Monday, May 10, 2010

On herbicide resistent weeds

In view of Activists voice concerns over Biotech Regulatory Authority Bill:
“whoever, without any evidence or scientific record misleads the public about the safety of organisms and products…shall be punished with imprisonment for a term which shall not be less than six months but which may extend to one year and with fine which may extend to two lakh rupees or with both”, it may be good to have some 'scientific' information though there are some concerns Do Seed Companies Control GM Crop Research?.
International Survey of Herbicide Resistent Weeds has a list of weeds, suggested action and some downloadable books.
Glenn Davis Stone has several articles on BT cotton in India
A survey article by Evolution in Action: Plants Resistant to Herbicides by Stephen B. Powles and Qin Yu in Annual Review of Plant Biology is behind a firewall but some of Stephen Powles earlier papers are at his university site .
Link to an interview with Powles Powles: weed resistance will worsen via the excellent article by Carl ZimmerHow To Make A Superweed. Powles says "The three big countries for glyphosate resistance will be the United States, Argentina and Brazil.

That’s because all three countries have massively adopted Roundup Ready crops. The same problems being experienced in the United States are appearing, will continue to appear and will explode in Argentina and Brazil. But leading the pack is the United States."

Australian producers “have had a long-term problem with multiple herbicide resistance in ryegrass. We’ve learned that such an environment requires diversity.

“We’ve learned a few tricks to keep such weeds under control. We won’t be forced out of business by the situation. But to survive, we’ve had to introduce some practices into our farming systems.

“One of them is in our seeding rates — and our main crops are wheat, barley and canola — have risen by up to 40 percent. We’ve tried to make our crops more competitive against the weeds because we can’t be so reliant on herbicides. That simple agronomic practice — as well as manipulating our crop-seeding date — has meant we’ve done a pretty good job of suppressing weeds.

“In the United States, over the time the great Roundup Ready technology has been available, seeding rates for soybeans have actually gone down. That’s because it’s been easy to kill weeds with Roundup. I’m not sure if the same is true for U.S. cotton.

“So, U.S. farmers will increase their seeding rate. They won’t want to do that because of the expense. But if you can’t kill the weeds with glyphosate anymore, that’s one thing that will be tried.

“Another thing that’s coming is herbicide rotation. It may be counterintuitive, but I always say to farmers, ‘If you’re getting great weed control with a herbicide, change it!’ Diversify your herbicides.”

In Australia, “we use any herbicide that still works but don’t use them all the time. We rotate them and mix them in a smart way.

“Finally — and this may be considered a bit far out — is Australian farmers have realized we must do something about the weed seed production. We don’t want them to return to the crop field. We have a few no-chemical — as well as chemical ways — of stopping weeds producing seed.

“I think U.S. farmers will find something similar. Dead weeds don’t produce seed and therefore don’t pass on resistance genes.”

Towards the end of their paper Powles and Yu say "There has been insufficient attention and appreciation of the role of herbicide dose in resistance evolution, and yet where herbicides are used at sublethal dose (some plants are affected but survive), there can be rapid resistance evolution (110, 111). High herbicide dose results in high mortality but selects for rare resistance genes capable of endowing high-level resistance. However, selection at lower herbicide dose (most plants killed but some survivors) selects for all possible resistance-endowing genes, both weak and strong. Especially in cross-pollinated species this can allow the rapid accumulation of resistance genes. Considerable research attention to the role of herbicide dose (selection intensity) on resistance evolution is justified......Finally, we believe that unraveling the precise details of the biochemical, genetic, and molecular means by which plants evolve herbicide resistance will contribute to wiser use of precious herbicide resources, new innovations, and more sustainable strategies for pest weed management. Through this knowledge we believe that there will be future chemical innovations such as P450 synergists to overcome metabolism-based resistance, judicious herbicide combinations, and conceptualization of new resistance-breaking herbicide structures to overcome target-site resistance. Similarly, this fundamental knowledge is essential in creating realistic population genetics/management simulation models and practical control strategies to achieve sustainability through integrated and diverse weed control strategies that maximize herbicide longevity. As there are no foreseeable new technologies that can rival herbicides for weed management in world cropping, herbicide sustainability is an imperative that must be achieved to help guarantee world food supply. Thus, the major challenge to herbicide sustainability posed by the global evolution of herbicide-resistant weeds demands considerable ongoing public and private sector multidisciplinary research focus."

In other words, it is a complicated affair where a strong liason between science and farm is needed. This seems to be the case in countries like Australia. Glenn Stone talked of technology deskilling farmers in his paper Agricultural Deskilling and the Spread of Genetically Modified Cotton in Warangal.
P.S. Links to related posts with excerpts We’ve A Super Weed, Super Weed, We’re Super-Weedy, Yow and

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