A preemergence, grass residual herbicide is proving to be effective in controlling two of the most problematic grasses to rice with little to no crop injury, according to LSU AgCenter weed scientist Connor Webster.

Containing the active ingredient tetflupyrolimet, the herbicide was tested across multiple water management systems including a delayed flood, water-seeded pinpoint flood and row rice.

“It has a narrow spectrum, so it’s not going to control all of our grasses,” Webster said. “But it is going to control probably two of the most troublesome, which are barnyardgrass and Amazon sprangletop.”

According to Webster, studies evaluated varietal response, optimal rate ranges across soil types, how tetflupyrolimet fits into complete herbicide programs, early season water-seeded application timings, optimal preemergence and delayed preemergence herbicide mixtures and applying tetflupyrolimet impregnated on basic fertilizer at planting.

“This is the second year of the variety trial, but we’ve been looking at this product since 2021,” Webster said.

Tetflupyrolimet was also evaluated on cut ground in 2024 and no crop response was observed. Two on-farm trials were conducted in 2024 to evaluate its activity on Neally’s sprangletop.

“It was the perfect situation to be able to evaluate this new herbicide and see how it interacts with hard cut ground, and we really didn’t see any issues with that,” he said.

According to Webster, another big part of the program being examined is a new herbicide that isn’t a new mode of action but belongs to a mode of action that’s been around for the last 30 to 40 years.

“We’re evaluating another new active ingredient that down the road we’ll be able to discuss in more detail, so stay tuned,” he said.

Connor Webster speaks about the new FMC product, tetflupyrolimet, at the South Farm/ Acadia Parish field day with roughly 105 people in attendance. Photo by Gavin Sparks

Other research topics from this year include:

Simulated Newpath/Preface carryover in PVL03, Avant and Jupiter.

Studies were conducted to evaluate the yield effects of carryover of imazethapyr to commonly planted rice cultivars in Louisiana.

Prior to planting, low rates of Preface were applied to bare soil and flushed to incorporate the herbicide into the soil profile. In 2023, the rates ranged from 0 to 1 fluid ounce per acre of Preface in 1/8 of an ounce increments.

These rates did not result in yield differences compared with the nontreated plots, so the rate structure was adjusted in 2024 to 0 to 2 fluid ounces per acre of Preface in 1/4 of an ounce increments. The goal is to determine yield potential of different varieties based on the amount of imazethapyr present in the soil.

Simulated overcast weather conditions and how overcast weather influences Provisia injury.

Since the release of PVL01, crop response has been an issue. In 2023, due to adverse growing conditions, numerous reports of negative crop response were reported. Two studies were designed with different levels of shade cloth covering the plots to simulate different degrees of solar radiation.

One study introduced shade to the plots seven days prior to the Provisia herbicide application; the other introduced shade seven days after application.

In the 2023 season, it was observed that crop response chances increased when overcast growing conditions were present after an application. Crop response was observed for both timings of overcast growing conditions but were more prevalent after a Provisia application. These studies were repeated in 2024.

Identification and control of fimbristylis.

Beginning in 2022, on-farm trials have been conducted in green rice fields on Hebert Farms in Abbeville. The results from these on-farm research trials have made a substantial impact on rice production in south Louisiana.

The information gained from these studies has been disseminated at winter production meetings and provided the vital information needed for recommendations that were made throughout the 2023 and 2024 growing seasons.

Of the herbicides evaluated, 2,4-D provided the highest levels of control followed by Grandstand, Rogue, Novixid and Regiment.

Of the residual control studies conducted, Prowl and Bolero provided the highest levels of residual control of fimbristylis.

Research Associate Ben Stoker and graduate student Gavin Sparks harvest a trial evaluating a new herbicide active ingredient. Photo by Wesley Carr