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There’s more of a difference between a crop and a weed than where they grow

In reading the coverage of the transgenes in canola story, two ideas continue to come up that bother be because they’re just plain wrong. I don’t have exact citations for these, but I’ve seen both concepts repeated multiple times on multiple sites.

1. “What’s a crop growing outside of the field where it’s planted? A weed that’s what!”


Succeeding as a crop species and succeeding as a weed both call for a great deal of biological specialization, and maybe of the requirements are mutually contradictory. Let’s touch on a single example. Seeds. In general crop species are going to have small numbers of large seeds that don’t disperse very well. A soybean pod will generally contain 3-5 seeds. An ear of corn might hold 200 kernels. Neither plant has an effective method distributing its seeds other than human intervention and all the seeds germinate when they’re planted, they don’t lay dormant in the soil for years. Compare that to one of the pernicious weeds farmers actually might worry about Pennsylvania smartweed (Polygonum pensylvanicum). A single smartweed plant can produce an average of 19.500 seeds!* The seeds lie can dormant in the soil for years so that even if not a single smartweed survives to flower and produce new seeds it can take more than a decade for new seeds to stop germinating each spring. Source for the smartweed statistics.

Now canola isn’t quite as dependent on humans as core crops like grains or potatoes. The average canola plant produces 900-3500 seeds. However those seeds will still germinate in one year, they don’t have the patience to wait for years for the perfect opportunity like many weed species, and like corn or soybeans, canola lacks an effective method to distribute its seeds other than relying on human hands. To make this point, let’s turn to the study itself (as quoted by the International Business Times):

… much of the population of modified plants was found near canola processing facilities or along roads near where trucks stop, indicating that falling off the trucks during delivery is a likely source of the seeds.

Canola in itself is not a very competitive plant – it doesn’t invade areas the way that water hyacinth or kudzu has in the American south. “This isn’t the alien plant that eats your poodle,” Sagers [one of the authors of the study itself] said.

2. “Now that canola is interbreeding, it can’t be long before it breeds with other weeds and they’re carrying the transgene!”

Is gene flow to wild species that do possess the characteristics to be problematic weeds a valid concern? Maybe. I don’t know if any close relatives of canola are, in fact, pernicious weeds. But assuming such weeds exist, and they grow in the same places that genetically engineered canola is planted, there could be some level of risk that the gene for herbicide resistance could end up in those populations. Still it seems silly to worry about that right NOW!

Here’s why:

  • There’s a big difference between reproducing within a species and producing fertile hybrids with a separate species. That’s the whole point of the species concept. If you can reproduce together you’re one species. If you’re not one species you either can’t reproduce together or your offspring aren’t viable (they’re sick, sterile, etc) the point is genes can flow freely within a species, not so much between species. Now plants, being generally awesome, are better at producing fertile hybrids between different species than animals are, so there’s some possibility of gene flow when you grow crops in close proximity to related wild species but that takes me to my second point!
  • That risk already existed. Whatever wild species grow near canola fields have been exposed to the pollen of canola plants carrying herbicide resistance genes since farmers started planting them. Is there any reason canola plants growing on the side of the road are MORE likely to successfully reproduce with a related wild species than the plants growing in a farmer’s field? Now maybe you already think we shouldn’t be growing genetically engineered crops for exactly that reason. I happen to disagree with you, but the findings of this report don’t make gene flow to wild species any more likely than it already was!**

*If those seeds were the size of corn kernels, that single plant would produce ~16 pounds of seeds, but of course they’re actually much smaller.

**If I’m wrong on this point, someone please enlighten me.

5 Comments

  1. But you don’t understand — they’re superweeds! SUPERWEEDS, man! We have no choice but to panic!

    The issue that’s been getting me the most upset about this whole thing is that none of the alarmists have bothered to give me a reason why I should give a crap. So this canola can withstand certain herbicides, and it spreads. Big whoop. We’re cultivating it on purpose already: we’re supposed to want there to be more of it, right?

    And anyway, all this is likely to do is make the particular herbicides in question less effective. If they’re not as effective, then we’ll stop using them so much.

    If we stop using the herbicides as much, then these plants lose their advantage over other plants.

    If these plants lose their advantage over other plants, then they’ll be outcompeted and will eventually disappear. Problem solves itself.

    I’m willing to be mildly upset about stuff like BT corn (most of what I’ve seen suggests that it’s not especially dangerous to monarchs and other nontarget organisms, but there’s still the issue of Monsanto ruining a public good, and the possibility that the transgenes in question might become more of a threat to nontarget organisms. But one doesn’t have to freak out over every transgene regardless of its origin or purpose. This one looks to me like it’s more likely to hurt the companies that sell the herbicides than anybody else, and I’m pretty okay with that, frankly.

    1. James says:

      It does end up kind of circular. Why do they think herbicide resistance GMOs bad? Because they arguably increase the spraying of herbicides. Why is it bad if the trait escapes into weedy species (or weeds develop their own resistance)? Because then we won’t be able to use those herbicides as much.

      I could understand, if not agree, with a person worried about one of those things, but being worried about both at once strains credibility.

      1. Greg says:

        Even with resistance genes mating with a crop is a bad move for any would be weed. Especially for the reasons you’ve mentioned above.

  2. There’s also the matter of weeds being able to spontaneously resist herbicides, with or without any GMO canola. As much Round-Up (glyphosate) as gets sprayed around, I’d have been surprised if some weeds didn’t figure it out on their own sooner or later. Everybody’s acting like glyphosate was going to be some kind of miracle herbicide that was going to be useful forever. This whole story makes me mad.

  3. John Walter says:

    Very good discussion on a topic of interest to many of our magazine readers and website visitors. We’re featuring your blog today on the Agriculture.com [A]-List. It deserves a wide airing among agriculturalists, including farmers.

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