About those harsher herbicides that glyphosate helped replace:

One of the common criticisms of commercially available Genetically Engineered (GE) seeds is the idea that they have led to an increase in pesticide use. In actuality, it turns out that they’ve corresponded to a decrease in total pesticide use, but this is attributable primarily to insect resistant GE crops, and critics argue that herbicide resistant crops have led to an increase in herbicide usage. It is true that the rise in popularity of glyphosate-resistant (GR) crops in particular has coincided with an increase in the use of glyphosate, which had already been in use to some degree for a couple of decades before the implementation of glyphosate-resistant crops. However, what critics invariably fail to mention is that its rise in popularity also coincided with the phasing out of other herbicides, most of which were significantly more toxic than glyphosate (about which I’ve written in detail here).

The purpose of this article is not to claim that glyphosate and GR crops are the be all end all of weed control (they’re not), nor is it to claim that they were causally responsible for any and every desirable change we see in herbicide usages patterns. Rather, the purpose of this is to show that when opponents of GE technology and of glyphosate claim that GR crops are bad on the grounds that they increased glyphosate use, they are leaving out critical information that would be highly inconvenient for their narrative.

It’s important to note that the data upon which these usage timeline graphs are based is very USA-centric. Perhaps a timeline and analysis of herbicide usage patterns in other places would be a good topic for another article, but the US is not a bad place to start because we do cultivate a lot of glyphosate-resistant crops here, as well as a lot of GE crops in general.

What were some of these herbicides?

Alachlor was one of them. The EPA states the following about alachlor:

“The greatest use of alachlor is  as a herbicide for control of annual grasses and broadleaf weeds in crops, primarily on corn, sorghum and soybeans.”

Alachlor use

Alachlor: [Source]

According to the EPA’s Water division:

“Some people who drink water containing alachlor well in excess of the maximum contaminant level (MCL) for many years could have problems with their eyes, liver, kidneys, or spleen, or experience anemia, and may have increased risk of getting cancer.”

The EPA and OSHA list alachlor as a Class L1 Carcinogen, which means they consider it likely to be carcinogenic at high doses but not at low doses. With an LD50 of between 930 mg/kg and 1,350 mg/kg in rats, and between 1,910 and 2,310 mg/kg in mice, its acute toxicity is not generally considered to be a big concern (although you may notice that it is still noticeably more acutely toxic than glyphosate which has an LD50 of 5,600 mg/kg). However, its potential for chronic toxicity remains a concern, particularly for the liver, spleen and kidneys (according to its PMEP profile) , and its NOAEL varied depending on the duration of the study in question.

Okay then. What else? How about Cyanazine?

Cyanazine use dropped to zero

Cyanazine use dropped to zero shortly after the rise of GR crops.

Cyanazine has an LD50 of between 182 and 332 mg/kg in rats and 380 mg/kg in mice (far more acutely toxic than glyphosate or alachlor), but its long term effects and NOAEL varied from anywhere around 0.198 to 3.3 mg/kg depending on which study you look at (as you may read more about in this WHO report). Although cyanazine is not known to be carcinogenic for certain, it has been observed to affect the central nervous system upon over-exposure and to increase liver weight while decreasing body weight gain.

Cyanazine was eventually put under special review due to concerns over its possible cancer-causing potential. DuPont voluntarily discontinued it in 1999, and its sale in the US was officially prohibited by 2002.

So, needless to say, cyanazine use went way down rather abruptly. What else?  According to PMEP, Fluazifop “is a selective phenoxy herbicide used for postemergence control of annual and perennial grass weeds. It is used on soybeans and other broad-leaved crops such as carrots, spinach, potatoes, and ornamentals.”

Fluazifop usage

Fluazifop usage

Fluazifop hasn’t gone away completely, but its use did decline quite significantly, possibly thanks in part to the introduction of glyphosate resistant soybeans. How toxic is it though? its LD50 was 3,680 for male rats and 2,451 for female rats, which is only a little bit more acutely toxic than glyphosate, but PMEP notes the following:

“A single dose of the formulated compound (Fusilade 2000) can cause severe stomach and intestine disturbance. Ingestion of large quantities may cause problems in the central nervous system such as drowsiness, dizziness, loss of coordination and fatigue. Breathing small amounts of the product may cause vomiting and severe lung congestion. This may ultimately lead to labored breathing, coma and death.”

So, yeah. There’s that. The good news is that there was no evidence of chronic toxicity in rats under 10 mg/kg per day in 90 day trials.

The next one up is metolachlor.

Technical grade Metolachlor has an LD50 of between 1,200-2780 mg/kg in rats. That’s between twice and 4.67 times the acute toxicity of glyphosate. Additionally, with an NOAEL of roughly 90 mg/kg/day, metolachlor can exhibit chronic toxic effects at doses MUCH smaller than the levels at which it becomes acutely toxic. Symptoms of  human intoxication from metolachlor include abdominal cramps, anemia, shortness of breath, dark urine, convulsions, diarrhea, jaundice, weakness, nausea, sweating, and dizziness.

Okay. Great, but what about Atrazine? In 1996 Atrazine was the #1 herbicide for corn. 2 and 3 were cyanazine and alachalor which, as we just saw, have effectively been zeroed out.

Well, apparently the rise of GR crops has had little to no effect on atrazine usage in the US. This might come as both a surprise and a disappointment to some because atrazine is known to degrade very slowly in soil (often lasting for months) and  has been known to inadvertently end up in drinking water, a fact which contributed to it being banned in the EU. It’s also a suspected endocrine disruptor and is more acutely toxic than glyphosate (with an LD50 of 672 to 3,000 mg/kg in rats). The EPA also classified it as a possible carcinogen, and multiple undesirable biochemical and morphological changes in various organs have been observed in high dose studies of its chronic toxicity. That’s probably not what most of my readers wanted to hear. However, part of being a responsible skeptic is understanding the importance of not cherry picking data. Additionally, we may be able to learn something by asking why this is the case. While at first glance this result is not so exciting, bear in mind that resistant weeds have increased quite a bit without increasing use AND corn production is greatly increased (by about 54%) since 1996, so use per bushel is down (as is use per capita because the population is up in the US by about 50 million people since then). Alright then. That’s not as spectacular as those previous examples, but at least it wasn’t a total bust.

What else? How about Metribuzin?

In 1992, over 2.5 million lbs of metribuzin was used just on soybeans alone. After that, its usage on fruits and vegetables didn’t change too drastically, but we can see that its use on soybeans and its overall use dropped dramatically. It eventually started climbing back up, and there a number of possible reasons for that, but it did initially go down, particularly in soybeans (for which a glyphosate-resistant variety was introduced by Monsanto in 1996). Metribuzin’s LD50 is 1,090 to 2,300 mg/kg in rats, which is about 2.5 to 5 times as toxic as glyphosate. None of the studies looking at chronic toxicity revealed any negative effects at any of the dosages tested.

Another one that was popular in the mid 90s in the US was Nicosulfuron.

Nicosulfuron usage

Nicosulfuron usage

The acute toxicity of Nicosulfuron is not much worse than glyphosate, with an estimated LD50 of in excess of 5,000 mg/kg of body mass. As for chronic toxicity, its NOAEL was found to be about 125 mg/kg/day, and its LOAEL (Lowest Observed Adverse Effect Limit) was found to be 500 mg/kg/day according to the EPA.

If you’ve made it this far, you may be wondering how this data was obtained. The website was created by USGS National Water Quality Assessment (NAWQA) Program.

“The pesticide-use maps provided on this web site show the geographic distribution of estimated use on agricultural land in the conterminous United States for numerous pesticides (active ingredients). Maps were created by allocating county-level use estimates to agricultural land within each county. A graph accompanies each map, which shows annual national use by major crop for the mapped pesticide for each year.

Methods for generating county-level pesticide use estimates are described in Estimation of Annual Agricultural Pesticide Use for Counties of the Conterminous United States, 1992–2009 (Thelin and Stone, 2013) and Estimated Annual Agricultural Pesticide Use for Counties of the Conterminous United States, 2008-12 (Baker and Stone, 2015).  Two different methods, EPest-low and EPest-high, were used to estimate a range of use, with the exception of estimates for California, which were taken from annual Department of Pesticide Regulation Pesticide Use Reports (Baker and Stone, 2015).”

A PDF copy of the entire Thelin and Stone report can be found here, but their quick summary of the data sources is as follows:

“Data sources used to develop EPest pesticide-by-crop use rates and annual pesticide-use estimates by county included the following: (1) proprietary pesticide-by-crop use estimates reported for CRDs; (2) USDA county harvestedcrop acreage reported in the 1992, 1997, 2002, and 2007 Census of Agriculture (http://www.agcensus.usda.gov/), and NASS annual harvested-crop acreage data collected from crop surveys for non-census years (http://quickstats.nass.usda. gov/); (3) boundaries for CRDs and counties; (4) regional boundaries derived from USDA Farm Resource Regions; and (5) pesticide-use information from California DPR-PUR. Each of these sources is described in following sections.”

The USGS also includes this statement on the strengths and limitations of the data:

“Pesticide use estimates from this study are suitable for making national, regional, and watershed assessments of annual pesticide use, however the reliability of estimates generally decreases with scale.  For example, detailed interpretation of use intensity distribution within a county is not an appropriate use.  Although county-level estimates were used to create the maps and are provided in the dataset, it is important to understand that surveyed pesticide-by-crop use was not available for all CRDs and, therefore, extrapolation methods were used to estimate pesticide use for some counties. Surveyed pesticide-by-crop use may not reflect all agricultural use on all crops grown. In addition, state-based restrictions on pesticide use were not incorporated into EPest-high or EPest-low estimates. EPest-low estimates are more likely to reflect these restrictions than EPest-high estimates. With these caveats in mind, including other details discussed in Thelin and Stone (2013) and Baker and Stone (2015), the maps, graphs, and associated county-level use data are critical data for water-quality models and provide a comprehensive graphical overview of the geographic distribution and trends in agricultural use in the conterminous United States.”

Many people never even hear about the herbicides that were phased out in favor of glyphosate simply because they aren’t pertinent to the anti-agricultural biotech narrative, and because their popularity had waned by the time it had become trendy to demonize GMOs and everything remotely associated with them.

I said this before, and I’ll say it again:

“Opponents of glyphosate often seem to hold this unfounded notion that, if they can manage to get glyphosate banned or simply willingly abandoned, then it would mean an improvement in both food and environmental safety, but the truth is it would likely be the exact opposite of that. Weeds are a legitimate problem in farming that has to be dealt with one way or another. In its absence, it would have to be replaced with something else, and it would likely be something more caustic: not less.”


– Credible Hulk.

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  1. I think (ie:no evidence) atrizine usage hasn’t dropped because there is still amount of conventional corn grown (rr sweet corn was just released in 2014 I believe). Also, there may be some people mixing it in with round up to fight/prevent glyphosate resistance.

    • Ironically mixing atrazine (a Class C herbicide in Australia) with glyphosate (a Class M herbicide) increases resistance to both. Alternating use is superior for preventing resistance.

      • I believe the work this team of exrpets have done is amazing. Finally some of the truth about GMO foods is being uncovered. It is a shame that the FDA, the USDA and the EPA won’t sit up and pay attention. A 90 day study is not long enough! This team did a 2 year study and found some disturbing data related to genetically engineered foods and its effects on our body. Keep up the good work! And thank you

  2. A good addition to this article would be the standard application amounts for each of the herbicides as compared to the LD50. Most people have no idea of the tiny amounts of herbicide actually used due to dilution with water. LD50 is good, but without an idea of how much is actually applied to get the herbicide effect, it’s not that informative.

    • That’s a good idea. I’ve gone over the EPA tolerances and how the RFDs were arrived out via the No Observable Adverse Effect Limit (NOAEL) from chronic toxicity studies with respect to glyphosate, but I haven’t done the same for any of these other ones. That would be a nice reference for people to have.

      • Yes, most is diluted with 1000 gallons of water. A rate per acres of most of these is in ounces. ie atrazine is half pint per acres. Metribuzin on soybeans rate is 2 oz way early before the beans are even up. and yes, you are correct….now we are going back to the witches brews of the 1990s because of the demand for more “conventional” crops. That or grab by hoe, and I dont feel like walking up and down the “yardlines”(rows) of 4500 football fields. LOL.

      • Sarah Christie

        Yes please – I’ve been asked about that a number of times. A real measure of the relative toxicity of pesticides involves the amount applied as well as the LD50, and I’ve not yet found anything combining these two. So when I point out that glyphasate is far less toxic than x and somebody says “yes but much of it gets put on the plants in comparision to x”, I don’t have a answer. Cheers.

        • I’ve been looking for similar data on pesticide usage, alternatives to glyphosate, etc., and I did come up with this, which at least goes over suggested usage/amounts and efficacy on different pests for Atrazine vs. Roundup(glyphosate), Gramoxone and Banvel. It’s a start, I guess…

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  6. Surprised you didnt discuss diquat/paraquat usage. That stuff is horrid, and glyphosate all but replaced it. Now we’re starting to use diquat/paraquat again because it still works.

    • According to the water.usg timeline data, neither one really went down all that much.
      I suppose It wouldn’t have hurt to have included them anyway though.


    • In Australia they’re used in tandem as a “double knock” strategy. Fields are sprayed with glyphosate, any resistant survivors are then sprayed with paraquat. Best part is it takes effect immediately, bad news is a tiny dose is often lethal. A farmer in our district died a few years back when his backpack sprayer cracked and he ended up splashed in the face with the stuff.

  7. A quick comment on your metolachlor section. The main reason there was a drastic drop in the use of this herbicide was that it was replaced with S-metolachlor. There are several different isomers of metolachlor, and the S-isomers are more active than the R-isomers. So the newer formulations contain mostly S-metolachlor (active form) and were released in 1998, around the time metolachlor dropped. You have to use less S-metolachlor compared to metolachlor because it is more active, so the use rate dropped. To get the full picture, you should look at the USGS figure for S-metolachlor here: http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=2012&map=METOLACHLORS&hilo=L&disp=Metolachlor-S

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  9. Undoubtedly you know that the affect of herbicides must take into account how fungi are affected. Plants are scaffolds for microfungi. Both then affect pollinators and other consumers, not to mention their internal flora. Going forward, I hope to see more germane discussion from the literature attempting to detangle this mess further.

  10. It would be interesting to post up the glyphosate usage over time for comparison. Does the increased amount of glyphosate used outweigh the decreased amount of other herbicides?

    Along those lines, how does glyphosate synthesis compare to synthesis of the other herbicides? Is glyphosate synthesis a “dirtier” process (i.e. does it generate more toxic waste, pollution)?

    • I too am curious about this comparison. Would it not have been just as easy to include the glyphosate graph that was nonchalantly linked to in the article, from the same source as the rest of the graphs. I took a quick look and it would appear that the peak of the glyphosate graph (the most recent year of use, oddly enough) was pushing 300 million lbs used while the peaks of the rest of the graphs that were included in the article combined would hardly be close to even half of that.

      • It was not germane to the point of the article. Nobody disputes the fact that glyphosate usage has increased. The point is that the total toxicity of food has decreased, and comparing the total weight of a given herbicide used with another is not a valid measure of that. They have different LD50s, different NOAELs and the total amount of food being produced has increased. What you’re bringing up is precisely one of the misleading half-truths to which this article is a response.

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  25. No any doubts whoeeasvtr that GM foods change animal, including human, cells to a state they turn to cancerous over time. So all the Monsanto’s and other biotech companies tricky games are based on cancer tumors growing slowly in long-lived species like human, so it can take some 10-20 years of a cancer tumor to grow in human. Meanwhile, Monsanto is in a hurry to make another number of billions of dollars on selling unlabeled-as-the-GMO carcinogenic GM foods, such as every single chocolate bar and candy with lecithin in it from GMO soy, corn-muffins and a number of brands of corn chips and popcorns, or every single can or bottle of soda with GMO corn syrup, and every condiment, or dressing with it, and many Mexican dishes based on GM corn flour and corn oil, or GMO Canola and Soy oil most frequently used in any restaurant’s cuisine/dishes. GMO are in every single piece of your farmed fish, and meat, and egg, and cheese for a number of years, since the fish and cow are fed GMO soy and GMO corn in our country DAILY.This is the main cause of your and your kids health problems and the monsterous obesity in the country.So if we do not start educating ourselves on GMO and do not demand our government now to stop pretending that they have no idea about what is going on with the notorious biotech industry, which is exterminating the US citizens as they do with their masterpieces super-weeds or super-bugs, then your kids and your grandchildren lives are in the greatest danger ever in the entire history of the planet Earth.

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  29. Very interesting data, good article, thanks. It doesn’t, however, take into account changes in the amount of crop cultivated over time.

    What would make it more interesting though is to combine it with historic cultivation data to get a rate of pesticides sprayed per-acre. When we discuss GMOs and pesticide use, the per-acre use is probably what we are thinking of.

    Well… actually the pesticide use over farm yield might be an even better metric.

    • Those are relevant considerations. That’s why I mentioned them in the atrazine section. Given that per/hectare yields have improved for many types of crops, it probably would even further strengthen the argument that food safety has improved, at least insofar as total pesticide exposure and toxicity is concerned.

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  36. Glyphosate’s molecular weight is 169 and it is a competitive inhibitor, which is the same mode of action as LSD, meaning that it’s like a lock in a key, and therefore small masses of the small molecule does a lot.

    Therefore, it’s not reasonable to compare pesticides by weight or mass. It makes sense to speak qualitatively, and to describe quantities with the caveat that it’s apples and oranges.

    Glyphosate’s a special case with special risks and benefits. It’s by no mean guaranteed to be safe and there is continuing debate on the safety in regard to a few modes of action.

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  55. is that final sentence supposed to be a some kind of good argument?
    its a vague assumption that if gyphosate was banned, then something worse would replace it?
    thats not very convincing, and of course its just speculation, of course what we actually need to do, is stop using synthetic pesticide, and stop farming animals, which is unhealthy and unsustainable (and an excuse for gmo) and start growing food for humans, in an organic way.

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