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Newpath-resistant barnyardgrass (update)

A 60-acre field in central Arkansas’ Prairie County has been confirmed with the Mid-South’s first incidence of barnyardgrass resistant to Newpath, propanil and Facet.

With the vast majority of the state’s rice expected to be planted in Clearfield varieties (which make use of Newpath) weed specialists say this is only the beginning.

Rapid adoption of the popular Clearfield technology by Mid-South producers (for more, see along with the fact that barnyardgrass is highly prone to evolve herbicide resistance means the discovery “wasn’t unexpected,” says Jason Norsworthy, weed scientist and associate professor at the University of Arkansas.

“But in the Mid-South — maybe even the United States — this is the first time I’m aware of a biotype having resistance to three modes of action in a single field.”

For more on resistant barnyardgrass, see and

Ken Smith was hoping it would be a few more years before such Newpath resistance showed up. “When this spreads — and it will — we’ll have only Command, Ricestar-type products and Prowl left for controlling barnyardgrass,” says the Arkansas Extension weed specialist. “Weed control in (the Prairie County) field is now severely limited. Growers need to know resistance can happen quickly and results in serious consequences.”

The field

Last fall, called to a rice field west of Devall’s Bluff, Ark., by a worried consultant, Brent Griffin saw “several large areas of barnyardgrass although it wasn’t thick enough to hurt the rice or take it down. It was randomly scattered around the field.”

Griffin, Prairie County Extension staff chair, says where escapes had occurred “the plants were running one or two per square foot. The grass had blown through two Newpath applications, had come through a propanil/Facet application and some Clincher applications late. I think the Clincher was applied just for ‘get back/revenge’ because the grass was too big to control at that point.”

What was “really eye-opening” was an area of the field where 15 ounces of Newpath (a normal rate is 4 ounces per acre) had been applied to the grass. “Even spraying those spots with that much Newpath didn’t kill it.”

Another interesting trait of the escapes is, unlike normal, well-tillered barnyardgrass, they “only had one or two seed heads.” Griffin says weed scientists attributed that to the late-season Clincher application knocking out some of the tillers.

Sufficiently alarmed, Griffin collected samples and sent them in for study.

The greenhouse

Norsworthy — who oversees a weed resistance screening program in Fayetteville, Ark. — says, “Last year, as usual, samples were sent in for us to screen throughout the winter. The samples sent in by (Griffin) were resistant to Facet and propanil.”

That wasn’t a surprise because in recent years, 48 percent of the barnyardgrass samples Norsworthy has screened have proven resistant to propanil, 28 percent are resistant to Facet and 21 percent are resistant to both.

Then Newpath seemed to fail in controlling the Prairie County sample.

“Anytime something is new or odd, we’ll go back and take a closer look,” says Norsworthy. “In this case, we sprayed the grass with eight rates of Newpath and the same with Grasp. We sprayed up to 32 ounces of Newpath, an 8X rate, on two-leaf grass.”

In early April, Norsworthy checked the plants he’d sprayed 21 days earlier. They were “barely bothered. We’d sprayed 20 plants with the highest rate of Newpath and killed zero. Not only that, but the untreated plants were about 18 to 20 inches tall. The treated plants were about 16 inches tall.”

Grasp was only slightly more effective than Newpath on the barnyardgrass. At 16 ounces of Grasp (an 8X rate), “we killed one out of 20 plants. This wasn’t unexpected since Grasp and Newpath are both in the ALS herbicide family and have the same mode of action. Obviously, we had a problem.”

Smith describes the Prairie County barnyardgrass as being “super-resistant — increasing rates, perfecting spray timing, double-shots or the like won’t work.”

To deal with grass weeds in rice, five major modes of action are available: propanil, Facet, Command, ALS herbicides (Grasp, Regiment, Newpath and Beyond) and some ACCase herbicides (Clincher, Ricestar).

“So, in this Prairie County field three of the five key pieces to control barnyardgrass are completely lost,” says Norsworthy. “For the last couple of years I knew a train wreck was coming. Well, the train crashed in this field and the farmer has lost the flexibility and numerous options to deal with barnyardgrass.”

Growers need to fully understand that once a herbicide mode of action is lost, it is gone for good. And once resistant grass is in a field, “it will always be there. Seed is in the soil and not all will emerge in a given year. What does emerge will pass along the resistant gene regardless of whether or not it’s sprayed with a particular herbicide. Going with a herbicide program without Facet or propanil doesn’t mean that resistance will lessen in three or four years. From this day forward, those products will not be effective on barnyardgrass in that field. They will fail.”

Add Newpath resistance to the mix and the Prairie County producer is in a serious quandary.

“If he plants rice, what will he do to manage barnyardgrass? Well, Command, Prowl, Bolero and the ACCase herbicides (Clincher, Ricestar) are still available — but that’s it,” says Smith.

Growers need to be cognizant of the fact they can sometimes be “trapped” in a Clearfield system, says Norsworthy. “Soybeans is the only way out for some growers. Growers tell me they have zero-grade ground that isn’t conducive to growing soybeans and they want to grow continuous rice. In those situations, once they go Clearfield, they can’t do anything but grow it continuously. You can’t go back to conventional rice the year after growing Clearfield and applying Newpath.

“I’ve heard estimates that the state will plant 70 to 75 percent of our acreage in Clearfield varieties. If that happens, it scares me. There are a lot of fields in this state that have been in continuous Clearfield rice for four, five and six years.”

While the Prairie County field is unique so far, “I’m confident it isn’t the only one in the state with Newpath resistance. With the amount of Clearfield rice we’re planting and the amount of Newpath we’re applying, I’m confident we’ll see more.”

The weed scientists say growers must be “proactive” before Newpath-resistance becomes widespread and the Clearfield technology is no longer effective in managing barnyardgrass.

“Already,” says Norsworthy, “options are few — the last thing we need is even fewer.”

For monetary reasons, Norsworthy understands many growers are reluctant to use multiple modes of action and “not ever let the barnyardgrass come up. But that’s the best thing to do. There are very few growers without barnyardgrass on their farm. The key to managing barnyardgrass effectively is laying residuals down before it emerges.”

Once barnyardgrass comes up, “maybe we can kill 90 or 95 percent of it. That leaves 5 percent surviving. Any survivor in the field, even if susceptible, is producing seed. The more seed in the soil, the more likely you are to select for resistance to a herbicide. And any escapes you see are much more likely to be resistant. The more we keep the soil seed bank at a minimum, the lower the risk of resistance.”

Back to the field

In 2004, to help deal with red rice, the Prairie County producer planted Clearfield rice. In 2005, he planted soybeans that were decimated by the deer herd living on an adjacent wildlife refuge. Unwilling to bear the expense of feeding deer, the producer stuck with Clearfield varieties from 2006 through 2009.

“The farmer’s hand was kind of forced into planting Clearfield rice repeatedly,” says Smith. “The soil is inappropriate for cotton, and it’s best to do a Clearfield rice/soybean rotation. Because of deer, he stuck with rice.”

While there may be “extenuating circumstances” for using Clearfield varieties repeatedly, “that’s beside the point — weeds don’t care about extenuating circumstances. Newpath, Newpath, Newpath is what’s brought things to this point.”

For control, the farmer “still has Command, but traditionally in that part of the state, Command doesn’t last season-long,” says Smith. “You put out Command pre-emerge and then, just before it’s time for flood, it breaks down and you get a bit of grass coming in. Newpath had been an option of taking some of that out — as has Facet and propanil. All three of those are now lost there.

“This is a serious situation developing. We knew we’d get Newpath resistance, but I was hoping it wouldn’t be in weeds already resistant to propanil and Facet. Sure enough, that’s exactly where it showed up.”

In recent years, Smith has pointed to frequent flooding in the state as a way that seed from resistant weeds has spread. He hasn’t stopped beating that drum.

“It’s happening, absolutely. As an example, in the (Prairie County) field I could see barnyardgrass seed on the soil surface where the water had puddled. So, you know that seed was floating and congregating where puddles formed. Did they move with the water? Yes, although I’m unsure how far they traveled.”

Prairie County

The Newpath resistance confirmation “has really got me worried,” says Griffin. The weed specialists “think this is just the first of many barnyardgrass resistance issues that’ll show up. Who knows what’s already out there that we don’t even know is resistant yet?”

For this reason, Smith continues to emphasize that Command pre-emergence in a Clearfield system “not only makes good weed control sense, but can prevent the one plant that would resistant to Newpath from becoming a problem.”

Prairie County “is kind of Ground Zero for this,” says Griffin. “We’re on the Grand Prairie and — next to a few fields in Lonoke County — this is the oldest rice-growing region in Arkansas.”

Griffin says the producer with the problem field is “a good, aggressive farmer who is up-to-date and knowledgeable on all the technologies. It can happen to anyone. Outside this one field, (the grower) is a good steward. He’s in a one-in/one-out on rice rotation. He has some acres that are even one year rice/two years in soybeans because of irrigation issues.

“Can you imagine what he’ll have to do to keep this from spreading all over his farm? It’s a huge headache. Whenever they work this piece of property — whether spring tillage or fall harvest — everything has to be blown out, swept out, and scraped off. All the dirt has to be removed to keep this barnyardgrass out of adjoining fields. I hope other farmers are paying attention and doing what they can to keep from being in the same situation.”


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