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A chemical meant to save plants is actually killing them—and it’s spreading

An American farm is as much of a marvel of modern chemistry as it is of Mother Nature. This time of year, the landscapes across states like Nebraska, Missouri, and Arkansas are commanded by verdant fields of billowing corn and low-slung bushes growing soy. The crops’ successes can be attributed to the soils and the rains, of course. But for better or worse, we’ve also got synthetic fertilizers made from natural gas, insecticides designed to stop voracious critters, and weed killers like 3,6-dichloro-2-methoxybenzoic acid (better known as dicamba) to thank for the bounty.

But the relationship between plant and chemical has grown volatile.

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Featured

 Conversations about the Future of Dicamba: The Science Behind Off-Target Movement

Dicamba is an important herbicide for controlling post-emergent resistant weeds in soybean farming. Recently, the scientific community and general public have further examined off-target transport mechanisms (e.g., spray drift, volatilization, and tank contamination) and the visual responses of soybeans to ultralow dicamba concentrations. This paper synthesizes key chemical concepts and environmental processes associated with dicamba formulations, transport mechanisms, drift measurements, and plant responses.

 The Dicamba Papers: Key documents and analysis

Dicamba has been used by farmers since the 1960s but with limits that took into account the chemical’s propensity to drift and volatilize- moving far from where it was sprayed. When Monsanto’s popular glyphosate weed killing products, such as Roundup, started losing effectiveness due to widespread weed resistance, Monsanto decided to launch a dicamba cropping system similar to its popular Roundup Ready system, which paired glyphosate-tolerant seeds with glyphosate herbicides.

 The toxic pesticide dicamba is a threat to crops and human health. It’s time to ban it.

Dicamba is a weed killer that can drift for miles — staying in the air for up to 72 hours. When it drifts, it gets into the air we breathe and damages or destroys everything in its path — from home vegetable gardens to pollinator habitat. The only plants that can resist its effects are the genetically modified soybean and cotton plants that dicamba’s makers sell. Clearly, this weed killer cannot be used safely.

Articles of Interest

A Drift-Prone Weedkiller Still Damages Crops And Trees, Despite Attempts To Stop It

A controversial weedkiller called dicamba has divided rural communities and led to lawsuits over damage to orchards and vegetable crops. The chemical's main sponsor, the company Bayer, has promised to fix the problem. Now the billionaire founder of a top seed company is accusing Bayer of misleading people about the damage.

Controversial dicamba herbicides reapproved by the EPA

Given EPA-approved versions of dicamba have already damaged millions of US acres of crops and natural areas, there’s no reason to trust that the agency got it right this time.

Court overturns EPA approval of popular herbicide made by Monsanto

Ruling says EPA ignored clear evidence that the new herbicide would cause widespread damage to crops.

Dicamba: Concerns about health risks and crop damage

The EPA states that dicamba is not likely to be carcinogenic, but some studies have found an increased risk of cancer for users of dicamba. Studies have also linked dicamba exposure to increased odds of hypothyroidism.

Dicamba: Past, Present, and Future

The discovery of 2,4-D and other phenoxy herbicides in the 1940’s started the era of chemical weed management. Dicamba was first described in 1958, and registered for use in 1962. These herbicides mimic the action of auxin (indoleacetic acid), and are frequently referred to as growth regulator herbicides, synthetic auxins, or Group 4 herbicides.

Farmers’ Illegal Use of Herbicide Takes Toll on Neighboring Crops

Farmers in southern U.S. states have long battled weeds and destructive bugs, but this year they face a new threat: their neighbors. They say some growers are illegally spraying a powerful herbicide that is damaging hundreds of thousands of crop acres in Arkansas, Missouri and Tennessee, a trend that regulators, farmers and academics link to Monsanto Co.’s introduction this year of a new variety of genetically modified soybean.

How Dicamba Herbicides Are Harming Cultivated And Wild Landscapes

The level of injury to sensitive plants has been unprecedented since the adoption of new herbicide-resistant technologies that allow for the use of these volatile herbicides to continue later into the growing season, when temperatures are higher and dicamba is more likely to volatilize and move off-site.

Monsanto’s Weed Killer, Dicamba, Divides Farmers

But the seeds and the weed killer have turned some farmers — often customers of Monsanto, which sells both — against the company and alarmed regulators. Farmers who have not bought the expensive new seeds, which started to appear last year, are joining lawsuits, claiming that their crops have been damaged by dicamba that drifted onto their farms.

Study Finds an Association between Dicamba Use and Increased Risk of Developing Various Cancers

Dicamba—a benzoic acid chemical that controls broadleaf weeds—is one of the most widely applied herbicides in corn production. As a result of weed resistant to weed killers, farmers rely on increased, more frequent applications of dicamba as a control measure. However, with this increase in the chemical’s use, there is growing concern surrounding the dicamba’s potential human health effects.

The herbicide dicamba was supposed to solve farmers’ weed problems – instead, it’s making farming harder for many of them

I see dicamba drift as a symptom of a larger petrochemical dependency that threatens the viability of the U.S. food system. My research in this area makes clear that if federal agencies really want to help farmers solve weed problems, they would do well to look to agricultural innovators who are demonstrating that crops can be grown productively and profitably without relying so heavily on synthetic pesticides.

Uncovering dicamba’s wayward ways

Historically, dicamba has been a challenging herbicide to keep in place. Its high vapor pressure makes it one of the most volatile herbicides.

Resources

EPA

Dicamba is a selective systemic herbicide used to control annual, biennial and perennial broadleaf weeds in a variety of food and feed crops and in non-agricultural settings.

National Pesticide Information Center

Dicamba is similar to the herbicide 2,4-D. Both act like natural plant hormones known as auxins. These hormones help to control plant growth. When plants are treated with dicamba, they grow in abnormal and uncontrollable ways, and often, the plants die. Dicamba is used on many broadleaf weeds and woody plants.