The Promise of GMOs: Herbicides

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GUEST AUTHOR:  | @geneticmaize | On Facebook: Anastasia Bodnar: Science Communicator

Anastasia is Policy Director of Biology Fortified, Inc. and the Co-Executive Editor of the Biofortified Blog. She has a PhD in genetics with a minor in sustainable agriculture from Iowa State University. Her favourite produce is artichokes!

[ A version of this essay previously appeared on Biofortified. ]


This is a part of the series The Promise of GMOs. Do GMOs live up to the promises of the biotech industry? In the case of decreasing herbicide use and improving the environmental impact, there is data to back up industry claims.

Reducing herbicide use

Data from the EPA.
Data from the EPA.

BIO’s claims here are that “Biotech is helping to feed the world by: Lowering volumes of agricultural chemicals required by crops-limiting the run-off of these products into the environment [and] Using biotech crops that need fewer applications of pesticides.”

Verdict: Promise met (for herbicides specifically, insecticides will be covered in another post).

Looking at the most up to date EPA data on agricultural pesticide use, we see that use of herbicides, insecticides, fungicides, and other conventional pesticides (such as miticides) all have a downward trend between 1998 and 2007. The slopes of the linear trendlines are in the legend of the chart to the right. Strangely, other pesticidal substances (such as sulphur, petroleum, and other chemicals used as pesticides) has a strong upward trend, which caused the total to increase. If you were to look at just the total, you wouldn’t get the overall picture.

This dataset from the EPA includes “one from the USDA and others from private pesticide marketing research companies”. I wish there was more recent data, but this is what we have to work with. If you extrapolate into the future without adequate data you might not get the right picture. Brookes and Barfoot have published results from slightly more recent datasets (such as an herbicide use decrease of 75 million lbs [PDF] from 1996 to 2010) but since part of the dataset is proprietary and I couldn’t look at it, I didn’t feel comfortable using it here.

So we know that herbicide use seems to be decreasing at the same time that GM crops increased. But is that correlation or causation? And is total herbicides even the right way to look at this?

Let’s turn again to the USDA and EPA researchers in their Conservation Tillage, Herbicide Use, and Genetically Engineered Crops in the United States: The Case of Soybeans (paraphrased):

Most researchers measure herbicide use by the total pounds of active ingredients applied. While this is informative, these of these studies can be biased by unobservable conditions prevailing in the year of the study. Also, when different types of active ingredients are grouped together, it covers up the fact that their characteristics (potency, toxicity, etc.) vary widely.

Therefore, any studies that look at volume or mass of herbicides is not telling the whole story. So the small decrease in herbicide use shown above may not be relevant if there was a switch to much more toxic herbicides. They continue (paraphrased):

Some studies suggest that herbicide use on HT soybeans may be slightly higher than herbicide use on conventionally grown soybeans in the United States. However, glyphosate (the herbicide used on most HT crops) is less toxic to humans and not as likely to persist in the environment as the herbicides it replaces. Consequently, increased herbicide use on HT soybeans is not necessarily indicative of worse environmental outcomes.

Data from Fernandez-Cornejo et al, 2012.
Data from Fernandez-Cornejo et al, 2012.

The table to the right summarises herbicide use on soybeans in 1996 before HT crops were widely adopted, and in 2006, after HT crops were widely adopted. The data is again from Conservation Tillage, Herbicide Use, and Genetically Engineered Crops in the United States: The Case of Soybeans.

For the column headings, Use = % of this pesticide compared to the total of all pesticides; Rate = pounds of active ingredient applied per acre of soybeans; Toxicity = chronic toxicity score (higher is safer); and Half life = number of days it takes for 1/2 of the herbicide active ingredient to degrade in the soil.

I added the EIQ (Environmental Impact Quotient, lower is safer) for each herbicide because I’m not familiar with the chronic toxicity score. EIQ is a numerical representation of the risks a pesticide poses for the environment, consumers, and farm workers. The EIQ for 2,4-D is an average of the EIQs for 5 different formulations of the herbicide.

In 1996, soybean farmers were using a variety of pesticides, and at least 68% of herbicides used had toxicity scores that were worse than glyphosate. In 2006, the majority of farmers had switched to glyphosate, the least toxic of the bunch, making up 85% of herbicide use.

The total amount of herbicides is trending down and the total environmental impact due to herbicides has decreased. While we can’t be sure if HT crops were the cause of the total decrease in herbicide use, we can be reasonably certain the change in herbicide types was due to HT crops. So, the verdict for BIO’s claim is: promise met. However BIO’s use of “volumes” in their claim specifically is a poor measure for pesticides, it makes much more sense to look at the types of herbicides.

Disclaimer: Anastasia’s words are her own and views expressed do not necessarily represent the views of her employer. She is not paid to blog or conduct any social media activities. Mention of a company or product does not indicate endorsement.

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3 Comments

  1. Now, for one thing, i do think reduction of other herbicides is a good thing, and glyphosate is not as extremely toxic as some other herbicides, but not all the data is in, either. Industry science is biased and doesn’t check things that a conscientious entity would check for safety like probable disruption of gut microbiota on chronic exposure. The track record of research is shady, too, with early Monsanto feeding trials unpublished and with signs of doctoring of data in early EPA memos from 1985, 1986, and 1991. And there is quite the propaganda machine supporting the product sort of like climate change denialism supports fossil fuels. All these things together are not ideal. Probably better than other herbicides used before the Roundup Ready product combo, but not all above board still. The 1991 EPA memo is especially shady and the 200 and 2015 review articles on safety are also clearly biased. Three of the EPA staff refused to sign the 1991 memo, and nobody has investigated why, but it’s obvious on a cursory examination that there is agenda pushing in that document.

    Lastly, FAFDL excludes people like me from the discussion forum intentionally because they say i’d be a time-sink but it’s really more because i don’t serve the party line so well.

    • False. Glyphosate has been studied way more than most other substances because of urban green politics. It is remarkably safe and we know this because of the good health of farmers who use glyphosate in the 19,000 participant US Ag Health Survey, which has been running for 20 years. These farmers live considerably longer and healthier lives than the average American.

      A far bigger health issue is the broken backs and arthritis and poverty of workers in the organic industry. Does anyone remember how the Cali organic industry gained an exemption from the ban on the short handled hoe, a device that is essentially an instrument of torture that cripples workers backs?

      As I say, this is about urban green politics and these people do not care about worker or consumer health, they only care about convincing consumers to buy high profit margin organic food so they can live high on the hog.

    • No, you are excluded from discussions because you are unrealistic, a conspiracy theorist, irrational, unscientific and an irrepressible fockwit internet troll who has nothing substantive to contribute. Other than that, you’d make a wonderful participant.

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