Bill Johnson talked about managing current resistant weeds and protecting further weeds from developing recently. He spoke to farmers and dealers at an event hosted by Bayer at their plots in Wayne County.

Related: Glufosinate requires different application techniques than glyphosate

Weed resistance has developed after years of use of various herbicides. There are more than a dozen weeds resistant to glyphosate, and it has garnered attention because they are key weeds, and because it is forcing growers to switch away from the glyphosate-alone or glyphosate as the primary herbicide system that worked for well over a decade.

Missed mark: This velvet leaf belongs to a species Bill Johnson and others many years ago would be among the first resistant to glyphosate. It didn't happen that way.

Actually, there are more weeds resistant to the ALS herbicides, Johnson says. Some 45 weeds are known to be resistant to ALS herbicides.

So far Liberty herbicide for Liberty Link crops has a good track record, Only one weed has shown resistance to glufosinate, the active ingredient in Liberty. It's an Italian ryegrass in California, found in irrigation ditches in a nut grove, likely resulting from years of continuous use.

That doesn't mean other weeds won't develop resistance to glufosinate if it is not handled with good stewardship.

"We know that resistance genes exist to all herbicides, even those not yet invented, out there in the weed population already," Johnson says. 'The key is using management strategies so that resistance does not become an issue down the road."

Someone asked which would be the most likely weeds to develop resistance to glufosinate, or any other chemistry, in the future. "That's a hard one to predict," he says.

Just how hard? Johnson explains that he and other Extension weed specialists from the Corn Belt states talked about future resistance that might develop to glyphosate in a session about 20 years ago, when the technology was new.

Related: Managing Herbicide Resistant Weeds

"Our guesses were that the first resistant weeds to glyphosate would be velvetleaf and morning glory," he notes. "So you can see how good we are at predicting what weeds might become resistant. It's just not possible to do. "

In the coffee shop, it is known as Palmer pigweed. In university circles, it is referred to as Palmer amaranth. Whatever you want to call it, this weed is the No. 1 weed to watch. Stay on top of your control plan with our new free report, Palmer Amaranth: Understanding the Profit Siphon in your Field.