Posts Tagged ‘invasive weeds’

Pigweed continues to outflank herbicides

TAGS: COTTONHERBICIDEWEEDSDICAMBARESISTANT PIGWEEDCulpepper-PPO-Greenhouse-Pigweed-W.jpgUniversity of Georgia ExtensionPre-emergence, residual herbicides — including PPO products — remain the best frontline defense if activated timely for a sound weed program, but a greenhouse study in Georgia throws caution flags.Scientific evidence collected this year and last confirms Georgia now has a concerning population of pigweed resistant to PPO-inhibitor Group 14 herbicides.

Brad Haire | Nov 11, 2020https://4648f008829c7812f536ae527c9eb0dd.safeframe.googlesyndication.com/safeframe/1-0-37/html/container.html

The plants in the greenhouse looked a little beat up but remained rigidly upright, almost boastful. That was a problem, but not too surprising. The pigweeds showed their natural agility.

Stanley Culpepper, University of Georgia Extension weed specialist, says scientific evidence collected this year and last confirms Georgia now has a concerning population of pigweed resistant to PPO-inhibitor Group 14 herbicides. PPO-resistance has been confirmed in other Southern states.

The plants in the greenhouse were part of a test Culpepper’s graduate student, Taylor Randell, conducted. Seven days prior, one set of plants, which were emerged at the time, was hit with a 125-ounce rate of Cobra with a crop oil concentrate. Another set, again already emerged, received a 240-ounce rate of Blazer with a nonionic surfactant. Another set got a 240-ounce rate of Reflex with a nonionic surfactant. Though stunted compared to the check plants, the tested plants looked OK and ready to continue growth.

Pre-emergence, residual herbicides — including PPO products — remain the best frontline defense if activated timely for a sound management program, he said, but the greenhouse study throws caution flags.

“If we get tolerance, or lose PPOs with our residuals, we will be in big trouble. That is not a place we want to be,” he said.

Research to determine how the pigweed in the greenhouse will respond to residual PPO activity began in November, he said.

Labels Back

With an EPA decision in October, cotton and soybeans growers again have access to use in-season dicamba technologies through 2025. Regulatory access to the technology again is a good thing, he said. Without continued sound weed management decisions, however, the technologies could play out before the labels expire or a court ruling stops them again.

The pigweed has proven again and again its naturally built to outmaneuver herbicides. One pigweed female competing with cotton for the entire season can produce 250 grams of seed, ready to be picked up and blown to the wind. Through natural selection, what if that one female is resistant to dicamba or 2,4-D? Pigweed resistance to dicamba and 2,4-D has been confirmed in Kansas, he said.

Culpepper has a picture he uses to make a point in some Extension presentations. It shows a spot in a field where emerged pigweeds were hit with Roundup plus dicamba. The pigweeds lay dead. But one stands firm, rigidly upright, almost boastful. That picture, he says, says it all.

The lone pigweed survives application of Roundup and dicamba in a Georgia field. (University of Georgia Extension)

Numbers Game

It’s a numbers game, and the numbers are in the pigweed’s favor. Studies in Georgia and Tennessee confirm residuals at planting when activated can provide almost 98% control of season-long pigweed management. That’s impressive but that 2% of escapes can total as many as 19,000 pigweed plants per acre that a post application must eliminate, or “pigweed can still eat your lunch,” he said.

Cover crops can further reduce the number of pigweed plants a post application must eliminate. A cover biomass of 4,500 pounds per acre works well but 7,000 pounds per acre works even better to suppress pigweed emergence.

Cotton growers know the mantra, he said, but it is always worth repeating:

  • Pigweed-free at planting
  • Residuals at planting with two effective active ingredients.
  • Sequential post-emergence application.
  • Layby with directed or hooded application.
  • Remove escapes.

The game against herbicide resistance is not going to get easier. Growers carry much of the burden against weed resistance and have done an exceptional job over a relatively short period of time to regain solid ground against pigweed. But resistance is an industry-wide issue. Crop protectant companies, academia and growers, along with science-strong regulatory policy decisions, will need to coordinate resources and information to stay ahead.

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From: EurekAlert

Contact: David Orenstein
Brown University

iceplant 79961_rel
IMAGE: An iceplant, from a region of high diversity in South Africa, is overtopping and killing a native shrub on the New Zealand coast, a region with far less diversity.



PROVIDENCE, R.I. [Brown University] — Dov Sax of Brown University and Jason Fridley of Syracuse University aren’t proposing a novel idea to explain species invasiveness. In fact, Charles Darwin articulated it first. What’s new about Sax and Fridley’s “Evolutionary Imbalance Hypothesis” (EIH) is that they’ve tested it using quantifiable evidence and report in Global Ecology and Biogeography that the EIH works well.

The EIH idea is this: Species from regions with deep and diverse evolutionary histories are more likely to become successful invaders in regions with less deep, less diverse evolutionary histories. To predict the probability of invasiveness, ecologists can quantify the imbalance between the evolutionary histories of “donor” and “recipient” regions as Sax and Fridley demonstrate in several examples.

Darwin’s original insight was that the more challenges a region’s species have faced in their evolution, the more robust they’ll be in new environments.

“As natural selection acts by competition, it adapts the inhabitants of each country only in relation to the degree of perfection of their associates,” Darwin wrote in 1859. Better tested species, such as those from larger regions, he reasoned, have “consequently been advanced through natural selection and competition to a higher stage of perfection or dominating power.”

To Sax and Fridley the explanatory power of EIH suggests that when analyzing invasiveness, ecologists should add historical evolutionary imbalance to the other factors they consider.

“Invasion biology is well-studied now, but this is never listed there even though Darwin basically spelled it out,” said Sax, associate of ecology and evolutionary biology. “It certainly hasn’t been tested before. We think this is a really important part of the story.”

Evidence for EIH

Advancing Darwin’s insight from idea to hypothesis required determining a way to test it against measurable evidence. The ideal data would encapsulate a region’s population size and diversity, relative environmental stability and habitat age, and the intensity of competition. Sax and Fridley found a suitable proxy: “phylogenetic diversity” (PD), an index of how many unique lineages have developed in a region over the time of their evolution.

“All else equal, our expectation is that biotas represented by lineages of greater number or longer evolutionary history should be more likely to have produced a more optimal solution to a given environmental problem, and it is this regional disparity, approximated by PD, that allows predictions of global invasion patterns,” they wrote.

With a candidate measure, they put EIH to the test.

Using detailed databases on plant species in 35 regions of the world, they looked at the relative success of those species’ invasiveness in three well-documented destinations: Eastern North America, the Czech Republic, and New Zealand.

They found that in all three regions, the higher the PD of a species’ native region, the more likely it was to become invasive in its new home. The size of the effect varied among the three regions, which have different evolutionary histories, but it was statistically clear that plants forged in rough neighborhoods were better able to bully their way into a new region than those from evolutionarily more “naive” areas.

Sax and Fridley conducted another test of the EIH in animals by looking at cases where marine animals were suddenly able to mix after they became united by canals. The EIH predicts that an imbalance of evolutionary robustness between the sides, would allow a species-rich region to dominate a less diverse one on the other side of the canal by even more than a mere random mixing would suggest.

The idea has a paleontological precedent. When the Bering land bridge became the Bering Strait, it offered marine mollusks a new polar path between the Atlantic and Pacific Oceans. Previous research has shown that more kinds of mollusks successfully migrated from the diverse Pacific to the less diverse Atlantic than vice-versa, and by more so than by their relative abundance.

In the new paper, Sax and Fridley examined what has happened since the openings of the Suez Canal in Egypt, the Erie Canal in New York, and the Panama Canal. The vastly greater evolutionary diversity in the Red Sea and Indian Ocean compared to the Mediterranean Sea and the Atlantic led to an overwhelming flow of species north through the Suez.

But evolutionary imbalances across the Erie and Panama Canals were fairly small (the Panama canal connects freshwater drainages of the Atlantic and Pacific that were much more ecologically similar than the oceans) so as EIH again predicts, there was a more even balance of cross-canal species invasions.

Applicable predictions

Sax and Fridley acknowledge in the paper that the EIH does not singlehandedly predict the success of individual species in specific invasions. Instead it allows for ecosystem managers to assess a relative invasiveness risk based on the evolutionary history of their ecosystem and that of other regions. Take, for instance, a wildlife official in a historically isolated ecosystem such as an island.

“They already know to be worried, but this would suggest they should be more worried about imports from some parts of the world than others,” Sax said.

Not all invasions are bad, Sax noted. Newcomers can provide some ecosystem services — such as erosion control — more capably if they can become established. The EIH can help in assessments of whether a new wave of potential invasion is likely to change the way an ecosystem will provide its services, for better or worse.

“It might help to explain why non-natives in some cases might improve ecosystem functioning,” Sax said.

But perhaps Darwin already knew all that.


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Dust blows tumbleweeds against a fence east of the Comanche Power Plant near Pueblo, Colo. Chris McLean/The Pueblo Chieftain/AP

P. Solomon Banda,
Associated Press


Mini-storms of tumbleweed have invaded the drought-stricken prairie of southern Colorado, blocking rural roads and irrigation canals, and briefly barricading homes and an elementary school.

Firefighters even had to cut a path through them to get to a pregnant woman who feared she’d be trapped in her home if she went into labor.

The invasion of the tumbleweed, an iconic symbol of both the West’s rugged terrain and the rugged cowboys who helped settle it, has conjured images of the Dust Bowl of 80 years ago, when severe drought unleashed them onto the landscape.

“It never ends,” said Chris Talbott, as he used a snow shovel to push the weeds off his lawn into a stack on the street in Colorado Springs.

The latest drought, which began in 2010, has created tumbleweed trouble in parts of New Mexico, Oklahoma and Texas. Desiccated Russian thistle, a woody leafy plant, and kochia, both invasive weeds from Eurasia, are the culprits.

In Colorado, herds of cattle would eat the tumbleweed, helping to keep it in check, but many ranchers in recent years have reduced or gotten rid of their animals because of the drought. After the first winter freezes in November, the plants broke loose and began rolling with the wind.

“They looked like sheep running across the prairie because the whole prairie was alive,” Ordway rancher Doug Tecklenburg said of a March 15 wind storm. He’s taken to driving with a pitch fork in his truck to get through clogged roads.

For municipal authorities, there’s a big price tab for that tumbleweed.

Crowley County, high plains country of ranching and farming east of Pueblo in southern Colorado, has spent $108,000 since November — more than a third of its annual budget — clearing roads and bridges of tumbleweed to make sure residents and emergency vehicles can move.

It’s labor-intensive work. “Gathering tumbleweeds is like gathering kindergarteners with a bunch of balloons and trying to keep them in one location,” said Russell Bennett, a county roadman employed by Crowley County.

El Paso County, which includes Colorado Springs, has spent $209,000.

Aside from the roads, the tumbleweeds have buried cars and blocked houses in new developments on the outskirts of Colorado Springs.

Officials have tried to attack the tumbleweed with snow blowers and rotary attachments on tractors used to cut crops like alfalfa. They’ve even tried to bale it for cow feed. But the wiry, springy weed clogs machinery, and baling is too expensive to be economical.

Given the cost, at least three Colorado counties — El Paso, Crowley and Pueblo — are considering local states of emergency that would allow them to seek financial help from the state.

At his county commission office, Allumbaugh played for a reporter a song called “Tumbling Tumbleweeds” — popularized by Gene Autry’s 1935 film of the same name — and said that people often think of it as they dismiss tumbleweeds as a harmless bit of nostalgia of a wide-open West.

He said he has even drawn snickers when he mentions that the county has a “tumbleweed emergency.”

“What we have is not funny,” he said.


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