Weed scientist Connor Webster and his research team conducted 75 rice weed management studies across LSU AgCenter research stations and on farms across the state in 2025.

Webster and his team collected five perennial grass species, including Brooks paspalum, water paspalum, southern watergrass, Habetz grass and rice cutgrass, that cause problems for Louisiana rice producers and hand transplanted them into plots at the South Farm of the LSU AgCenter H. Rouse Caffey Rice Research Station in Crowley.

“All five of these grasses are pretty unique to Louisiana rice production, so there’s not a lot of literature or recommendations out there on how to manage these grasses,” Webster said.

Of these grasses, Brooks paspalum and southern watergrass are the most problematic for growers, Webster said.

“We don’t have a lot of options for the control of Brooks paspalum, and that one perennial grass has really taken off in the past couple of years. It’s showing up everywhere.”

Webster’s team applied various herbicide treatments and identified several herbicide mixtures and standalone herbicides that can provide control of most species evaluated. The preliminary data will be available in the 2026 edition of the Louisiana Suggested Chemical Weed Control Guide and the Rice Varieties and Management Tips.

Barnyardgrass competition

A new study by Webster’s team is evaluating how different varieties and hybrids at varying seeding rates compete with barnyardgrass, which is one of the most economically damaging weeds in south Louisiana rice. They have not finished analyzing the data from the project, but Webster said that the test plots showed marked differences during the trials.

“There was a lot of competition work done by the U.S. Department of Agriculture weed scientists in Arkansas in the ’60s and ’70s,” Webster said. “A lot of that work hasn’t been done again, or it’s been done in a limited manner because it’s such a labor-intensive project.”

Webster’s team is following up with another study that has not been revisited in a few decades. The researchers initiated a similar study on red rice by taking 50 samples of red rice, with most samples taken from southwestern Louisiana, and examining dormancy in those samples.

“We think maybe we’ve seen a shift in the dormancy characteristics, and they’re becoming less dormant because we’ve been able to clean up some fields in three or so rotations with Provisia or Max Ace,” Webster said.

The team plans to increase the red rice seed they collected and expand the study over the next few years.

Novel herbicide study

Since 2021, Webster has trialed tetflupryolimet, a preemergence residual herbicide that features a new mode of action — the first in more than three decades. The herbicide is expected to be registered and approved for use by the U.S. Environmental Protection Agency in November 2026.

Marketed as Keenali, it will be sold as Keenali Complete and packaged with another herbicide, Command. The two herbicides can be mixed to provide better control of a wide variety of weeds, Webster said, but they cannot be formulated together.

Webster assisted with labeling Keenali for water-seeded rice and for FMC, the producer of the new herbicide. He experimented with different rates and timings for five rice varieties and found that the herbicide could be applied at the one true leaf stage, which is earlier than many herbicides, Webster said.

In rice, Keenali has demonstrated good control of barnyardgrass and Amazon sprangletop, a weed that Webster and other weed scientists suspect may be becoming resistant to some herbicides.

“I think this herbicide is really going to help there,” Webster said. “Once sprangletop emerges and gets past three to four leaves, there are very limited options, and the options that we do have are pretty expensive. Having something else that we can use to suppress it will help us a lot.”

Webster has also found that Keenali works well when impregnated onto or surface-coated on fertilizer so rice producers can pay for one aerial application of both inputs.

Newpath and Preface carryover

Webster’s research team also has been performing studies on the yield effects of the carryover of imazethapyr on common rice varieties in fields that are part of a crawfish rotation. To perform the research, the team applied low rates of the herbicide Preface to bare soil and flushed it to incorporate the herbicide into the soil.

“Anytime there is some level of carryover from Newpath or Preface into a conventional or Provisia or Max-Ace line, you’re going to see some sort of maturity delay,” Webster said. “Most of the time you’re going to see a yield effect, but it’s very hard to be able to predict what the yield loss is going to be.”

Webster recommends that producers use Beyond/Postscript herbicide instead of Newpath/Preface as a preflood application when planning to rotate to conventional varieties or Provisia or Max-Ace rice.

Webster presents his research and makes recommendations for producers at the annual AgCenter Rice Research Station South Farm field day, which is held in early June in the weeks before the larger Rice Research Station field day. More information about the 2026 field day will be announced in coming months.