Study seeks to find out if GMOs actually use more or less pesticides

September 07, 2016

As opinions continue to swirl in the debate regarding the benefits of genetically modified crops (or GMOs) scientists at Iowa State made a fresh attempt to answer one seemingly simple question: Did the development of those crops lead to more use of pesticides, or less?

To find this answer, the scientists used data from a private company, which gathered information about the farm practices of 5,000 randomly selected farmers who grew corn and soybeans, the two most widely planted crops in the country. According to one article, that information allowed detailed comparisons of pesticide use (including both insecticides and herbicides) on fields planted with GMO corn and soybeans, compared to non-GMO fields.

The scientists involved were seeking this answer as backers of GMOs point to the example of crops containing new genes that fight off insect pests, so farmers don't have to spray insecticides. However, biotech critics point to the example of crops that have been altered to tolerate specific weedkillers, like glyphosate, thus encouraging farmers to rely more heavily on those herbicides.

While it may seem like this research could provide a simple answer, the article goes on to explain that unfortunately, this study probably won't settle the debate.

One of the study's conclusions is straightforward and difficult to dispute. Genetically modified, insect-protected corn has allowed farmers to reduce their use of insecticides to fight the corn rootworm and the European corn borer. There is, however, concern that this effect won't last. Corn rootworms have evolved resistance to one of the genes that has been deployed against them.

When it comes to weedkillers, though, the picture gets becomes a little less clear. For one thing, the effect of GMOs has been different in corn than in soybeans. Farmers who switched to glyphosate-tolerant corn also switched herbicides, and used less total herbicide than farmers did on conventional corn — for a while. In the years since 2007, however, glyphosate-tolerant corn got sprayed with more weedkillers, as measured in kilograms per acre, than corn without that GMO trait.

Farmers who are growing genetically modified, glyphosate-tolerant soybeans, meanwhile, have been using more weedkillers than their non-GMO neighbors. In fact, that gap has been widening in recent years.

Edward Perry, a co-author of the study, said in the article that farmers may be using more herbicides on glyphosate-tolerant crops in recent years because they have to fight off an increasing number of weeds that have evolved to become resistant to glyphosate.

Complicating the picture even more is the fact that the war on weeds involves many different herbicides, and they vary tremendously in their environmental effects. The new study tries to account for that by comparing the "environmental impact quotient," or EIQ, of the herbicides sprayed on each field, in addition to their weight.

But Andrew Kniss, a weed scientist at the University of Wyoming, says the EIQ falls short as a measure of real environmental impact. "Toxicity can vary by a factor of 10 or a hundred," he said in the article. “The EIQ doesn't come anywhere close to capturing those large differences among chemicals.”

Much better, he continued, is a "risk quotient" measure that's used by the Environmental Protection Agency. "It is, frankly, disappointing to see continued use of the EIQ in the peer-reviewed literature.”

Kniss says the EIQ is such a crude measure that this study can't convincingly show whether GMO crops have been helpful or harmful to the environment.

This means, for now, that debate continues.

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Category: Food Safety, Genomics