Weeds that are highly resistant to herbicides are frequently referred to as ‘superweeds.’ These are nuisance weeds that have developed immunity to glyphosate, the active ingredient in Roundup. That product produced by Monsanto (now owned by Bayer AG) is frequently paired with GMO herbicide-tolerant crops, such as soybeans, corn, cotton and alfalfa in the US. These genetically modified crops are known as herbicide tolerant or Ht.
Advantages of Herbicide-GMO Seeds
Herbicide-GMO seeds have many advantages for farmers. These include lower costs, higher yields, and a reduction in the use of chemicals. But a growing weed resistance is beginning to compromise these advantages. This worries farmers who are being forced to deal with an expensive, growing weed problem. Also, consumers are worried about the increasing of trace chemicals such as glyphosate in the food supply. This is also fueling criticism from environmental groups who blame industrial farming and GMO crops for the increase in tougher weeds. They say that possible solutions introduced by the agrichemical industry, such as stacking herbicide resistant traits, could make the problem worse.
Some scientists claim that the challenge of weeds that are tolerant to herbicides pre-dated the introduction of GMO varieties in 1996. They note that some of the most serious weed problems affect non-GMO crops, such as sunflower plants. These scientists say that weeds are inevitable in conventional farming unless farmers are actively rotating and mixing chemicals and include some defenses that are non-herbicide in nature.
The Science and Politics of Superweeds
Some scientists are skeptical of the term superweeds. They argue that the term suggests that a weed is super strong or even invulnerable. But the truth is that that particular weed has simply developed a strong resistance to a certain herbicide. Andrew Kniss, Associate Professor of Weed Biology and Ecology at the University of Wyoming, has the following to say:
“Superweeds we hear about in news articles are not really much different than the herbicide-resistant weeds we have fought for half a century. That does not mean these herbicide-resistant weeds are not a problem. But it is not because they are resistant that they are a problem; weeds are a problem because they are aggressive, grow tall, damage equipment and produce a lot of seeds. Weeds generally are pretty ‘super’ by themselves. They have these traits whether they are resistant to a herbicide or not.’
The first herbicide-resistant weed that developed in the US was a type of spreading dayflower that was discovered in Hawaii in 1057. It was resistant to the herbicide 2,4-D. But while resistant weeds were around before glyphosate was introduced in 1974, they have spread rapidly in the following decades. The herbicide glyphosate was paired with several GMO crops in 1996, but it is just one of the herbicides to which the plants developed resistance. In fact, hundreds of species of weeds have developed tolerance to several types of herbicides in the past 40 years.
Farmers Believed Roundup Could Not Be Resisted
An early problem related to Roundup and glyphosate was that Monsanto spread the belief that Roundup was difficult to develop resistance to. Some farmers used it too much and took less care in doing other pest management practices that could have delayed the increase in weeds resistant to glyphosate.
Today, the scientific consensus is that herbicide resistance to some level is inevitable when farmers are too reliant on a single chemical for weed management. According to a report by the US Department of Agriculture’s Economic Research Service, sole reliance on glyphosate by many farmers is thought to be the major factor in the evolution of weeds that are resistant to glyphosate. Suggestions have been made that farmers could reduce the problem of herbicide resistance by alternating herbicides and crops annually. But even this may be inadequate. Studies indicate that mixing herbicides is more effective than rotating them to stop resistance to herbicides.
To better fight glyphosate weed resistance, crop scientists are developing newer GMO seeds that stack two or three traits that are resistant to various herbicides. One of those is glyphosate. Others are 2,4-D, dicamba or glufosinate. Many scientists think stacking these new herbicides – marketed as Enlist Duo by Dow AgroSciences and Roundup Extend by Monsanto, could be a more effective option against weeds that are resistant to traditional herbicides.
While many people are averse to the idea of spraying chemicals on crops, herbicides often are the most effective and environmentally-friendly solution. They reduce the need to plow and burn fields. Plus, by greatly increasing yields, there is far less clear-cutting of forests to produce farmable land.
- What Are Superweeds? (n.d.). Retrieved from https://gmo.geneticliteracyproject.org/FAQ/what-are-superweeds/
- Farmers Fight Explosion of Superweeds. (2018). Retrieved from https://www.scientificamerican.com/article/farmers-fight-explosion-of-superweeds/
- Kniss, Andrew, Ph.D. Professor of Weed Science, University of Wyoming. Retrieved from http://www.uwyo.edu/plantsciences/department-directory/kniss.html