Monsanto advices framers to use three additional herbicides to deal with herbicide resistant palmer amaranth. What happened to the promise that GM crops would reduce the herbicide applications? Is this the confirmation that such promises were just a sales pitch?
Monsanto and scientists from the University of Georgia have determined that Palmer amaranth (pigweed, Amaranthus palmeri) at specific sites is resistant to glyphosate, the active ingredient in Monsanto's Roundup herbicides – just as another seven weed species registered at weedscience. About 200 hectares (500 acre) of Bt cotton in central Georgia (US) are infested with the herbicide resistant weed.
Monsanto's solution: Just apply another three herbicides before, during and after RR cotton cultivation, as well as additional herbicides for weeds growing outside the fields.
"Monsanto recommends that farmers growing Roundup Ready cotton or Roundup Ready Flex(R) cotton who have glyphosate-resistant Palmer amaranth on their farm do the following for 2006:
* Use a pre-emergence residual herbicide such as Prowl
* Apply Roundup agricultural herbicide plus metolachlor early post-emergence
* Apply Roundup agricultural herbicide plus diuron at lay-by.”
Monsanto press release, 13 Sep 2005
How about a different solution? Resistance to a specific herbicide can be solved by not using that herbicide, by applying other (conventional or organic) practices such as tillage. Unfortunately, this weed is apparently very hard to deal with with other herbicides once it is taller then 15 cm, so herbicided-based alternatives are few. And of course not applying Roundup, would make the GM herbicide tolerance of Roundup Ready (RR) cotton pointless. So, farmers will end up doing both: using Roundup as well as the older herbicides that RR crops were supposed to replace. Yet another solution would be not to grow RR cotton anymore.
Unfortunately the problem goes beyond those 200 hectares where the herbicide resistant crop was found.
Everybody using RR crops and who might have Palmer Amaranth is asked by Monsanto to use an additional herbicide just to be sure. And of course is also applies for farmers growing RR maize and RR soybeans because they use the same herbicide.
So far, as expected. But to make things not sound as bad, Monsanto starts argues that it is actually good to have an additional pre-emergence residual herbicide.
According to Monsanto's Roundup Technical Manager: "Using a residual helps reduce early season weed competition and reduces the number and size of weeds when the first application of Roundup is made."
Does anybody remember the promises why herbicide tolerant crops such would reduce the amount of herbicides? That it wouldn’t be necessary to spray before the weeds are already grown a bit? That this would mean less herbicide applications? An now Monsanto tells us that it’s actually better if the weeds are treated with another herbicide first?
The list of herbicide resistant weeds is growing, so complementing RR crops with additional herbicides is likely to become the norm not the exception, especially when one takes into account that herbicide resistant weeds can affect all field with RR crops – that is the combined acreage of maize, canola, cotton, soybeans and every other RR crop. For Liberty Link maize in North America, the complementary herbicide glufosinate is already sold together atrazine as pre-emergence residual herbicide, so we should keep our eyes open for the introduction of combined herbicide packages for RR crops as well.
For a list of registered herbicide resistant feeds check www.weedscience.com
Update, 26.9.2005: Just a few weeks after the herbicide resistance of Palmer pigweed was confirmed, another pigweed had to be added to the list: common waterhemp. The resistant populations were found in Monsanto's home state Missouri in the US.
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