatility dicamba formulations called XtendiMax, FeXpan and Engenia are already complicated without further restrictions.

"Following them as they are now is a Herculean task," he is quoted stating in the lawsuit. "Talk about threading the needle – you can't spray when it's too windy. You can't spray under 3 miles per hour. You got to keep the boom down – there are so many things.

"It looks good on paper, but when a farmer or applicator is trying to actually execute that over thousands of acres covering several counties, it's almost impossible."

As the likeliness of crop damage increases with the increased use of dicamba and vapor drift, more and more farmers are expected to use Xtend soybean, cotton and other dicamba-resistant products, the site contends. With a price of $5 to $10 per acre premium for its dicamba-resistant soybeans, Monsanto estimated earnings of $15 million to $30 million with the initial launch of the seeds, targeting about 3 million acres. But increased demand could raise that figure to some 250 million acres of soybeans, which would increase revenue to $1.25 to $2.5 billion a year, according to the lawsuit.

"This is not an anti-GMO lawsuit; it's a lawsuit about corporate greed, a rush to market, and the resulting fallout," the plaintiffs state. "With a global population expected to exceed nine billion by 2050, food production must grow 70 percent to feed the world. While there are some that believe organic or non-GMO crops are a better choice, the math is clear – without GMO crops, there will not be enough food to feed the world.

"Despite this reality, the biotech industry has repeatedly proven there are risks of harm if GMO crops are not handled responsibly... although the defendants here pledged to act responsibly, defendants acted selfishly, focused on profits and ignored their responsibilities to the market."

Additional lawsuits have been filed against Monsanto, DuPont and BASF in response to crop injury from alleged dicamba drift. An Illinois farmer filed a federal suit claiming damage to his soybean and pumpkin crops. A Missouri orchard filed suit in November 2016, after 7,000 peach trees in 2016 and 30,000 in 2007 were damaged. A suit spearheaded by a Missouri farmer in January 2017 against Monsanto now includes farmers from Alabama, Arkansas, Illinois, Kentucky, Minnesota, Mississipi, North Carolina, Tennessee and Texas. Six Arkansas farms filed suit in July 2017 under the name Bruce Farms Partnership. Fourteen Arkansas producers filed sit against Monsanto and BASF in July under the name B&L Farms.

Under FIFRA, the EPA regulates the sale, distribution and use of pesticides in the United States. When certain federal criteria are met, states also have regulatory authority. Under the federal law, the label on a pesticide package or container and the accompanying instructions are part of pesticide regulation. The label provides key information about how to safely handle and use the pesticide product to avoid harm human health and the environment. Misuse of the pesticide outside of label instructions is a violation of federal law.

In January of 2017, Arkansas Governor Asa Hutchinson approved that state's plant board's recommendation to temporarily ban some uses of dicamba. Six months later, the state placed a 120-day ban on spraying of dicamba on crops other than pasture land, with the governor saying "the volume of complaints do justify emergency action."

In July, Missouri also halted the sale and use, or removal order, of the new dicamba formulations in that state, where more than 200,000 acres of soybeans, and more than 6,500 acres of other crops, including certified organic vegetable farms, were effected.

The Tennessee Department of Agriculture in July also enacted new rules on dicamba sales in that state, including the requirement of a special license for new formulations, banning use of older formulations for the season and new record keeping requirements.

Verhougstraete, with the Michigan Department of Agriculture, said that from an agricultural standpoint, dicamba herbicides are less of a concern in Michigan.

"It's a big issue, but not a big issue in Michigan," he said. "There are several factors in that. What is driving use is weeds that are resistant to other chemistry, particularly Roundup. That product was really overused, and weeds developed resistance. All the weeds in the south are so resistant, they had to use something else. Up here, we don't have nearly as big as an issue."

While dicamba has been used on corn and lawns for generations, Verhougstraete said temperatures are much lower when applied to corn, so the possibility of drift is far lower. And, while the department receives complaints about dicamba in relation to lawns, he said those complaints typically involve misapplication rather than an issue with the specific properties of dicamba.

Christy Sprague, a weed specialist and professor with Michigan State University Extension, confirmed that while there are some glyphosate-resistant weeds in Michigan, there are far fewer in species and number than in some other states where drift problems are occurring.

"We do have some weed management challenges in Michigan with some herbicide-resistant weeds. It's not as much a serious problem as it is in some of the states to the south of us, but we are seeing them spread and the number of types (herbicide-resistant) weeds increase," she said. "Managing them has gotten a little tougher, not only because of glyphosate resistance, but other herbicides. There are limited options for managing those weeds."

Glyphosate-resistant weeds in Michigan that are problematic include horseweed, or mare's tail; Palmer Amaranth, a type of pigweed; and waterhemp.

Sprague said the overuse of herbicides does contribute to stronger, resistant weeds. That is part of the reason MSU Extension promotes a multi-faceted weed management approach, rather than relying on a particular herbicide.

"It goes back to the selection process. If you're relying on that technology to manage a problem, eventually over time these species could become resistant to that, also," she said. "We are looking at these new approaches as tools, not the only tool to manage these species." ­