Recent blog posts and articles claiming that "superweeds" are getting stronger because of herbicide resistance have raised concerns amongst our readers. To help dig into the subject, we’ve enlisted the help of Dr. David Shaw from Mississippi State University.
Dr. David Shaw: Vice President for Research and Economic Development, Mississippi State University
How do you define superweeds?
Dr. Shaw: “First, it's a bit of a misnomer to call them "superweeds". They are the same as the other weeds; the only difference is that they have developed resistance to a specific herbicide.”
Are herbicide-resistant weeds a new problem?
Dr. Shaw: “We have had herbicide-resistant weeds since the 1950s, so this is not at all a new phenomenon. What is new, is the development of weeds that are specifically resistant to glyphosate."
"Glyphosate is the active ingredient in the herbicide called Roundup. Roundup found its way into headlines as the company that created Roundup developed Roundup-Ready crops. These crops have been genetically modified so that they are resistant to that specific herbicide, allowing farmers to spray their fields with the herbicide and kill only the weeds.
“Development of herbicide resistance is caused by the over-reliance on one specific herbicide (or active ingredient in that herbicide) for an extended period of time. In this case, we had millions of acres of crops that were treated with glyphosate, often exclusively, year after year. This, ultimately, can lead to resistance.”
So, if glyphosate can cause resistance, why do farmers use it?
Dr. Shaw: “Roundup Ready crops have allowed farmers to become much more efficient by controlling many different types of weeds, requiring less equipment and labor, and dramatically reducing their time working the land, which can result in excessive soil erosion.”
What are farmers doing to help stop these herbicide-resistant weeds?
Dr. Shaw: “Farmers have always been innovators, and implement other management practices to reduce weeds in their fields. That includes using alternate herbicides, working the land and even weeding by hand in some cases. There is no standard best approach because every farm is different. Different soils, different weeds and crops, and different farming systems mean that a one-size-fits-all approach won't work.
“In any case, when it comes to pest control tools, diversity is the key. Weed scientists have long known that the best management practice was integrating a variety of chemical and non-chemical weed control practices to proactively prevent resistance development. That usually includes rotating or mixing herbicides with different active ingredients. But it also calls for crop rotations, cover crops, tillage, row spacing and planting density, planting date, and many other factors that result in breaking the pattern each year and preventing the potential for resistance to develop."
Do herbicide-resistant weeds have an effect on the environment?
Dr. Shaw: “From an environmental standpoint, the challenge they pose falls into two categories.
1. First, in severe cases, tillage (working of the ground) is one of the few remaining options. For some soils that are highly erodible, this is causing growers to have to revert to tillage that causes more soil erosion.
2. Second, these weeds cause much more intensive management including implementing weed control measures and physical labor.
Are herbicide-resistant weeds going to affect the price of food at the grocery store?
Dr. Shaw: “They certainly have that potential. If resistance occurs, it costs the farmer more to manage it, so we are working very hard to teach farmers how to prevent the evolution of resistance before it happens.”
Will these weeds or the products used to kill them affect the health of my children?
Dr. Shaw: “No, these weeds are no different than their non-resistant counterparts. In all cases, the herbicides used to control them have been through extensive testing with the Environmental Protection Agency (EPA) to ensure that there are no detrimental human or animal health effects, and no adverse environmental impacts.”