Herbicides are "fantastic technology," Stephen Powles told delegates at the Pan American Weed Resistance Conference Tuesday in Miami. "But," he added, "some are too widely used" on too few crops.
Powles, a plant scientist based in Australia, is acknowledged as a leading world expert on herbicide-resistant weeds.
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| Growers hoping to continue to use glyphosate had best come up with more diverse rotations than corn-soybeans or soybeans-soybeans, Stephen Powles warns. |
In North America, he explained, too much farmland rotates between corn and soybeans, and in some regions, cotton. In all three crops, the same or similar weeds need control, and that control tool is usually glyphosate.
In parts of South America the crop rotation scene is even less diverse, with growers going from glyphosate-resistant soybeans to glyphosate-resistant soybeans repeatedly. And in Australia, as another example, he noted a popular rotation is wheat, wheat, wheat.
Powles conceded plants are more readily able to evolve resistance to some herbicides (Group 1 and 2 products, for example) than others such as glyphosate and glufosinate ammonium (Liberty).
But he predicted that if present trends continue, glyphosate will be driven to redundancy in what he called "the U.S. glyphosate belt" (the primary cotton/corn/soybean region).
He also warned that any large-scale move to Liberty as a replacement would expose that herbicide to the same risk, even given that no Liberty-resistant weeds have yet been confirmed.
In Powles' view, glyphosate "is the world's greatest herbicide -- a one-in-100-year discovery up there with penicillin."
We need to do everything possible to protect it, he stressed, but we're not. With some exceptions such as Canada, he added, glyphosate resistance is appearing all over the world. "And already, three different types of resistance mechanism have been identified."
In minimizing the spread of resistance, he concluded, the key word is "diversity" -- diversity in crops and diversity in herbicides.