The safety of GMO crops to humans, animals and the environment has been well established. The scientific consensus clearly states that consuming bioengineered foods has no effect on your health. Clearly, you can grab an ear of GMO corn, put some butter and a sprinkle of salt on it, and you will eat it with no negative health effects. And you’ll have a giant smile across your face.
But the anti-GMO forces have attempted to move the target. They have tried to claim that GMO crops are less productive and cost more to produce. That’s beyond the scope of this article, though there is some pretty good evidence that there is higher yield for bioengineered crops.
One of the more annoying aspects of the anti-GMO complains is conflating the genetically modified crop with the GMO crop pesticide. Invariably, some someone will post a meme or discuss a trope that evolves from GMO food to glyphosate, the herbicide known as RoundUp. the conversation will lead to ridiculous conclusions that Monsanto (who manufactures glyphosate) is killing everyone by forcing farmers to use RoundUp with Monsanto’s own GMO crops which are resistant to glyphosate. It’s all Monsanto all the time when discussing GMO crop pesticide use.
A new paper was published last month that may or may not give us more information about pesticide use with GMO crops.
GMO crop pesticide use – the paper
A paper, published in Science Advances by Edward D Perry et al., examined plot level choices made by soybean and corn (maize) farmers in the USA from 1998 to 2011. The results of the study were quite interesting:
- Adopters of glyphosate tolerant (GT) corn use 1.2% less herbicide than non-adopters. Evidence that GMO GT corn reduces glyphosate use.
- Adopters of GT soybeans used 28% more herbicide than non-adopters. Evidence that GMO GT soybeans great increases glyphosate use.
- Adopters of genetically engineered insect-resistant (IR) maize used 11.2% less insecticides than non-adopters. Good news for those of us who support GMO crops.
At this point, there appears a little bit of information that could be cherry-picked to support either point of view. However, it is clear that, at least for maize, GMO IR plants allow the farmer to use less insecticide to get better results. According to an NPR article,
[infobox icon=”quote-left”]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.[/infobox]
But then the results get even more complicated, and approach something I call “keep using statistics until you get the answer you want.”
Using an analytical method called environmental impact quotient (EIQ), which is a formula created to provide growers with data regarding the environmental and health impacts of their pesticide options so they can make better informed decisions regarding their pesticide selection, the authors found these results:
- Adopters of genetically modified crops used the same amount of soybean herbicides as non-adopters.
- They used about 9.8% less maize herbicides as non-adopters.
- And they used about 10.4% less of maize insecticides as non-adopters.
Using the EIQ methodology seemed to show that growing GMO soybeans show no real change in use of herbicides, whereas growing GMO maize shows the less herbicides and insecticides can be used.
Overall, I might find this article to be sufficient to make a reasonable claim that GMO crop pesticide use would be, at worst, equivalent to non-GMO crops, and at best, would require a lot less pesticide than non-GMO crops.
And that’s the end of the story, right?
But wait, there’s more
Perry et al. attempted to make a powerful comparison in use of pesticides between GMO adopters and non-adopters. Without any other consideration, this study could be a fairly important part of the discussion about the use of pesticides with GMO crops.
Unfortunately, the EIQ analytical methodology mentioned above has been deprecated because it does not take into account important factors in analyzing pesticide use. In a recent report from the National Academy of Sciences, they explicitly discourage comparing the total weight of multiple pesticides, because the total weight applied to a particular parcel of crops gives little information about toxicity, exposure, or risk.
Most researchers who investigate pesticide use for a plot of crops make use of the Environmental Protection Agency’s risk assessment or quotient system. A risk quotient (RQ) is calculated by dividing a point estimate of exposure by a point estimate of effects. In other words, it includes the estimated risk of said exposure to equation, something the EIQ does not.
This ratio is a simple, screening-level estimate that identifies high- or low-risk situations. and it incorporates the following information:
- integrates the analyses from the exposure characterization and ecological effects characterization;
- describes the uncertainties, assumptions, and strengths and limitations of the analyses; and
- synthesizes the overall conclusion about risk that is used by risk managers in making risk management decisions.
The EIQ analysis may show us that adopters of genetically modified crops used the same amount of herbicides on their soybeans as does non-adopters. But it doesn’t account for differential health risk between the herbicides used by non-adopters and adopters, a critical component to the equation.
[infobox icon=”quote-left”]…the authors based their analysis on two very flawed metrics if we want to infer anything regarding the impact of pesticide use changes. Perry et al. quantified the total weight of combined pesticides, and EIQ weighted pesticide use.[/infobox]
Neither of those metrics give us any idea of what it might mean to the farmer or the consumer.
Perry et al. do admit that the EIQ might be flawed by admitting that, “despite certain shortcomings, the EIQ’s appeal in our context is that it converts an array of attributes specific to each pesticide into a single value meant to summarize the toxicity of the chemical.” What that says to me is that they went out of their way to simplify the results. But that’s just not really good science – oversimplifying statistical analyses just to get a “cleaner” answer to a question is not what we seek in good science.
But wait, there’s even more
Perry et al. attempt to claim that there is some causality between the arrival of glyphosate resistant weeds and the use of glyphosate itself. They claim that “the estimated pattern of change in herbicide use over time is consistent with the emergence of glyphosate weed resistance.
But the oversimplified analysis, using EIQ, makes it difficult to determine if there is a causal relationship. For example, Andrew Kniss wrote a blistering condemnation of Perry et al. in his blog Weed Control Freaks:
[infobox icon=”quote-left”]Perry et al. conclude that the pattern of changes in herbicide use is consistent with the emergence of glyphosate resistance in weeds. This is certainly plausible, but it is very difficult to conclude a causal relationship.
In fact, my recent analysis of USDA data shows an increase in the number of herbicides being used in wheat and rice also, which have no glyphosate-resistant varieties. It is possible that the increase in herbicide use relates to an increase in herbicide resistant weeds in general, but I don’t think glyphosate-resistance alone can explain it. If the increases in the amount or number of herbicides used is due to glyphosate resistant weeds, why are we seeing similar increases in crops where there are no glyphosate-resistant varieties?
So although I appreciate the new methodology used in this analysis, I don’t think it provides much new information (the analysis stops at 2011) and the information it does provide isn’t all that useful. I don’t think the trends and the differences they show will be very useful from either a practical or policy perspective.[/infobox]
When all is said and done, I’m not sure this study helps in the discussion about whether GMO crop pesticide use is changed or not compared to non-GMO crops. There’s certainly no causal evidence that part of the difference in usage may be related to glyphosate or pesticide resistance.
So if you’re going to use this article as a bit of evidence that GMOs are bad, I wouldn’t do it. This article says no such a thing.
- Perry ED, Ciliberto F, Hennessy DA, Moschini G. Genetically engineered crops and pesticide use in U.S. maize and soybeans. Sci Adv. 2016 Aug 31;2(8):e1600850. doi: 10.1126/sciadv.1600850. eCollection 2016 Aug. PubMed PMID: 27652335; PubMed Central PMCID: PMC5020710.
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