Only three years before Iowa waterhemp disaster

Richard KellerGroup listens to Mike Owen as huge waterhemp is in the background during a Bayer CropScience Respect the Rotation tour. University weed scientists and Bayer CropScience representatives presented evidence of major glyphosate resistance in waterhemp occurring in Iowa during a Respect the Rotation show-and-tell plot tour and information meeting. The purpose of the meeting was to warn growers, ag retailers and professional agronomists to “get out front of weed resistance instead of playing catch up.”

Growers and ag retailer agronomists toured a 10-acre field plot in north central Iowa near Ellsworth. Media toured the plots with representatives of Asmus Farm Supply, which is based out of the northwest Iowa town of Rake.

Two university weed scientists presented their points of view—Mike Owens, Ph.D., Iowa State University professor, and Jason Nosworthy, University of Arkansas associate professor. A former university weed scientist also made brief comments.

Owen noted, “There has never been anything like glyphosate in the history of agriculture” because of its efficacy, simplicity and convenience. He said it was inevitable that resistance would develop to glyphosate. It should have only been a question of how long because the obvious example of weed resistance occurred with ALS inhibitors in Iowa during the late 1980s.

That ALS resistance has not gone away as Owen has not been able to find a waterhemp population in the state that isn’t still ALS resistant. Once waterhemp is glyphosate resistant, it could be eternally resistant to both ALS inhibitors and glyphosate. Waterhemp in various locations of the nation has been found to be resistant to five modes of action—HPPD, ALS, PPO, atrazine and glyphosate. And Owen said this is “really problematic.”

Mode of action rotation with a pre-emergence herbicide and the same with post-emergence herbicides plus mechanical weed control as necessary was the message from Owen. Professional agronomists have to make recommendations that preserve the technology we have today for as long as possible by using full rates in combination. He explained that the last new herbicide mode of action discovery was the HPPDs approximately 22 years ago and no new ones are on the horizon.

“We are lucky to have a lot of older herbicides that still work but are not simple and convenient,” said Owen, about soybean weed control in the Midwest.

He told the ag retailers, “It is hard to sell stuff they (farmers) don’t want to buy, but you have to work at it.” Selling those additional herbicides is the only way glyphosate can be available for use in appropriate and necessary ways in the future.