Rice cutgrass is an emerging Arkansas weed problem — particularly in zero-grade, reduced tillage and water-seeded crops.
“I'm getting many calls on this,” said Bob Scott, Arkansas Extension weed specialist, at the recent Southeast Branch Station field day in Rohwer, Ark. “Problem acres seem to eke up a bit more every year.”
Scott passed a small pot full of the grass around to those on the tour.
“If you've never seen or held it, check this out. When you grab at it, it will pull against your skin.”
Normally, the weed is relegated to ditch-banks. But when tillage is taken out of the picture in continuous rice fields, it emerges as a problem.
Another big reason cutgrass has become a headache: Command, Ricestar, Clincher, Regiment and other herbicides have very little activity on it. Prior to Clearfield rice coming on the scene, “we had some success with 1- to 1.5-gallon rates of glyphosate per acre in the fall. That fall application is an attempt to reduce cutgrass for the following spring.”
Since Clearfield's arrival, farmers with the weed have reported two applications of Newpath at 4 ounces post “are pretty good. Many times, in order to gain control, a Beyond application is also needed. But outside Clearfield, you're left with a major application of glyphosate in the fall.”
Glyphosate drift remains a huge problem for Arkansas rice.
“Drift has certainly gotten the attention of the state Plant Board (which is responsible for investigating drift complaints). This year, approximately 47 percent of the complaints received by them regard glyphosate drift on rice. And it isn't over — the late-season drift cases are still occurring.”
Until 2,4-D damaged thousands of northeast cotton acres, glyphosate drift was dominating phone calls at the Plant Board. Now, there are many calls on each problem.
“I was in a rice field yesterday with about 5 to 10 percent of the heads affected,” said Scott as he passed around blanked rice he'd pulled from a drift field. “This is officially known as ‘sudden glyphosate syndrome.’ The reason it's sudden is the farmer may not realize the herbicide has drifted onto his field until the heads emerge. At that point, suddenly he has a problem.”
The injury occurs only when the drift occurs after panicle initiation and can cause devastating yield drops. Uptake of the herbicide “is translocated into the point where the seed head is being developed. It interferes with seed development and reduces flag leaf. As far as symptomology, that's what separates it from straighthead.”
Confusing the situation, Newpath drift can show similar effects.
“One difference between them is you'll often see the Newpath drift immediately through leaf burn, a stunting of the plant, smaller seed heads, malformed seed heads and other things.”
It's a common misconception that the drift is mostly caused by air applications. Approximately half of the drift complaints Scott works — “and that lines up with what the Plant Board has found” — are from ground applications. The difference is an aerial complaint may involve three fields while a ground complaint is only in one field.
“Most all the drift problems I've seen are associated with spraying in excessive wind after panicle initiation. It only takes about 1 to 2 ounces of Roundup Weather-Max to blank seed heads in a rice field. At a 22-ounce per acre rate, all you need is a tiny fraction to drift.”
Has Scott looked at nozzles that those responsible for the drift have been using?
“No, I haven't. Most of the guys use air-induction, low-drift nozzles. But some don't. There doesn't seem to be a nozzle component to the problem.”
Can the symptomology be caused by other herbicides?
“As far as seed heads, the problem is often mistaken for straighthead. The reduction in the flag leaf is very characteristic of glyphosate damage. Something else to look at is any hemp sesbania or jointvetch in the field. If those are yellowed, it was probably caused by glyphosate. Newpath doesn't hurt those.”
As for new herbicides, there's a “definite need to bring back Collego. We thought it was back this year.”
A small company was formed to bring back a similar product under the name Lockdown. The company had EPA approval, “but had some manufacturing troubles and ended up not producing enough material to meet demand.”
Scott said a few fields were treated in a test run for Lockdown. It performed “a lot” like Collego.
“If everything goes well, it should be available next season. I get a lot of calls on late jointvetch. We need a consistent product for that weed and this could handle it.”
Regardless, don't leave jointvetch late. “Get it with Facet pre or a good pre-flood broadleaf program. Once vetch gets big it's very hard to control.”
Much of Scott's research focus has shifted away from grasses to the broadleaf spectrum.
“That's because Command, Ricestar, Clincher, Regiment and others have come along. The barnyardgrass issues have been resolved for the most part.”
Now, companies seem intent on filling in the gaps on the broadleaf side. Scott and colleagues are currently investigating a few new products from Valent and Dow.
“Those companies both have new compounds that are still a ways from market but they're in the research pipeline.
“We're also in the third year of evaluating (Strata) from Italy. The company says it should be available in 2007.”
When research first began with Strata, it was believed to be a grass compound.
“We checked it on barnyardgrass and essentially wasted a year of research. It isn't a material for that.
“It turns out Strata acts a lot more like Permit. Most of our comparisons this year have been done against Permit. I like it in all the same combinations and tank-mix partners that Permit is good with. But Permit is better on yellow nutsedge.
“The company realizes that, though, and they've said it will be priced competitively. If you don't have yellow nutsedge, it should be an option.
“I told them if they made Strata cheap enough, growers would figure out how to make it work.”