Roundup resistance is not a matter of ‘if’ but ‘when’ so much for this being a sustainable approach. “...even with control rates of greater than 90 percent with single applications of Roundup Ultra, “plants that survived Roundup Ultra initiated new growth, and survivors were noted even at rates as high as 2 gallons per acre.” Although “visibly stunted,” he said, “these plants also set what appears to be viable seed.” [from press release from the Univ. of Missouri]
As predicted by many weed ecologists and observed in most regions where RR [GM - Roundup Ready] beans have been planted for more than three years, herbicide reliance continues to increase as a result of the combination of weed shifts and resistance.
Depending on weed species present and use of an pre-emerge or at plant herbicide, herbicide pounds applied and/or acre-treatments per acre are clearly rising compared to the early days of RR beans when one post-emerge application, if time[d] just right, was effective in most reasons.
Many people predicted, accurately, that this seeming “silver bullet” would not last. With Roundup off patent and generic products coming on the market, the price per acre treated with Roundup, or Roundup-clones has been falling at about the same or a somewhat faster rate than the increase in necessary application rates.
For the time being, farmers will “benefit” according to analysts who keep score only in terms of short-run herbicide expenditures per acre. But soon””certainly not more than three more years””glyphosate efficacy will slip off the edge of the table and rates per acre 2-X to 3-X today’s (but which will cost little more because of continued price cuts) will work on only a subset of weeds, making the system no longer economically viable, even if the RR bean tech fee is dropped (this largely because of yield drag even in the presence of good weed control). And then soybean producers will move on, but to what? At what cost?
The below press release is from the Univ. of Missouri and is based on a recent conference:
Forrest Rose, Information Specialist - 7 December 2000
Despite signs of resistance in waterhemp, glyphosate still provides effective control
COLUMBIA, Mo.””Despite evidence that a population of waterhemp has been found insensitive to normal use rates of glyphoshate-based herbicides, glyphosate remains among the most effective and economical herbicides available, University of Missouri weed scientists said at the MU Crop Management Conference.
“Since the inception of glyphosate-resistant crops in 1996, researchers have said that the onset of weed resistance to glyphosate was not a matter of ‘if’ but ‘when,’” said Reid Smeda, MU assistant professor of agronomy. His research showed that while glyphosate-based herbicides such as Roundup provide “excellent control of over 90 percent of the targeted plants, there were some survivors.”
At a field site in Northern Missouri, Smeda and other MU weed scientists applied different rates of Roundup Ultra to plots of waterhemp at various plant growth stages in a non-crop situation. They found the best control method to be a broadcast application at one pint per acre when the weeds were 2 to 3 inches high, followed by a one quart-per-acre application at 4-to-8-inch or 12-to-16-inch weed regrowth.
Other effective treatments included a one-quart application on 4-to-8-inch or 12-to-16-inch plants, followed by a one-quart application on a 4-inch regrowth.
“Once we got to that one-quart rate on plants surviving the one-pint rate, we pretty much wiped them out,” Smeda noted. But even with control rates of greater than 90 percent with single applications of Roundup Ultra, “plants that survived Roundup Ultra initiated new growth, and survivors were noted even at rates as high as 2 gallons per acre.” Although “visibly stunted,” he said, “these plants also set what appears to be viable seed.”
Glyphosate-based products aren’t the answer to every problem, said Andy Kendig, Extension weed specialist at MU Delta Research Center in Portageville, Mo. “But they’re simple, cheap and effective.” Regarding the range of Roundup-imitator herbicides, he added: “It takes a lot of imagination to say that one is better than the other.”
His research at Delta Center showed that two post-emergent applications in Roundup Ready soybeans resulted in yield increases of about five bushels per acre over plots that had been treated only once with Roundup tank mixtures. A pre-emergence application that closely matched the weed spectrum followed by one Roundup application yielded more than two Roundup applications. A poorly matched pre-emergent treatment followed by one Roundup application yielded about five bushels per acre less.
“Individual producers are still the best judge of how to use Roundup on their farms, but we’re showing a slight edge to a pre-emergence herbicide in a Roundup program,” Kendig said.
The conference was sponsored by the MU College of Agriculture, Food and Natural Resources, University Outreach and Extension, the MU Commercial Agriculture Program in cooperation with MO-AG Industries Council.
Charles Benbrook Ag BioTech
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