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The best way to no weeds is to know weeds

Agriculture.com Staff 01/26/2010 @ 9:48am

Back in 1996, competitors of Monsanto faced a dilemma regarding Roundup Ready soybean technology.

Farmers liked it. No, they loved it. "First, there was denial, saying it wouldn't happen, there would be yield drag," recalls Michael Heinz, who headed BASF's crop protection division before heading the global Ciba integration team last year.

This concern soon passed. Farmers nixed other soybean herbicides like a runaway bride who left a spurned suitor at the altar.

"A couple years later, we sat together and asked ourselves, ‘Should we exit herbicide research?' " says Heinz. "But if we did that, it would take a long time to get back in the game (if matters changed)."

Matters eventually changed, though slowly. Farmers continued to adopt glyphosate-tolerant systems to the point where they are now used on around 95% soybeans acres and 70% of corn acres.

"Growers thought there would never be any more problem with weeds," says Mike Owen, Iowa State University Extension weed specialist.

Not exactly.

Small cracks initially surfaced in glyphosate's weed control armor. In 2000, University of Delaware weed scientists confirmed a marestail biotype that was resistant to glyphosate. Now, it's estimated glyphosate-resistant marestail infests 5 million U.S. crop acres.

Meanwhile, biotypes of nine weeds in 20 states have been found to be glyphosate-resistant. Several weeds -- such as biotypes of common waterhemp -- resist multiple modes of actions.

All this isn't a knock against glyphosate. Glyphosate's complicated mode of action, no soil residual, and little or no ability by plants to metabolize it make it a low weed-resistance risk. Weeds became resistant much quicker to herbicides with narrower weed spectrums and longer soil residual periods, such as atrazine and ALS inhibitors like Pursuit.

It's just that use over millions of acres for over a decade kicked in the law of the jungle.

"All agronomic practices exert selection pressure," says Owen.

In glyphosate's case, all that was needed was selection of a resistant biotype that may have initially tallied just one in 100 million.

Back in 1996, competitors of Monsanto faced a dilemma regarding Roundup Ready soybean technology.

"Glyphosate is still going to be the number one component of any weed-control program out there," says Owen.

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