Unfortunately, barnyardgrass is becoming more problematic for producers in Arkansas. It’s also causing trouble in Mississippi and Louisiana, says Bob Scott, Arkansas Extension weed specialist.

Surveys on “most troublesome weeds” show that barnyardgrass commonly shows up in cotton, soybeans and rice fields, said Scott at the Roy J. Smith Barnyardgrass Workshop held in Stuttgart, Ark. “Sometimes I hear people say they’re in awe of pigweed because it’s so good at what it does. Well, barnyardgrass falls into that same category – it’s extremely good at what it does. If it wasn’t, we’d have cured the sickness a long time ago.”

When propanil came along, it was a game-changer, said Scott. “There are some new technologies coming in the near future that I believe will also be game-changers.

“For now, let’s go over current treatments. The old program: Stam every Monday until the field is clean, right? Propanil followed by propanil followed by propanil. When I arrived in Arkansas in the late 1990s, there was still quite a bit of that mentality. Of course, we still use proponil on a tremendous amount of our rice acreage. However, we just don’t use it as the primary, and only, treatment like in the past.”

Propanil resistance in barnyardgrass was confirmed in Poinsett County in 1990. By 1993 it had spread and 16 of the 38 rice counties in the state had resistance.

“That’s really when (the University of Arkansas’) screening program and educational efforts on resistance began. The screening program is now at the point where, if you’re a consultant – especially if you’re having trouble with weeds in some fields – you should be using it. It’s free and you can just fill out a form and turn in a barnyardgrass sample. Then, you’ll get a report that’ll help you make sound decisions going into the next growing season. That’s a tremendous advantage.”

Herbicides

In 1992, Facet came onto the weed management scene under a Section 18. “What did we do? Not much changed since it was easy to tank-mix it with propanil and roll on every Monday.”

Facet was widely used throughout the 1990s and the first barnyardgrass resistance to it was confirmed in 1999. “And since we used Facet to clean up propanil resistance, it was no surprise to find that the barnyardgrass was resistant to both. That taught us a couple of things. First, what we did wasn’t the best strategy to manage resistance. Second, once a weed becomes resistant to a chemistry, it’ll probably stay that way.”

Eventually, the state received another Section 18 for Command. “I remember consultants saying, ‘Man, that turned my rice white.’ Then, they found out how well it worked and said, ‘You know, on second thought, that color is really a pale green,’” related Scott to much laughter.

Regardless, Command was widely adopted and continues to be “a really good, foundational control for weeds in rice. That’s even though in 2007 and 2008 resistance sites were located with resistance to Command. These are fairly isolated locations and our data pretty much indicates it isn’t a growing problem.”

In 2002, Scott began his job with Extension and it was the first year Clearfield rice came to the market. It took a few years, but Clearfield varieties were widely adopted, ‘catching stride around 2006 all the way to today. Around 2011, almost 70 percent of our rice was in Clearfield varieties.”

One concern from the beginning with Clearfield was mode of action diversity. Sure enough, “ALS (Newpath)-resistant barnyardgrass was found by (University of Arkansas weed scientist Jason) Norsworthy in 2008. About six to seven years is about the general life of an ALS herbicide before resistance is found. The fact that we’re at 2015 and (Clearfield) was introduced in 2002 and we don’t have more resistance is pretty impressive. I’m surprised we don’t have a bigger problem with resistance. Unfortunately, we feel that problem is getting a bit worse.”

Resistance

Currently, no glyphosate-resistant barnyardgrass has been found in Arkansas. “We want to keep glyphosate available for barnyardgrass so we want to keep doing proper resistance management practices.

“Since 2006, we’ve had 284 BYG samples come in and half of them were Propanil-resistant.

“Looking at quinclorac (Facet) resistance, we used the product to clean up barnyardgrass that Propanil didn’t take out. So, guess where the greatest Facet resistance is? The same areas as the Propanil resistance.  

“For the screening program, Newpath and Grasp resistance is what’s looked for. Some of the ALS chemistries are a bit different in nature, although most of the time if barnyardgrass is resistant to one it’ll be resistant to others.”

In 2013 and 2014 , Scott and colleagues saw a tremendous upswing in the percentage of barnyardgrass samples that proved resistant compared to the few years prior. “That’s a major reason this forum needed to be held. The problem is getting worse. In 2013 and 2014, in fact, 29 percent of all samples sent in were Newpath-resistant and 38 percent were resistant for Grasp.

“For some time now Clincher – an ACC-ase herbicide -- has been our clean-up hitter. That isn’t a good position to be in if you’re Clincher. Lots of times, when we get samples, they’ll say, ‘Clincher didn’t work. So, it must be resistant to Clincher.’ Well, during tests, Clincher kills the weed.

“The problem, of course, is the application of Clincher didn’t come first. The first application of Propanil or Facet didn’t touch the weed and by the time Clincher is brought in post-flood, the weed is tall with a seedhead. And in 2014, we had five cases of confirmed Clincher-resistant barnyardgrass.”

Want to hear something scary? “We now have three counties with barnyardgrass resistance to four modes of action. We have seven classes of chemistry to control barnyardgrass in rice. In those three counties, there are barnyardgrass populations where four of them aren’t effective. That’s significant and we must protect the chemistries, the tools, we have.”