NEWS FROM HORIZON AG
“There's nothing that I see, at least in the short-term, that's going to be here to replace the control we rely on with the ACCase-inhibiting herbicide technology,” said Arkansas weed scientist Dr. Jason Norsworthy, who joined Louisiana weed scientist Dr. Connor Webster and Horizon Ag general manager Dr. Tim Walker on the panel. “Anything and everything that we can do to preserve this technology is valuable.”
Fortunately, research and field experiences, particularly over the past two seasons, have given experts critical insight into managing the Provisia Rice System, from the value of residual herbicides to optimum application timing and rates, to the need for crop rotation and strategic field planning.
“One of the reasons we had the situation in Louisiana in 2022 was some growers opted out of using residuals,” said Dr. Webster. “We didn’t get good coverage with our post-application and that set us up for the problem. Ahead of last season, we strongly emphasized the value of using residuals for both grass and broadleaf weeds to reduce early-season weed competition, and we had only six confirmed outcross populations in 2023.”
He added that since Provisia herbicide can be antagonized when mixed, it is important to use tank mixes that won’t cause a reduction in the efficacy of Provisia herbicide.
Dr. Norsworthy agreed proper use of proven residual herbicides is necessary to keep Provisia herbicide an effective weedy rice tool. “I want Arkansas growers to start with Command® herbicide or a Command-like product to take care of barnyardgrass and all these other grasses because if we are trying to kill weedy rice, we need to make sure we are getting Provisia herbicide to that target,” said Norsworthy. “Unlike with the Clearfield system, during the window of time when rice is going to flood, there is no residual activity to kill weedy rice coming up in the Provisia system.”
When the Provisia technology was launched, both Louisiana and Arkansas recommended the labeled rate at that time of two 15.5-ounce applications, the first at the two-leaf stage and the second as the rice was going into flood.
“That was a mistake,” said Dr. Norsworthy. “For Arkansas, I want to see 11 ounces at the two-leaf stage, 10 ounces as we go to flood, and then another 10-ounce application post-flood. With the two-application approach, you run the risk of weedy rice coming up in that window after flood and you have absolutely no bullets left to control it. Then, if you are in a field that is zero grade, I want to see Rogue® (herbicide) used in that field. That’s the best approach we have in Arkansas to go into harvest without any escapes.”
Dr. Webster also recommends the three-application approach. He noted that growers who went with the three lower rate applications avoided the crop response issues experienced last season by some farmers who made two 15.5-ounce applications when the rice was being impacted by cool, cloudy weather.
Rotation is another key to managing resistance and keeping both Provisia and Clearfield available as effective tools.
“At the end of the day, if we are going to preserve these technologies, we’ve got to put soybeans in that field,” said Dr. Norsworthy. “Some growers tell me they can’t grow soybeans on zero-grade ground but, in the end, we’re not going even to grow rice on that zero-grade ground unless we do something different.”
Dr. Walker added that growers should consider adding Provisia rice to at least a portion of their acreage while weedy rice problems are still minimal and manageable, to maximize the effectiveness of the herbicide and prolong the technology.
“It’s a long-term mindset,” he said. “When the Provisia technology was introduced, it was with a variety that wasn’t nearly as high-yielding as our Clearfield varieties, and it only went out in the worst weedy rice-infested fields. Today’s Provisia varieties are much better. PVL03 was the top planted variety in Louisiana last year and will probably be again this year. It’s better to go out with this technology when you have a 10 percent infestation, get good chemistry results, and then follow a recommended rotation. When you get to a 70 or 80 percent-plus infestation, there are few options. You are backed into a corner and economics may drive you to ruin the technology on your farm.”