With herbicide-resistant weeds on the increase and no new chemistries on the horizon, soybean farmers — and especially no-tillers — must carefully review their weed-control options, according to a panel of four field agronomists at the recent 2003 National No-Till Conference in Indianapolis, Ind.

They advised:

• Use tankmixes or premixes of herbicides with different modes of action.
• Avoid no-tilling crops that are resistant to the same herbicide back to back.
• Stick with the resistance management strategy that makes the most economic sense for your operation.

“Herbicide-resistant biotypes are increasing every year,” says David Lamore, senior technical service representative for Bayer CropScience at Bryan, Ohio. “You have to choose a path of least resistance.” Lamore notes that although occurrence of triazine-resistant weeds is leveling off as the use of triazine herbicides has, the appearance of resistance to other chemistries offsets this trend.

Glyphosate Resistance.

The big news is confirmation of glyphosate-resistant marestail, says Dave Ruen, Dow AgroSciences customer agronomist at Lanesboro, Minn. He says research presented at the recent meeting of the North Central Weed Science Society in St. Louis, Mo., documents the existence of resistant marestail in the Delmarva Peninsula, New Jersey, Kentucky, west Tennessee, southern Indiana and Ohio. Without sound resistance management, the new weed type could quickly spread to other areas.

“Glyphosate has been used on tens of millions of acres, both as a burndown and in-crop,” Ruen says. “Now we’re seeing a pattern of resistance developing similar to the ALS inhibitors.” Lambsquarters, another problem weed in Roundup…