Annual grasses — barnyardgrass, broadleaf signalgrass and sprangletop — are troublesome weeds for rice producers. Almost every rice farm in Arkansas has one or more of these species to worry with every year.
“So far, our base control has been to spray Command or Facet early,” said Ken Smith, Arkansas Extension weed scientist. “For various reasons — weather, soil types, water management — the pre-emerge treatment of Command or Facet doesn’t always hold the grasses down until flood. Often, there’s re-germination and another flush of these annuals. We need something economical to control them.
“Two products that we’ve had for post-emergence that control fairly good size grasses are RiceStar and Clincher. Now, the old RiceStar had extra safener — too much safener, actually. Bayer took their old Whip herbicide (a product unsafe for rice) and put a safener in it so rice producers could use it. Well, they put in too much safener and it wasn’t killing much grass.”
Last year, Bayer addressed this problem by removing some of the safener and reformulating the product. The result: RiceStar HT — one of the reasons Bayer invited crop consultants to a meeting in Mountain View, Ark., on March 10. Both Smith and Ford Baldwin, weed scientist and Delta Farm Press contributor, spoke on the herbicide.
Currently, the maximum rate of RiceStar HT is 17 ounces per acre. In many fields, that amount wasn’t “quite adequate,” said Smith. “If everything was just right — moisture, grass size was small — then 17 ounces did okay. But things aren’t always perfect. Bigger barnyardgrass along with drier soils showed that 17 ounces wasn’t enough. That rate missed grasses.”
To put that in perspective, “Clincher’s maximum rate was fine if conditions were just right. If conditions weren’t optimal, Clincher worked no better than RiceStar.”
With research showing higher rates working better, Bayer asked for and received a 24c exemption from the Arkansas Plant Board allowing a 24-ounce rate of RiceStar HT.
“Our studies all show those increased rates are still safe for rice but are much more effective on larger grasses,” said Smith. “Up to a 24-ounce rate gives us another tool to control grasses in less than ideal conditions.”
Along with several others in the room, Baldwin was involved in the early research on RiceStar. “It had a bit of a stigma to overcome,” he said. “Several of us remember when Whip was introduced as a herbicide. It looked very good in the research program, but when it got into the field, it faced some things we couldn’t control environmentally. That led to way too much crop injury and bad experiences for some of us.”
When RiceStar — Whip with a safener — was later introduced into the University of Arkansas research program, “the first thing I wanted to do was find out if it was a snake oil or if the safener really worked,” said Baldwin. “Some of the first studies we designed were looking at that… After those studies, I was satisfied the safener was the real deal… I thought, ‘This is a good herbicide.’ We could kill some big grass in research trials. But when we finally received the Section 18, it was too late (in the season)… and we were in the midst of a drought with big grass. When we put a lot of it out, it didn’t work as well as expected.”
Baldwin has been interested in RiceStar’s evolution. “For one thing, we’re not getting any new herbicides. Trying to make all those we have available work as best they can is of real interest to me. The HT route was the right way to go. It answered the safener question, and we’ve all done enough research work to (alleviate any concerns) about the reduction of the safener level causing injury to rice. In fact, last year, we were looking at HT and adding some Whip back to it just to see if there was enough safener.”
Last year, Baldwin didn't see a great difference between the 17-ounce and 24-ounce rates. “That’s only because the 17-ounce rate worked so well. I always put it out in good moisture. We were killing big grasses pre-flood. I believe the higher rates will add some consistency to it.
“One thing I noticed when HT came out is I started getting questions from the field. Before, I wasn’t getting any questions about spraying RiceStar. In fact, in some cases if it had a good fit, I’d suggest the product and folks wouldn’t take the bait. Last year, though, we got a lot of calls on HT and got many favorable comments regarding it.”
Another thing to consider is early competition. If you start looking at barnyardgrass in rice, “you begin to lose potential yield about 14 days after emergence,” said Baldwin. “When it comes time to put the water on, I don’t want anything in the field except dirt and rice.”
Bayer has announced RiceStar HT’s price will be cut around 25 percent to $1 an ounce. A company spokesman said there should be enough product to spray 8 percent to 10 percent of the acres treated with postemergence grass products.
The price drop, said Smith, means the product will be “an economical treatment for grasses that have escaped a pre-emergence program. For the farmers’ sake, I’m really glad to see the price drop. We pursued a 24c label and supported the increased rate because we understood it had potential to be economically advantageous to the farmer.”
Smith’s advice to rice producers: make every effort to do everything correctly up front.
“That way, hopefully, they won’t even need an annual grass over-the-top herbicide. If a farmer uses Command properly, if he uses his Prowl/Facet delayed pre- correctly, there will be less need for herbicides like RiceStar HT. In using Command, many times, a good flush to activate it early can hold all the way to flood.”