Its Common Name is Satan

On October 27, 2016, Mike Wallace, a cotton and soybean farmer from Arkansas, met with Allan Jones, also a farmer and Mike’s neighbor. They met along a quiet road between their two farms. Their discussion began civil, but it quickly escalated. Then, suddenly, Jones drew his gun and shot Wallace. The farmer died before paramedics could arrive.

What drove Jones to make such a shocking and terrible decision? A weed. No, not marijuana – this was not a drug deal gone wrong. An actual crop weed: Palmer amaranth, also commonly called pigweed. While this may sound petty to non-farmers, this plant is so destructive in a field of cotton or soybeans that farmers will take some pretty drastic measures to get it under control. Unfortunately, this can lead to escalated tensions between once-peaceful neighbors.

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Palmer amaranth (Amaranthus palmeri). Image Credit: Pompilid via Wikipedia.

Bedeviling Farmers

Palmer amaranth (Amaranthus palmeri) is an annual broadleaf plant, related to spinach and beet. Unlike its cultivated cousins, though, the weed is not something you want to find in your garden. It can grow 3 inches a day, reach a height of 10 feet, and its stem can become as thick as a baseball bat. This incredible growth rate and size allows it to outcompete many crops. Unchecked, Palmer amaranth will lead to almost complete crop failure in corn and soybean, and weed control measures have cost the cotton industry over $1 billion.

Things have not always been this way. In 1996, Roundup Ready crops were introduced and killing Palmer amaranth was easy. Farmers would plant their genetically modified crop, spray some Roundup or other glyphosate formulation (i.e. the herbicide found in Roundup), and everything would die except for the crop. However, in 2005, glyphosate-resistant Palmer amaranth was identified in Georgia. Soon after, because of the large amounts of herbicide that farmers were using, glyphosate resistance began to evolve in Palmer amaranth all over the U.S. Farmers lost one of the most economic and environmentally-safe tools in their weed-killing arsenal.

A Faustian Bargain

Palmer amaranth has evolved resistance to 6 types of herbicides, including Roundup. Dicamba is one of the few that remain effective. In 2016, Monsanto, the corporation that makes Roundup and Roundup Ready crops, unveiled their newest product: Roundup Ready 2 Xtend crops, which can withstand glyphosate and dicamba. While somewhat more toxic than glyphosate, dicamba and ‘dicamba-ready’ crops offer farmers another tool in their arsenal against Palmer amaranth.

While seemingly good news, there was a problem: the current formulation of dicamba could not legally be used in most instances because it drifts too easily from the spot of application; a new, less volatile formulation should be available sometime in 2017. However, that didn’t stop farmers, like Jones, from illegally using the current formula on the new plants – they would employ whatever was available to control Palmer amaranth, even if their neighbors weren’t using the ‘dicamba-ready’ crops. Because of their un-neighborly actions, it is estimated that 200,000 acres of soybeans were damaged by dicamba drift in Arkansas, Tennessee, and Missouri in 2016. 

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Soybean leaves exhibiting ‘cupping’, a symptom of dicamba damage. Image Credit: uacescomm via Flickr.

Farmers that were caught illegally using the current formulation of dicamba were fined $1000 – a slap on the wrist to those that grow thousands of acres and run multimillion dollar operations. This light penalty agitated those like Wallace who followed the law, and it eventually led to his fatal confrontation with Jones.

Unfortunately, this probably won’t be the last difficult episode with Palmer amaranth. Farmers crave the good old days of Roundup Ready crops, and the ease with which they could kill the weed. Some see ‘dicamba-ready’ crops as a solution, but it probably won’t last. A recent study found that plants sprayed with dicamba became resistant after only three generations. Since there hasn’t been a new herbicide class in about 30 years, a farmer’s ‘chemical toolbox’ to avoid the evolution of herbicide resistance is limited. Managing something as bedeviling as Palmer amaranth will take both long-term strategies – such as utilizing many classes of herbicides and preventing the movement of weed seeds between fields – and cooperation between farmers.

About the Author

A transplant from Virginia (Hoos!), Greg Evans is a graduate student in the Plant Biology department at the University of Georgia studying herbicide and herbivory defenses in morning glories. When he’s not tangled up in weeds, Greg enjoys Ultimate Frisbee, bowling, and board games. He can be reached at gevans@uga.edu. More from Greg Evans.