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Super-weeds?

Long time readers will know I have serious problems with using the term superweeds to describe weeds that have resistant to a herbicide. Yes, herbicide resistant weeds are a serious issue (just like antibiotic resistant diseases), but they are ONLY a problem for people who use the herbicide in the first place. A nytimes article from a few days ago on herbicide resistant weeds, while earning a little of my ire for still calling them superweeds, makes this point amazingly concisely:

The National Research Council, which advises the federal government on scientific matters, sounded its own warning last month, saying that the emergence of resistant weeds jeopardized the substantial benefits that genetically engineered crops were providing to farmers and the environment.

The danger, if we don’t do a better job of managing resistant weeds (through strategies ranging from crop rotation to developing crops resistant to different herbicides to allow farmers to rotate between different herbicides) is that we will lose some of the environmental benefits genetic engineering is ALREADY providing. Farmers who don’t use crops genetically engineered to resist herbicides, whether they grow their crops conventionally (using other herbicides, plowing, or hand weeding to control crops) can deal just as well — or as poorly — with giant pigweeds* that are “superweeds”, as those which are not.

*Which the nytimes informs us can grow 3 inches a day under ideal conditions. In other news, that’s pretty awesome! Corn might be able to beat it unless the pigweed got a head start**, but weeds are a much more serious issue for crops like cotton and soybeans which don’t ever get as far up off the ground.

**This is entirely my own amature speculation, I’ve never had to grow corn in a production environment and the last time I was responsible for a real field of research corn, we controlled weeds the old fashioned way (long days in the sun with a hoe***) until the corn plants got big enough to hold their own.

***Everyone should really spend at least one day hoeing corn (or some other crop, I’m not particular). For a little while it’s fun and exhilarating, and by the end of the day you have a much better understanding of why very few people would ever CHOOSE a life of manual agricultural labor, whether as subsistence farmers or migrant laborers.****

****Sorry for going so crazy with nested foot-notes. Clearly I’ve been missing this style of writing more than I realized!

7 Comments

  1. […] just published something relevant to this somewhat sterile debate, though in response to the “superweed” story in the NY Times that’s been going viral rather than in direct response to […]

  2. […] just published something relevant to this somewhat sterile debate, though in response to the “superweed” story in the NY Times that’s been going viral rather than in direct response to […]

  3. Sanjuro says:

    Presumably the weed resistance is due to old fashioned artificial selection (i.e. heavy use of Roundup created heavy selection for resistance in weeds). However, as spectacularly unlikely as it probably is, it would sure be interesting to see if the resistance genes from GM crops have somehow introgressed into the weeds. It should be a pretty easy PCR experiment. I’m assuming it is unlikely because I’m assuming the weeds in question are not closely related enough to the GM crops to interbreed. Have they found the genetic basis for the weed resistance yet? (I should probably look for myself but I’m being lazy).

    By the way, great blog James, I’ve enjoyed reading it for a while now.

    Sanjuro

    1. James says:

      I’m glad to hear you like the site!

      To answer your question about the mechanism of resistance to roundup. I know researchers have looked at how resistance has developed in a number of weed species. The paper I know off the top of my head looked specifically at glyphosate-resistant pigweed and found that the species has simply increased the number of copies of the gene targeted by the herbicide to up to a 100 copies spread throughout the genome. The plants just so much of the target protein (5-enolpyruvylshikimate-3-phosphate synthase or EPSPS) that no matter how much of it is disabled by herbicide, the plant can survive. Here’s the paper if you’re interested. In the introduction them mention that some other weeds have either gotten better at pumping glyphosate out of their cells before it can do enough damage, or have developed changes to the EPSPS enzyme itself that keep the herbicide from properly interacting with it (but I haven’t read those papers myself).

      The selective pressure weeds have been under to develop SOME form of resistance has been huge, and even though the potential repercussions are worrying, it’s a fascinating to learn about the different paths different species have taken to develop that resistance.

  4. Ford says:

    Herbicide resistance is indeed only a problem for people who use herbicides, but that includes many people who don’t grow herbicide-resistant crops. Vegetable crop growers, for example, don’t have herbicide-resistant varieties, so they don’t spray glyphosate (for example) ON THEIR CROPS. But many still use it to control weeds during fallow periods, to keep weeds from shorting out electric fences, etc. Once the crops are up, they switch to mechanical cultivation, etc. Similarly, organic farmers have used Bt spray, even though they don’t grow Bt crops. In both cases, transgenic crops have sped the evolution of resistance to useful chemicals, by increasing reliance on a single weed/pest control measure, thereby increasing the intensity of selection for resistance.

    This is not intended as a generic argument against transgenic crops, but as an argument for taking resistance management more seriously.

    1. James says:

      That’s a very valid point Ford. I definitely keep it in mind when I think about bt resistance, but I guess I hadn’t thought about it as much with broad spectrum herbicides like glyphosate, although now that you mention it I completely agree it’s a concern.

      (Sorry it took so long to post your comment! My spam filter has been getting out of control again recently)

  5. […] had the yellow sun of earth, spiderman had a radioactive spider-bite, but what about superweeds, where does their super power (surviving application of Round-up/glyphosate) come […]

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