The following is a portion of an article published by Andrew Kniss on Control Freaks, Wyoming Weed Science in (almost) Real Time. CLICK HERE to read the original article
A couple weeks ago, Chipotle announced they were removing genetically engineered crops (called GMOs) from their menu. Kind of. As you might expect, the announcement was covered widely in the media. Interestingly, though, most of the coverage wasn’t very positive. There’s a fairly long list of responses to the Chipotle decision if you’d like to read more about it. A variety of issues are covered in those responses, but I wanted to take a deeper look into the impact this switch might have on pesticide use.
Superweeds
In his response to the Chipotle announcement, Dan Charles at NPR brought attention to one aspect that he called the “superweed” double standard:
As an example of the ways that GMOs can damage the environment, Chipotle points to the problems caused by herbicide-tolerant GMO crops and how they encourage farmers to use a single herbicide, usually glyphosate, or Roundup. This, in turn, has led to the emergence of herbicide-resistant weeds, which Chipotle calls “superweeds.”
Chipotle’s answer to this, per its new non-GMO policy, is to switch from soybean oil to sunflower oil.
The problem is, many sunflower varieties, while not genetically modified, also are herbicide-tolerant. They were bred to tolerate a class of herbicides called ALS inhibitors. And since farmers starting relying on those herbicides, many weeds have evolved resistance to them. In fact, many more weeds have become resistant to ALS inhibitors than to glyphosate.
Why should Chipotle bemoan the emergence of weeds that are resistant to glyphosate, yet not to other weedkillers?
This is a point I’ve made several times in the past. There are two types of herbicide-resistant sunflower grown in the US, ExpressSun (from DuPont) varieties which are resistant to sulfonylurea herbicides, and Clearfield (from BASF) varieties that are resistant to imidazolinone herbicides. [Side note: if you want to avoid chemicals that are difficult to pronounce, neither of these options seem like a trade up.] Both the sulfonylurea and imidazolinone herbicides are ALS inhibitors, or WSSA Group 2 herbicides. Glyphosate, the herbicide used in the GMO crops that Chipotle removed, is an EPSP synthase inhibitor herbicide (WSSA Group 9). The figure below from weedscience.org (annotations in the plot regarding Chipotle are mine) shows the number of herbicide resistant weed species to these (and other) herbicides. Herbicides used in the non-GMO alternatives chosen by Chipotle have indeed contributed to more herbicide resistant weeds than the herbicides used in GMO crops. It is pretty clear that if “superweeds” are really a problem Chipotle wants to solve, this is a pretty strange direction to take.
I’d have to agree with the recent editorial in the Washington Post:
A related concern, according to [Chipotle], is that herbicide-resistant GMOs encourage overuse of herbicides. Wouldn’t the right response to that esoteric concern be to avoid products grown with herbicides?
But Chipotle isn’t sourcing ingredients that are herbicide (or other pesticide) free. The non-GMO crop alternatives they are using have almost certainly been sprayed with pesticides. But which pesticides?
“Toxic pesticides”
I’ve seen several suggestions that switching from GMO to non-GMO crops would result in an increase in pesticide use, or require the use of more toxic pesticides. For example, Rebecca Rupp, at National Geographic recently wrote:
In fact, evidence shows that use of GMO crops has sharply reduced use of pesticides…
And an Op-Ed in the LA Times by Steven Sexton and David Zilberman suggest that non-GMO crops require use of more toxic pesticides:
Moreover, herbicide-tolerant GM seed varieties allow farmers to replace toxic pesticides with more benign ones, and to forgo tilling operations that worsen soil depletion and nutrient runoff. Other GM seed varieties produce a naturally occurring protein that kills common crop pests and is, nevertheless, harmless to humans. These crops eliminate the need for some pesticides altogether.
Although these claims are common, I haven’t been able to find an analysis that really provides details on what Chipotle’s switch to non-GMO crops really means with respect to pesticide use. So my evenings for the last couple weeks have been spent looking up information about pesticides used in corn, soybean, and sunflower (I even looked up some canola data, if anyone is interested). Although it is impossible to determine exactly which pesticides would be used in the non-GMO crop fields where Chipotle is sourcing their ingredients, I think the information here should give some us a pretty good idea.
CLICK HERE to read the full article.
Andrew Kniss is an Associate Professor of Weed Ecology & Management in the Department of Plant Sciences at the University of Wyoming. He has a PhD in Agronomy with a minor in Statistics. Andrew's research program focuses on developing weed management programs in agronomic crops, especially sugarbeet, winter wheat, corn, and dry edible beans
Source: Control Freaks, Wyoming Weed Science in (almost) Real Time
