Archive for the ‘Weeds’ Category


LSU AgCenter weed scientist Daniel Stephenson holds a ragweed parthenium plant Photo by Olivia McClure/LSU AgCenter
LSU AgCenter weed scientist Daniel Stephenson holds a ragweed parthenium plant at the annual field day at the Dean Lee Research and Extension Center in Alexandria on July 13, 2017.

False ragweed becoming major row-crop pest in Louisiana

Ragweed parthenium (also know as false ragweed) has gone from a nuisance in pastures to a major pest in Louisiana row crops.

Bruce Schultz 1, Olivia McClure | Jul 18, 2017

An LSU AgCenter weed scientist speaking at a field day on July 13 at the Dean Lee Research and Extension Center warned farmers about ragweed infestations in their fields.

The scientist, Daniel Stephenson, said ragweed parthenium has gone from a nuisance in pastures to a major pest in Louisiana row crops. Ragweed parthenium is also known as false ragweed.

 The weed can become a major problem quickly if it is not controlled early. Ragweed parthenium often germinates after spring burndown herbicide applications and is not discovered until after crops have emerged, Stephenson said.

Applications of certain herbicides prior to or at planting can provide control of an existing population, he said.

Current research shows that after crop emergence, control options are limited, but Stephenson recommended sequential applications of either Liberty, Liberty plus Roundup PowerMax, or Roundup PowerMax plus a half pound per acre of dicamba.

Stephenson said it’s likely the weed has been spread by equipment.“Ragweed parthenium is a very troublesome weed that is difficult to control with herbicides,” he said. “If a producer sees it in their field, they need to remove it.”

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July 13, 2017

The photo is from https://doi.org/10.1017/wsc.2017.14. It shows one of the plants that come from a population that apparently adapted to taller crops and is GR and another that comes from a population adapted to smaller crops and is GS. Additionally, below you can see a few examples of the great diversity in morphology that we found among Palmer amaranth populations. – Credit: Photo by Ramon Leon

Palmer amaranth is widely considered to be one of the most damaging and difficult to control agricultural weeds in North America. A lot of time and attention has been devoted to herbicide-resistant Palmer amaranth and the significant yield losses it can produce. Research featured in the journal Weed Science, though, shows other “life history” traits may be contributing to crop losses by making Palmer amaranth more aggressive and difficult to control.

Researchers from the University of Florida collected samples of Palmer amaranth from 10 fields in Florida and Georgia. The sites had widely divergent cropping histories – from short-statured vegetables and peanut crops to tall corn and cotton crops. The fields also varied in herbicide use. Some were devoted to organic production, while others had a history of intensive herbicide use.

Significant differences were observed in the traits of the Palmer amaranth from the various fields, such as fresh and dry weight, days to flowering, plant height, leaf shape and canopy. Researchers say these differences could not be explained by whether the Palmer amaranth population was glyphosate resistant or glyphosate susceptible. Instead, crop rotation and crop canopy better explained the many variations found. For example, the tallest populations of Palmer amaranth came from corn fields, while the shortest came from fields planted with the shortest crops.

“It appears Palmer amaranth can evolve life-history traits that increase its potential to grow and reproduce in various cropping systems,” says Ramon Leon, Ph.D., a member of the research team. “To avoid the development of more aggressive weed biotypes, it is important to consider these evolutionary consequences when designing crop rotation systems and weed management strategies.”

Full text of the article “Differentiation of Life-History Traits Among Palmer Amaranth Populations (Amaranthus palmeri) and its Relation to Cropping Systems and Glyphosate Sensitivity” is now available in Weed Science Vol. 65, Issue 3, July-September, 2017.


More news from: Cambridge University


Website: http://www.cam.ac.uk

Published: June 13, 2017

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2 PPOresistant pigweeds confirmed in Arkansas Tennessee MidSouth weed specialists have been warning that pigweeds ndash already often resistant to multiple chemistries ndash were in danger of developing resistance to PPO chemistry Those warnings have proven prophetic

The resistance treadmill – how do we get off?

Weed scientists say we can’t keep replacing one resistant herbicide with another.

Forrest Laws | May 12, 2017

How long will it take Palmer amaranth to become resistant to the new formulations of dicamba and 2,4-D that have been approved to be applied over the top of dicamba- and 2,4-D-tolerant cotton and soybeans?

That depends on what growers do to protect the new technologies, according to Bob Scott, a University of Arkansas Extension weed scientist and a speaker at the Pigposium 3 herbicide resistance meeting in Forrest City, Ark.

“If we follow on the resistance path that we’ve been following, and we just come in here and add dicamba to take care of this problem (PPO inhibitor resistance), what do you think is going to happen?” Dr. Scott asked. “We’re just going to add to our list of resistant weeds. We’re going to add dicamba to the growing list of resistance.”

Dr. Scott traced the history of the development of herbicide resistance in Palmer amaranth or pigweed in soybeans, beginning with Prowl and Treflan in the 1980s, the ALS herbicides such as Scepter in the 1990s, glyphosate in the 2000s and

the PPO inhibitor herbicides such as Reflex and Flexstar since 2010.Extension weed scientists at the University of Arkansas have already demonstrated how quickly resistance could develop to dicamba, the active ingredient in the new Xtendimax, Engenia and FeXapan herbicide formulations.

Three generations

“We proved this in a laboratory where this particular population of pigweed in just three selections using sub-lethal doses was not controlled with 16 ounces of dicamba,” Dr. Scott noted. “So we just proved that it can happen if we don’t do something to address herbicide resistance, and we’re not proactive in managing this from Day one.”

He had some words of warning about glufosinate or Liberty, which is one of the few remaining herbicides that can be applied postemergence to control pigweed – in Liberty Link cotton and soybeans.

“The last herbicide that’s put on the field is where the selection pressure occurs,” he said. “I had somebody ask me the other day about planting Liberty Link beans and putting Prefix or Zidua down and using Liberty post. But that last application they’ve been putting out has always been Liberty post, right?

“So they said ‘Is that a good enough reason to rotate to Xtend beans?’ and I said ‘absolutely.’ It’s a good reason to rotate chemistry. If it’s been working, change it. We have to rotate to change that last selection pressure that goes on that field.”

Farmers in northeast Arkansas have about a 50 percent chance of encountering resistance to PPO inhibitor herbicides in their fields in 2017, according to Jason Norsworthy, professor of weed science at the University of Arkansas and one of the organizers of the Pigposium.

Multiple resistance

But some growers are having to deal with Palmer amaranth populations that are not only resistant to PPO inhibitors but to three other groups of herbicides, as well, said Dr. Norsworthy, who holds the Elms Farming Chair of Weed Science at the U of A.

“In 2015, this field near Gregory in Woodruff County was found to contain resistance not only to the PPO inhibitor or Group 14 herbicides, but also to the ALS chemistries (Group 2), the dinitroanilines, things like Treflan and Prowl (Group 3), and Roundup (glyphosate – Group 9,” he said, referring to a field overgrown with pigweed.

“This was actually a conventional soybean field. Bob Scott did research in this field in 2015. And when you take a look at this population, we’re unable to grow Roundup Ready or conventional soybeans in this field because there is no effective postemergence option for the control of a pigweed population that has PPO resistance as well as glyphosate resistance.”

Weed scientists have now documented resistance in Palmer amaranth to the PPO inhibitor class of herbicides in seven states – Arkansas, Mississippi, Tennessee, Missouri, Illinois, Kentucky and Indiana. Norsworthy said 19 counties in Arkansas have confirmed PPO resistance.

“If you had any Palmer amaranth in one of your fields at harvest in 2016, you have better than a 50 percent chance that you have PPO-resistant Palmer in your fields,” said Dr. Norsworthy. “Folks, this is spreading, and it is spreading no different than what we saw with glyphosate. We are quickly losing one of the mainstays, especially in soybeans, from a weed control standpoint.”

Better than 50 percent

He displayed a slide of a bench top containing plants from about 40 different populations of Palmer amaranth. The plants were sprayed with 1.5 pints of Flexstar when they were about 1-inch tall.

“Anything you see that is still alive on this bench top (40 to 50 percent of the plants) would be resistant to the PPO chemistry,” he said. “Research has been conducted that shows the resistance mechanism is very similar to what you see in waterhemp in the Midwest. However, there are other PPO resistance mechanisms in this population that are much more resistant to the PPO chemistry than in some of the other pigweeds out there like waterhemp.”

Dr. Scott said that once resistance occurs that herbicide is lost to producers whether it’s glyphosate, Treflan or Flexstar.

“There’s no fitness penalty for the most part,” he said. “Some resistances have fitness penalties – the weed is damaged by the herbicide so it’s less competitive – but in pigweed it just seems to make it stronger the more resistant it gets.”

The threat of multiple resistance or resistance to more than one class of chemistry is frightening, Scott says. “I’ve had people calling me wanting to know where they can buy a good hoe, and that’s not my idea of weed science.”

Change it if it’s working

He said overlapping residual herbicides, rotating chemistries – even when the current herbicide is working – and using cultural practices will all be needed to preserve any new chemistries or traits growers may get in the years ahead. And growers need to treat the new traits – Xtend, Enlist and the new Balance trait that is expected to be approved in the near future – as if they were new herbicide chemistries.

Dr., Scott also called on herbicide manufacturers to help growers “do the right thing” economically when it comes to helping growers avoid overusing the currently available herbicide tools.

To read more about herbicide resistance-fighting efforts, click on http://www.deltafarmpress.com/cotton/odds-not-arkansas-growers-favor-ppo-herbicides-2017

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Iowa farmer

2017-05-06T20:00:00Z Non-herbicide tactics help manage weeds Iowa Farmer Today
May 06, 2017 8:00 pm

Editor’s note: The following was written by Lizabeth Stahl, Jared Goplen and Lisa Behnken, University of Minnesota Extension educators, for the university’s Minnesota Crop News website.

Weed management tools can be divided into three main categories: mechanical, cultural and chemical. Historically in conventional systems, chemical control options, or herbicides, have been relied on heavily.

Herbicide-resistant weed populations, however, are limiting herbicide options and effectiveness in many fields. Implementing non-chemical options, such as cultural and mechanical control tactics, can help make weed management systems more effective and durable.

To develop a more robust weed management program, consider the following three key strategies:

Account for weed emergence patterns

Weed emergence is driven by a number of factors, including temperature, light, nitrogen and/or chilling period, depending on the species.

University of Minnesota trials at Waseca in 2016 showed that delaying soybean planting until May 19 resulted in pre-plant tillage removing nearly 49 percent of the giant ragweed that emerged over the season. Soybean yield potential was still around 94 percent of optimal at the May 19 planting date, based on long-term research results, and the benefit was a much lower population of giant ragweed to control post emergence.

Soybean yield potential of the early planting date averaged 99 percent of optimal, however, pre-plant tillage removed less than 8 percent of the giant ragweed emerged over the season.

Pre-plant tillage can be an effective weed control tool, especially when planting is delayed. Flushes of early-emerging weeds, such as giant ragweed, common lambsquarters and winter annuals, can be taken out with pre-plant tillage, but be sure tillage is aggressive enough to destroy the weeds, and not just uproot and transplant them.

In contrast, waterhemp emerges later in the season, typically emerging over an eight to 10 week time period. This is why residual herbicides or the layering of residual herbicides (e.g. an application at planting and then 30 days later) is recommended for control of waterhemp.

Manage the weed seedbank

Seed production of weeds can vary significantly by species. Giant ragweed, for example, has been found to produce from 1,800 to 10,000 seeds per plant, while waterhemp can average over 350,000. Although competition with other plants can reduce seed production, dense weed populations have the potential to produce tremendous amounts of weed seed.

Common lambsquarter is a long-term survivor in the weed seedbank, and according to the University of Michigan, it takes an estimated 78 years to see a 99 percent depletion of the seedbank.

In contrast, University of Minnesota research demonstrated the giant ragweed seedbank could be depleted 97 percent in two years. University of Illinois research found the waterhemp seedbank could be depleted by more than 99 percent in 4 years.

Burial of seed by tillage can increase longevity in the seedbank, while seed left on the soil surface can be lost to predation and decay. For this reason, delaying tillage as long as possible in areas where weeds went to seed could help reduce long-term weed management challenges. Avoid deep tillage, which enhances seed longevity.

Not running the combine through a weed patch will help limit the spreading of weed seeds throughout the field. Also, manage weeds along field edges to help prevent buildup of the weed seedbank.

Incorporate sound agronomic tactics

Ensuring the crop is as competitive as possible (e.g. adequate fertility, planting population and disease and pest control) can help enhance weed control. Narrow rows, expanding crop rotations and cover crops have the potential to aid in weed control as well.

Cultivation is another effective tool, allowing you to remove weeds without setting back the canopy as some postemergence herbicides can, leading to faster canopy closure and a more competitive environment for weeds.

Cultivation was evaluated in Minnesota research trials in 2015 and 2016. A preemergence application of Boundary was followed by either Liberty or mechanical cultivation. In 2016, final waterhemp control was significantly better with the Boundary/Cultivation treatment (98 percent) compared to the Boundary/Liberty program at 89 percent.

Copyright 2017 Iowa Farmer Today. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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USAID logo                                            IPM IL Logo

Parthenium hysterophorus L. is a native plant of tropical and sub-tropical South and North America that adversely affects food security, biodiversity, and the health of both humans and livestock in East Africa. In East Africa, Parthenium reduces the yield of many major crops such as sorghum and corn, competes with preferred pasture species, and, when consumed by domestic animals, taints their milk and meat, thereby reducing their value. It also causes human health problems such as severe contact dermatitis and respiratory problems. In addition, because of its ability to release toxic chemicals, Parthenium can replace natural vegetation, thus adversely affecting plant biodi­versity.


Zygogramma bicolorata, a leaf-eating beetle on Parthenium

In July, Zygogramma bicolorata, a leaf-eating beetle that feeds on Parthenium, was released at several sites around Wollenchiti, Ethiopia. The sites included a farmer`s field, a big uncultivated and a fenced area nearby a railway. The released Zygogramma, especially the second generation, has begun causing damage to Parthenium in cultivated as well as in non-cultivated areas. We are encouraged by the rapid establishment and spread of Zygogramma. Wollenchiti this year received heavy rain and that resulted in lush growth of Parthenium, which is ideal for the bioagent. Fencing the release plots also allowed Zygogramma to have adequate time to build its population before spreading to surrounding fields.

Zygo release site Site 4 Sept. 7 2016.jpg

Zygogramma defoliated Parthenium in foreground. Near Wollenchiti, Ethiopia, September 7, 2016.


Zygogramma defoliated Parthenium  (brownish plants beside fence)

This release was done through the “Biological control of the invasive weed Parthenium hysterophorus in East Africa” project led by Virginia State University, which has been awarded a grant of $748,465 by USAID through the Integrated Pest Management Innovation Lab managed by Virginia Tech. The goal of the project is to build on the accomplishments of the two previous USAID IPM IL-funded Parthenium projects to abate the spread and impact of the weed in east Africa. One of the objectives of the project is to scale-up the rearing and release of approved biocontrol agents, Zygogramma along with the stem boring Listronotus setosipennis in Ethiopia.

Wondi Mersie, Ph.D.

Associate Dean and Director of Research

Virginia State University

Petersburg, VA 23806





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Diversity disrupts evolution: The future of global weed management


 More services15
  Updated 14 Sep 2016, 3:38am

With a declining amount of chemical innovation in the weed management industry, it is expected a mix of technology, farming practices, and herbicides will be the keys to the future of weed management.

Diversification was the message at the 20th Australasian Weeds Conference in Perth this week, with growers facing increasing weed resistance to herbicides, and an industry that has not been able to keep up.

There has been a decrease in patent filings and product launches, and no new modes of action for over 20 years in the herbicide industry — but this does not discourage head of weed control research for Bayer Crop Science, Dr Marco Busch.

“I’m really excited about the opportunities,” Dr Busch said.

“If you identify the issue, you can do something about it.”

And for Bayer Crop Science, that means the development of new products — a process which can take up to 10 years.

So what can be done to tackle herbicide resistance in the meantime, and for the future?


“Herbicides are not the only tool the farmers have at their hand, there are all those agronomical tools,” Dr Busch said.


With technology advancing, new tactics are required to provide longevity to the current and future herbicides on the market.

General manager of crop protection for the Grains Research and Development Corporation, Dr Ken Young, believes the Australian grains industry is “at the beginning of a new dawn” where growers are becoming more receptive to incorporating new tactics into their farm plan.

“That can be crop cultivation, through to cultural management through row spacing, row orientation, through to the new technologies that are coming through where they can use microwaves or targeted tillage to control their weeds,” Dr Young said.

Dr Young believed the increasing cost of weed management in the Australian grains industry was the catalyst for this “new dawn”.

“In the past, herbicides have worked extremely well, and been very cost effective, very cheap relatively,” he said.

“And it’s only until that system’s not working we have to look for other answers, and that’s what the case is.”

Earlier this year the GRDC commissioned a report into the cost of weeds, and found there had been a “huge increase of the costs of managing resistant weeds”, to $3.3 billion annually in expenditure and yield loss, costing Australian grain growers an average of $146 per hectare.

“Growers look at that additional cost and say ‘what else can I use to manage that? And if I’ve got to pay an extra $60 a hectare to manage my weeds, what can I use that $60 for? Is it best of using a herbicide? Or is it best of using harvest weed seed management to do it, and getting longevity of my herbicides as well?’,” Dr Young said.

Australian innovations competing internationally

Compared to our overseas counterparts, Australia is thought to shape up relatively well when it comes to innovation in weed management.


Director of the Australian Herbicide Resistance Initiative (AHRI), Professor Stephen Powles, believes this comes down to necessity: where there are issues, there is innovation.

“We’ve had to be [leaders], because of the massive herbicide resistance problems we’ve had,” Professor Powles said.

“And as a result, we’ve developed some technologies in Australia that have not been developed elsewhere.

“Especially what we call ‘harvest weed seed control’ (HWSC).”

Professor Powles said most Western Australian farmers were using a form of HWSC, which targeted weed seeds during harvest to minimise the seed bank.

“We all should be proud of that work that’s been home grown Australian research,” he said.

“Our agronomists are very good, our farmers are very, very good, our farmers are excellent farmers, so we’ve got a lot to be proud of in the area.”

However despite home-grown developments such as HWSC, Professor Powles believes Australia will remain reliant on technology developed overseas.

“The herbicides that are used here are not developed here, they’re developed by the small number of corporations because of the huge research effort that’s required,” he said.

“It’s a combination of international technology and how to make it work in Australia.”

Topics: weeds, crop-harvesting, agricultural-chemicals, agricultural-crops, perth-6000

First posted 14 Sep 2016, 3:06am

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