Group listens to Mike Owen as huge waterhemp is in the background during a Bayer CropScience Respect the Rotation tour.
Group 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.

Nosworthy provided data explaining research showing the success of 15-inch soybean planting canopying earlier than 30-inch rows and the potential for higher seed populations helping keep weeds from emerging following a pre-emergence herbicide application.

He further noted, “Using a herbicide that is 95 percent effective will be a failure.” Growers cannot allow resistant weeds to spread their seed. “We have got to get weeds out of fields before they go to seed.”

In general, he said Arkansas is a disaster in terms of Palmer amaranth that is glyphosate resistant, and Iowa is two to three years behind Arkansas with waterhemp being the pigweed-family glyphosate-resistant weed that will take over fields.

He said if growers aren’t proactive and take recommended steps to preserve glyphosate efficacy, “In three to four years, you’ll have growers who are going to completely lose a crop.”

In summary, he recommends growers look at planting in narrow rows and higher seed populations, making sure to reduce the weed seed bank by keeping weeds from going to seed and definitely using residual herbicides in a weed control program.

Private Arkansas research consultant and former University of Arkansas weed scientist Ford Baldwin said in Arkansas “we have basically driven the world’s greatest herbicide off the cliff.” He was the most pessimistic speaker about the Arkansas situation by saying, “It is too late to get the glyphosate technology back.”

Baldwin and all the speakers said midwestern farmers have a chance to save the technology, but they have to react immediately for the 2012 planting season with five-year planning for crop rotation and herbicide rotation. Bayer has been licensing a seed trait, Liberty Link, allowing over the top Ignite herbicide use.