Fluoridone widens Palmer pigweed control options for rice growers, but stick to the label

Two-year study offers insight on rice cultivar tolerance to newly registered herbicide

University of Arkansas System Division of Agriculture

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Injury to paddy rice 10 weeks after emergence is seen in test plots sprayed with fluridone before the approved timing of the three-leaf stage at the Rice Research and Extension Center in Stuttgart, Arkansas.

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Credit: U of A System Division of Agriculture photo

FAYETTEVILLE, Ark. — A word of caution to rice growers: the herbicide fluridone has become a valuable tool in fighting Palmer pigweed, but it can cause injury to some rice cultivars, depending on when it is used.

Registered under the trade name Brake by SePRO Corporation, fluridone is a residual herbicide used to suppress grasses and broadleaf weeds before they emerge, also known as a preemergence herbicide. In 2023, fluridone was approved by the U.S. Environmental Protection Agency for use in rice at the three-leaf stage and onward. It had already been approved for use in cotton and peanuts.

Fluridone offers a new tool in the arsenal to fight herbicide resistance in Palmer pigweed, said Jason Norsworthy, Distinguished Professor of weed science in the department of crop, soil and environmental sciences for the Arkansas Agricultural Experiment Station and the Dale Bumpers College of Agricultural, Food and Life Sciences. The experiment station is the research arm of the University of Arkansas System Division of Agriculture.

“This is an herbicide that is very effective in controlling Palmer pigweed in rice,” Norsworthy said. “That’s a major weed for us now in rice, more so in row rice than in flooded rice since the flood itself can help take it out.”

Furrow-irrigated rice, also known as “row rice,” has gained momentum with Arkansas rice farmers over the past decade in efforts to conserve water, retain flexibility for crop rotations with corn and soybean, maintain off-season cover crops, and allow for limited tillage.

Although a row rice field isn’t entirely flooded, the bottom one-third to one-quarter of the field often does retain water, Norsworthy said. Since fluridone is an aquatic herbicide — a herbicide that is highly active in moist environments — it can injure intolerant rice varieties located in the wet zones of row rice fields if not applied according to the label.

The goal of furrow-irrigated rice is to achieve increased profit margins by reducing input costs, according to the Arkansas Furrow-Irrigated Rice Handbook.

Tolerance test

In 2022, Norsworthy and a team of Division of Agriculture researchers began a two-year study on a dozen rice cultivars commonly grown in Arkansas to test the tolerance levels when sprayed before and after rice plants emerge.

In the 2022 and 2023 trials, they used Brake’s label rate and twice the label rate. Both tests were done in flooded rice on silt loam soil, but still offer insights into fluridone’s use in row rice, which calls for more frequent and timed irrigations. Traditional rice cultivation that uses levees and gates to manage water, also known as “flooded rice” or “paddy rice,” allows the entire field to be flooded.

Rice cultivars tested included CLL15, CLL16, Diamond, DG263L, Jupiter, Lynx, Titan, PVL02, RT7321 FP, RT7521 FP, RTv7231 MA and XP753.

The study, titled “Rice cultivar tolerance to preemergence- and postemergence-applied fluridone,” was published in Weed Technology by lead author Maria Souza, a Bumpers College graduate research assistant in the department of crop, soil and environmental sciences. Co-authors included Norsworthy; Pâmela Carvalho-Moore, Bumpers College graduate research assistant; Amar Godar, post-doctoral fellow with the experiment station; Samuel B. Fernandes, assistant professor with the experiment station and Bumpers College; and Tommy Butts, formerly with the Division of Agriculture and now assistant professor and extension weed scientist for the department of botany and plant pathology at Purdue University.

Based on their findings, the authors noted that fluridone tolerance is cultivar-dependent, and applications of fluridone in rice before the three-leaf stage should be avoided as required by the label.

Fluridone applied in rice at the three-leaf stage did not cause a yield penalty to any cultivar in 2022, but there was a yield loss for eight cultivars in 2023 at twice the label rate.

The field trials showed that when applied before the three-leaf phase in rice, fluridone negatively affected shoot density, groundcover, chlorophyll content and days to 50 percent heading in most cultivars tested.

“When you apply Brake as a preemergence herbicide and you flood it, the rice has a tendency to go backwards, as noted in multiple trials,” Norsworthy said.

Visible injury varied between years in all experiments, likely due to different environmental conditions, Norsworthy said. In 2022, injury following preemergence applications of fluridone was below 25 percent across cultivars. In contrast, in 2023, more than 30 percent injury occurred to five cultivars, with a maximum of 58 percent observed for one.

Cut soils is also a factor when using fluridone, Norsworthy added. Their research has shown an increased risk for injury to irrigated rice on soil where the topsoil had been removed for elevation changes, also known as “cut ground.”

Tank mixing recommendation

As Norsworthy noted, fluridone is only registered to control weeds before they spring up and when the rice plant has reached the three-leaf rice. So, what’s a row rice farmer to do if Palmer pigweed has already emerged by the three-leaf stage? Essentially, Norsworthy said, it depends on how tall the pigweeds are.

“What we found in our work is that the most effective option is to put Brake out with 8 ounces of Loyant,” Norsworthy said. “A lot of growers are reluctant to apply Loyant by airplane because of the risk of off-target movement to nearby soybeans. But 8 ounces of Loyant by ground in furrow-irrigated rice is very effective on Palmer pigweed and poses less risk of drifting.”

Norsworthy said he and his team have tested tank-mixing fluridone with propanil, but it was only effective on 1 inch or smaller Palmer pigweed. However, Loyant was able to kill 3- to 4-inch pigweed, and Brake’s residual herbicide action suppressed other pigweed from emerging, he explained.

“Depending on the growth stage of the rice, 2,4-D would also possibly be an option,” Norsworthy said.

The study was supported in part by the Arkansas Rice Research and Promotion Board and SePRO Corporation.

Mention of a product name does not imply endorsement by the University of Arkansas System Division of Agriculture.

To learn more about the Division of Agriculture research, visit the Arkansas Agricultural Experiment Station website. Follow us on X at @ArkAgResearch, subscribe to the Food, Farms and Forests podcast and sign up for our monthly newsletter, the Arkansas Agricultural Research Report. To learn more about the Division of Agriculture, visit uada.edu. Follow us on X at @AgInArk. To learn about extension programs in Arkansas, contact your local Cooperative Extension Service agent or visit uaex.uada.edu.

About the Division of Agriculture

The University of Arkansas System Division of Agriculture’s mission is to strengthen agriculture, communities, and families by connecting trusted research to the adoption of best practices. Through the Agricultural Experiment Station and the Cooperative Extension Service, the Division of Agriculture conducts research and extension work within the nation’s historic land grant education system.

The Division of Agriculture is one of 20 entities within the University of Arkansas System. It has offices in all 75 counties in Arkansas and faculty on three system campuses.

The University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.

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Journal

Weed Technology

DOI

10.1017/wet.2025.13 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Rice cultivar tolerance to preemergence- and postemergence-applied fluridone

 

Wild spinach offers path to breed disease resistance into cultivated varieties

Washington State University

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MOUNT VERNON, Wash.—Several varieties of wild spinach that originated in Central Asia show resistance to a destructive soil-borne pathogen that beleaguers growers of spinach seed in the Pacific Northwest—a finding that can be used to breed hardier crops.

Researchers at Washington State University’s Mount Vernon Northwestern Washington Research & Extension Center demonstrated in a new paper that some strains of wild spinach are resistant to Fusarium wilt, a fungal disease that is a persistent problem for growers of commercial spinach seed, and they identified regions of the plants’ genome associated with that resistance.

The findings are important for seed growers in western Washington and Oregon, where a significant portion of the world’s spinach seed is grown and where the pathogen has long been a problem due to the acidic soils.  

“We were very, very pleased we found some excellent resistance when we did the screening and then we followed up with the DNA sequencing and looking at where that resistance might be lying,” said Lindsey du Toit, a plant pathologist who has worked on fighting disease in seed crops for 25 years at WSU’s Mount Vernon NWREC.

Though the new paper, published this month in nature.com’s Scientific Reports, identified several varieties of wild spinach associated with resistance to Fusarium wilt, more study is needed to understand the genetic nature of the resistance. However, seed companies don’t have to wait to apply the findings—they can begin breeding hybrids with the wild spinach varieties that showed resistance.

“You don’t necessarily have to understand the mechanism of resistance in order to use it,” du Toit said. “This is a tool that’s available immediately to breeding programs.”

Spinach consumption has been growing dramatically around the world. In the U.S., the per-capita consumption of the vitamin-rich vegetable has more than doubled in the past 20 years, with a particularly strong market for baby leaf spinach.

Most of the domestic crop is grown in hot, dry regions such as California, Texas and Florida. But growing spinach seed requires a rare combination of seasonal conditions—long, dry summers that aren’t too hot. As a result, around a fifth of the world’s spinach seed is grown in the Pacific Northwest.

But those crops have little resistance to Fusarium wilt, which afflicts spinach by entering through the roots and blocking their ability to take up water. Seed growers have tried to manage this problem by rotating spinach crops on long timeline—a decade or more between plantings—and taking other measures to treat the soil with calcium carbonate to reduce the acidity.

Even so, the prospect of an expensive “wipeout” of an entire crop has remained a continual threat.

In the current study, du Toit and a former post-doctoral researcher in her lab, Sanjaya Gyawali, screened 68 varieties of wild spinach from the region where the plant originated—Uzbekistan and Tajikistan—and compared them to 16 cultivated varieties. Researchers from the University of Arkansas also participated in the study.

They found strong resistance to the pathogen in several wild varieties. They then identified the chromosomal locations associated with the most powerful resistance. Those locations—known as quantitative trait loci—can be used by breeders to introduce more resistance to Fusarium wilt into commercial lines using marker-assisted selection, a technique that uses DNA markers to select for desirable traits.

The work was funded in part by the Specialty Crop Research Initiative of the U.S. Department of Agriculture’s National Institute of Food and Agriculture. The project was also supported by WSU CAHNRS Hatch Projects, and the Alfred Christianson Endowment in Vegetable Seed Science.

 

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Journal

Scientific Reports

DOI

10.1038/s41598-025-98932 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Genome wide association study of Fusarium wilt resistance in Spinacia turkestanica

Article Publication Date

17-May-2025

 

First-of-its-kind global study shows grasslands can withstand climate extremes with a boost of nutrients

Faced with drought, fertilizer helps grasslands grow strong

Binghamton University

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Cedar Creek Long Term Ecological Research Site was one of 26 sites studied as part of a global study examining the effect of drought and nutrient addition on grasslands.

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Credit: Sydney Hedberg

Fertilizer might be stronger than we thought. A new international study featuring faculty at Binghamton University, State University of New York found that fertilizer can help plants survive short-term periods of extreme drought, findings which could have implications for agriculture and food systems in a world facing climate stressors.

“Resources such as nutrients and water have been fundamentally altered by humans on a global scale, and this can disrupt how plants grow,” said Amber Churchill, an assistant professor of ecosystem science at Binghamton University and co-author on the study. “Extreme changes in these resources are therefore predicted to have an even larger potential impact, with implications for a range of economic sectors. This is especially true for global grasslands, where resource availability for water and nutrients directly supports livestock and pastoralism on all inhabited continents.”

To address this issue, the researchers assessed how grasslands respond to extreme drought and increased nutrient availability through field experiments at 26 sites across 9 countries.

“It took what are often very site-specific methodologies, where we're interested in the impacts of nutrients or the impacts of drought and water availability, and it scaled a single site experiment up to something at a much larger spatial scale,” said Churchill. “The ability to test both variation in nutrients, as well as this global change driver of impacts of drought in combination at such a huge spatial extent – that's the really novel aspect of this experiment.”

The researchers added nitrogen, phosphorus, and potassium – essential nutrients that all plants need – as well as a one-time addition of a series of micronutrients. They found that while drought alone reduced plant growth by 19%, adding fertilizer increased plant growth by 24%. Importantly, the combination of the two resulted in no net change in growth, largely driven by grasses that were able to take advantage of the added nutrients even under drought. 

“The really big takeaway is that adding nutrients can offset the impact of drought, and this is really true in areas that are already pretty dry,” said Churchill.

Churchill worked at two of the 26 sites. At the Yarramundi site at the Hawkesbury Institute for the Environment of Western Sydney University, she managed data, recording the number of plants present in the area. At the Cedar Creek Long Term Ecological Research Site in Minnesota, she was in charge of cleaning all data and organizing it to be shared with the network of researchers. 

“In terms of drought, we get less growth; we add fertilizer, we get more growth. As you're seeing some of those idiosyncrasies, the sort of follow-up lines are where it gets a little bit more interesting,” said Churchill. “Traditionally, we might hypothesize that if plants are already limited by water at, say, an arid site, plants may not be able to respond to adding nitrogen. But we actually found the opposite of that, where plants are able to better respond to the nitrogen addition under these more arid conditions. And so that's a really sort of a striking difference than what we might have expected.”

Churchill will be creating similar treatments at Binghamton University as part of the Pasture and Lawn Enhanced Diversity Global-change Experiment (PLEDGE), at Nuthatch Hollow, a 75-acre, “open-air lab” at Binghamton University.

While adding fertilizer might temporarily offset the effects of drought, said Churchill, it’s not a feasible long-term solution.

“In a forage production system where you need to offset the effects of drought, adding fertilizer will remove that effective drought,” she said. “That's a great benefit, but that costs a lot of money. So there's a tradeoff there. It can be a tool used, but it's not going to be the long-term solution.”

Churchill said that in terms of management, the number of plant species growing might be a more important factor in surviving drought.

“We have a prediction that as you have more species, one of those species is more likely to withstand the drought, so you'll get at least some biomass, even if each species doesn’t make it. And so the idea is you'll have more stable biomass over the long term if you have more species present. That's something we can't test with this data set, because we're only looking at one year. But longer-term data sets can look at that sort of a question.”

The paper, “Aridity modulates grassland biomass responses to combined drought and nutrient addition,” will be published May 19 in Nature Ecology & Evolution.

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Journal

Nature Ecology & Evolution

Subject of Research

Not applicable

Article Title

Aridity modulates grassland biomass responses to combined drought and nutrient addition

Article Publication Date

19-May-2025

 

Native turtles return to Yosemite after removal of invasive bullfrogs

Without American bullfrogs, native pond turtles increase at national park

University of California - Davis

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Sidney Woodruff of UC Davis holds a northwestern pond turtle at their field site in Yosemite.

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Credit: Courtesy Sidney Woodruff

The call of American bullfrogs was deafening when scientists from the University of California, Davis, first began researching the impact of invasive bullfrogs on native northwestern pond turtles at Yosemite National Park.

“At night, you could look out over the pond and see a constellation of eyes blinking back at you,” said UC Davis Ph.D. candidate Sidney Woodruff, lead author of a study chronicling the effects of removal. “Their honking noise is iconic, and it drowns out native species’ calls.”

But the ponds of Yosemite sound different today, with a chorus of native species making themselves heard. The researchers’ study, published in the May issue of the journal Biological Conservation, found that as the park was depopulated of bullfrogs, northwestern pond turtles began to return. The study suggests that removing invasive bullfrogs may be necessary in priority conservation areas to help pond turtle populations recover.

A western icon

The northwestern pond turtle is one of two species of western pond turtle, the other being the southwestern pond turtle. Together, they are the only native freshwater turtles in California. Yet the western pond turtle has disappeared from over half of its range, which stretches from Baja, California to Washington state.

One of the biggest threats to the species is the introduction of American bullfrogs, which are native to the eastern United States but were introduced in the West, where they prey upon small, young turtles.

“One reason American bullfrogs are among the top worst globally introduced pests is because they eat everything – anything that fits into their mouth,” said senior author Brian Todd, a UC Davis professor in the Department of Wildlife, Fish and Conservation Biology. “They’ve been causing declines to native species everywhere they’re introduced, which is around the world.”

Turtles return after bullfrogs croak

American bullfrogs were introduced throughout Yosemite in the 1950s and were well-established in multiple regions in the park by the mid-1970s. Field observations of bullfrogs eating native turtles suggested their arrival could be a factor in the northwestern pond turtle’s drastic decline, but little research was available to confirm that theory. To research a potential link, the authors conducted a seven-year study to examine the impact of removing bullfrogs on native turtle populations. Between 2016 and 2022, they monitored four sites at Yosemite where native turtles persisted — two with bullfrogs and two without.

Where bullfrogs were present, only older, large turtles — too big to fit in bullfrogs’ mouths — remained. Researchers even found juvenile turtles — along with newts, snakes, small birds and rodents — in the stomachs of captured bullfrogs. Turtles were up to 36% larger and up to 97% heavier at sites where bullfrogs were present, suggesting younger turtles are not surviving at sites shared with bullfrogs.

Turtles were 2 to 100 times more abundant where bullfrogs were absent. Not until bullfrogs were nearly eradicated from the sites in 2019 did scientists observe the first juvenile turtles at the formerly “bullfrog-present” ponds.

The value of native turtles

Western pond turtles, including northwestern pond turtles, play important ecological roles, cycling nutrients and energy through aquatic systems as they peacefully go about their lives. Proposed as a threatened species under the Endangered Species Act, their intrinsic value goes beyond the legal and ecological, Todd said.

“All across the state we have one native freshwater turtle, and it’s the western pond turtle,” Todd said. “If it disappears, we have no other freshwater turtles that are supposed to be here. It’s part of our natural heritage.”

The authors emphasize that eradicating non-native bullfrogs is not a likely solution for every location but could make sense for priority conservation areas where the risk of reinvasion is low and where native turtle recovery is most promising.

“As bullfrog presence declined, we started to hear other native frogs call and see native salamanders walking around,” Woodruff said of their field work. “It’s nice to be able to go back to these sites and hear a chorus of native frogs calling again that previously would not have been heard.”

Additional coauthors include Robert Grasso of Yosemite National Park and Brian Halstead of U.S. Geological Survey.

The study was funded by the Western Pond Turtle Range-wide Conservation Coalition, Yosemite Conservancy, U.S. Geological Survey and USDA National Institute of Food and Agriculture. 

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Journal

Biological Conservation

DOI

10.1016/j.biocon.2025.111090 

Method of Research

Experimental study

Article Title

Effects of invasive American bullfrogs and their removal on Northwestern pond turtles Author links open overlay panel

Article Publication Date

19-Mar-2025

An American bullfrog tadpole, left, is bigger than the young native northwestern pond turtle in this photo. Bullfrogs often prey on native turtles in the western U.S., contributing to their decline.

Credit

Sidney Woodruff/UC Davis

This juvenile northwestern pond turtle hatchling was collected from an American bullfrog's stomach near Yosemite National Park.

Credit

Sara Gabel

The American bullfrog is native to the eastern United States but was introduced in the West. Voracious eaters with large mouths, their diets can include birds, bats, rodents, newts, snakes, and turtles. (National Park Service)

Credit

National Park Service

A northwestern pond turtle hatchling at a study site in Yosemite.

The field crew, including UC Davis scientists, hikes in the study area near Yosemite National Park.

Credit

Sidney Woodruff/UC Davis