There was a story today in the New York Times (“Farmers Cope with Roundup-Resistant Weeds”) about glyphosate-resistant weeds, or as the headline states – Roundup-resistant weeds. (Glyphosate is the active ingredient in Roundup. Its success has made the two interchangeable similar to the case of facial tissue and the brand name Kleenex).
This is the second story in recent weeks about “superweeds,” as the mainstream media has sensationally dubbed the weed resistance issue.
Overall the NYT story talks about the positive contributions of biotechnology on weed control—increase in no-till, the switch from alternative herbicides to Roundup, reduced soil erosion, less herbicides/fertilizer runoff into waterways, and an easier management system for farmers – but also warns that farmers are having to resort to some of the old ways of killing weeds because of weed resistance.
These articles seem a bit late to the game since we’ve been dealing with glyphosate-resistant weeds for 10 years now. The first resistant weed –horseweed – was discovered in Delaware in 2000. But, I guess the mainstream media has decided weed resistance is now in vogue.
A few notes about resistance:
- After four decades of use, there are 18 weeds that have become resistant (10 in the U.S.) Glyphosate is the most widely used herbicide, and still controls more than 300 different types of weeds. Not a bad track record.
- Weed resistance is not unique to glyphosate and is a potential issue with any herbicide. Herbicide-resistant weeds have been around since the 1950s. For an exhaustive list of different herbicides and their resistant weeds, check out the International Survey of Herbicide-Resistant Weeds. The survey also includes dates when the resistance was identified as well as location by country and state/region.
- Overuse of a glyphosate is often stated as one of the key reasons behind resistance. In actuality, it’s over reliance, which is different. Over reliance on a single herbicide increases the selection pressure.* As does growing a single crop with no rotation (ex. corn over and over again on the same field).
- Underuse of the herbicide can also be a contributing factor. If farmers reduce application rates to save money, that also increases the selection pressure. It’s similar to what happens when your doctor tells you to take the prescribed antibiotics for 10 days, and you only do it for 5. You’re increasing the risk for your body to become resistant to the antibiotic.
- And finally, what the heck is a superweed? Seriously, this term gets thrown around a lot, primarily in non-agriculture venues. I imagine pigweed standing tall with a red cape, refusing to die. Glyphosate may no longer be able to kill these weeds, but that by itself doesn’t make them “superweeds.” There was a time when glyphosate wasn’t around, and guess what? These weeds existed.
We know resistant weeds are a concern for our customers. Over the past 10 years, we’ve worked with farmers, weed scientists and public institutions to monitor and research the issue and to provide recommendations on managing resistant weeds as well as prevention for further resistance. These best management practices have evolved over time as we have learned more.
Today, those practices include proper application rates, the use of other herbicides as necessary, rotation of crops and tillage. We work to broadly encourage those practices among farmers via communications on our product labels, in our technology use guides, print literature, and via professional websites to growers, retailers and farm consultants.
*What is selection pressure? Well, imagine that you have a whole population of pigweed in a field. Some of those pigweeds can naturally resist the effects of a particular herbicide. You spray the herbicide, and if you leave these weeds alive in the field, they can come back the next year and are harder to control.
For more information on weed resistance, check out these links:
WeedTool.com – (includes fairly comprehensive list of resources: university weed science departments, industry organization learning modules,
Weed Resistance and Benefits of Diversified Weed Management Programs (Monsanto)
For the Record – Science – Weed Resistance (Monsanto)
Weed Resistance Risk Assessment (Monsanto)