- Author: Ben Faber
Conditions are right for weeds
Early rain combined with unseasonable heat this week makes for ideal conditions for weeds,well, everywhere!Get ahead of the menace with these UC guides to weed control. For gardeners growers, range managers, just about everyone!
Act quickly-these prices end February25!
This encyclopedic yet easy-to-use2-volume set covers 262 individual entries, including a full description of 451 species and another 361 plants compared as similar species, representing 63 plant families. Includes a CD of every photograph in the book--perfect for your presentation slide deck.
Showprice:$40.00-Save over 35%!
- Author: Gale Perez
Our friend Lynn Sosnoskie (at Cornell University) shared the following announcement with us:
A free (downloadable) resource
Manage Weeds on Your Farm – A Guide to Ecological Strategies
“I am most pleased to share the good news that our long-awaited SARE-sponsored book “Manage Weeds on Your Farm – A Guide to Ecological Strategies” by the late Chuck Mohler, John Teasdale, and me has now been published online and is freely available for download from the SARE website link below. This is a great resource that took Chuck and I (and many student assistants) numerous years to complete. The coming onboard of John Teasdale as a co-author during the last two years was enormously helpful especially given Chuck's failing eyesight and his untimely passing.”--Toni DiTommaso, Professor and Chair, School of Integrative Plant Science Soil and Crop Sciences Section, Cornell University
ABOUT THE AUTHORS
PART I CONCEPTS OF ECOLOGICAL WEED MANAGEMENT
CHAPTER 1 INTRODUCTION
- Purpose and Philosophy
- How to Use This Book
CHAPTER 2 HOW TO THINK ABOUT WEEDS
- What is a Weed?
- The Origins of Weeds
- Weed Populations are Dynamic
- Weed Density Affects Weed Death and Reproduction
- Vegetative Propagation of Perennial Weeds
- Seed Weight
- Seed Germination: Why Tillage Prompts Germination
- Season of Weed Emergence
- Seed Longevity
- Depth of Seedling Emergence from the Soil
- Growth and Competition for Light
- Photosynthetic Pathway
- Sensitivity to Frost
- Drought Tolerance
- Nutrient Use
- Response to Soil Physical Conditions
- Response to Shade
- The Timing of Reproduction
- The Magnitude of Reproduction
- Natural Enemies
CHAPTER 3 CULTURAL WEED MANAGEMENT
- Many Little Hammers
- Crop Rotation and Weed Management
- Crop Competitiveness
- Cover Crops
- Organic Mulch
- Continuous No-Till Vegetable Production Using Organic Mulches
- Synthetic Mulch
- Weed Management During Transition to Organic Production
- Natural Product Herbicides
- Livestock for Weed Management
- Preventive Weed Management
- Preventing the Arrival of New Weed Species
CHAPTER 4 MECHANICAL AND OTHER PHYSICAL WEED MANAGEMENT METHODS
- Essential Concepts of Mechanical Weed Management
- Types of Tillage and Their Effects on Weeds
- Using Tillage Against Perennial Weeds
- Tillage Effects on Weed Seedling Density
- Ridge Tillage
- Tilled Fallow
- Stale Seedbed
- Principles of Mechanical Weeding
- Cultivators and Cultivating Tools
- Other Physical Weed Control Devices
- Cultivator Guidance Systems
- Matching the Implement to the Task
- Hoeing Weeds
- Cultivation and Tillage in the Dark
- Soil Tilth and Cultivation
- Energy Use in Physical and Chemical Weed Management
CHAPTER 5 PROFILES OF FARMS WITH INNOVATIVE WEED MANAGEMENT PRACTICES
- The Martens, Penn Yan, N.Y.
- Paul Mugge, Sutherland, Iowa
- Eric and Anne Nordell, Trout Run, Penn.
- Scott Park, Meridian, Calif.
- Carl Pepper, O'Donnell, Texas
PART II MAJOR AGRICULTURAL WEEDS OF THE UNITED STATES AND CANADA
- How the Species Chapters Were Developed How to Find Ecological Information and Develop a Management Plan for Species not Covered in this Book
WEED CHARACTERISTICS SUMMARY TABLES
GRASS WEEDS AND THEIR RELATIVES
- Annual bluegrass
- Downy brome
- Fall panicum
- Italian ryegrass
- Large crabgrass
- Purple nutsedge
- Wild garlic
- Wild oat
- Wild-proso millet
- Yellow nutsedge
BROADLEAF WEEDS AND THEIR RELATIVES
- Annual sowthistles
- Canada thistle
- Catchweed bedstraw and false cleavers
- Common chickweed
- Common cocklebur
- Common groundsel
- Common lambsquarters
- Common milkweed
- Common purslane
- Common ragweed
- Common sunflower
- False cleavers (see “catchweed bedstraw and false cleavers”)
- Field pennycress
- Giant ragweed
- Hemp sesbania
- Palmer amaranth
- Perennial sowthistle
- Prickly lettuce
- Prickly sida
- Wild buckwheat
- Wild mustard
- Wild radish
- Yellow woodsorrel
- Author: Rebecca Ozeran
In the 5 years I've been with UCCE, I have received a few recurring weed-related questions. I've certainly had some unique requests, like how to deal with fig trees invading a livestock water pipeline, or whether filaree might be harmful to guinea pigs (it isn't). But often, questions I receive about rangeland or pasture weeds fit under three categories:
- Is this plant toxic to my animals?
- How can I get rid of yellow starthistle?
- What can I plant in my pasture to outcompete all these weeds?
Of course, each question has its own “It depends”-style answer. But today, I want to share the resources I recommend for these Frequently Asked Questions.
Is this plant toxic? (Usually following the question, “What is this plant?”)
- Toxicity varies with plant species, growth stage, part or structure (e.g leaf versus flower) and relative abundance. Toxicity also varies with animal species and size, and what other feed is available. Some plants are toxic at all growth stages and in all parts of the plant (such as oleander) while other plants accumulate toxins at certain times of their growth cycle (such as plants that accumulate nitrate) or affect livestock species differently (such as yellow starthistle).
Fiddleneck, like oleander, accumulates toxins in all plant parts, though the concentration can vary. Fiddleneck seeds and flowers often contain the highest concentrations of alkaloids within a single plant.
- Fortunately, we have an excellent guide that describes common toxic plants and how to reduce risk to your animals: Livestock-Poisoning Plants of California. For plants that aren't listed, you can always contact your local farm advisor for assistance in plant identification and management! If you suspect plants are poisoning your animals, please contact your veterinarian ASAP.
How can I get rid of yellow starthistle?
- While we probably can't eliminate it completely,yellowstarthistle can be managed to reduce its impact on landscapes and livestock. Several usefulresourcesdescribeyellowstarthistle management, and can be freely accessed or downloaded:
- UC IPM Pest Note on Yellow Starthistle, a brief overview of the plant itself and key management strategies
- Yellow Starthistle Management Guide, published through Cal-IPC, probably the most thorough document on yellow starthistle impacts and management tools
- Yellow Starthistle weed report, from Weed Control in Natural Areas in the Western United States, especially handy if you want a concise comparison of management options, or something that is well formatted for printing out
What do I plant to manage pasture weeds?
- Maintaining healthy forage cover is one of the best ways to reduce weed pressure in a grazing or haying area, whether irrigated or not. However, getting good forage established can be more challenging when there are weeds already present. Drought years like this year don't help, either – many deep-rooted broadleaf weeds are doing fine while desirable grasses had a shorter than usual growing season. And, of course, site-specific variations affect what forage plants might be competitive, and what weeds they might have to outcompete.
- Because the answer is more complicated than “buy X seed mix”, I usually refer to the excellent guide, Establishing and Maintaining Irrigated Pasture for Horses. The principles of pasture preparation, including strategies for weed management during pasture establishment, are similar across grazing livestock species. Most of the information in the guide can also apply to dry pastures aside from the specific sections about planning and using irrigation.
Healthy pastures will better outcompete weeds. The species in that pasture will vary across the state. Having sufficient moisture - from rain or irrigation - also impacts weediness!
Now, range and pasture weed questions aren't going to be completely resolved by a single blog post – but I do hope this post is a helpful starting point for anyone who manages rangelands or pastures.
If you have a question that isn't listed in this short FAQ, feel free to reach out! I'm happy to expand this resource. You can comment on this blog, email firstname.lastname@example.org, or message through my program Facebook page.
Will Rising Temperatures Make Superweeds Even Stronger?
Widely used herbicides are struggling to kill some weeds. Some experts think heat could be part of the problem.
From the digital magazine, Undark • Dec. 7, 2020
By Natasha Gilbert • 12.07.2020
Around 10 years ago, in the fierce heat of the Kansas summer, many of the noxious kochia weeds invading Phillip Stahlman's research fields simply wouldn't budge when sprayed with a mixture of two widely used herbicides, glyphosate and dicamba. Just a few months earlier, in the cooler spring weather, the herbicide mixture had easily triggered the weed's small thin leaves to curl up and turn brown, signaling the plant's demise.
Now the stalwart weed had Stahlman stumped. Stahlman, then a weed scientist at Kansas State University, had never encountered this problem with herbicides before. He initially assumed that he had applied the agrichemicals incorrectly. But year after year, the same thing happened. Stahlman knew something was up. He kept a close watch on the weeds in his fields. He also conferred with local farmers who reported seeing similar problems. “The light didn't come on for a while until the issue kept reoccurring. It was like putting together a puzzle,” says Stahlman.
Eventually, Stahlman, who has since retired, decided that the problem was likely temperature: Something about spraying in high heat was rendering the herbicides less effective.
Stahlman is not alone in making this observation. Today, mounting evidence suggests that temperatures of around 90 degrees Fahrenheit or above can make some herbicide-resistant weeds even more resistant, and cause other weeds to be less sensitive to certain chemicals.
Some farmers say they know high temperatures can mess with some herbicides, so they try to avoid spraying in the heat of the day. “A good rule of thumb is if it's 85 to 90 degrees Fahrenheit, just don't spray,” says Curt Gottschalk, a farm manager in Hays, Kansas.
Not all experts agree that this pattern, largely demonstrated in lab experiments, poses a problem for farmers. And some herbicides appear to work even better at high temperatures. But if heat is boosting many weeds' resistance to major herbicides, the implications could be significant. Left unchecked, weeds can devastate harvests and income — if farmers didn't make an effort to control weeds, they could wipe out around half of all corn and soybean yields across the U.S and Canada, according to the Weed Science Society of America, a nonprofit society of academic and industry scientists. The loss could cost farmers around $43 billion annually.
Farmers are already battling against epidemics of weeds that have developed genetic resistance to multiple herbicides, including glyphosate and dicamba. Stahlman and other weed researchers argue that temperature could be an overlooked second factor strengthening weeds' defenses against herbicides. Although most farmers now understand that temperature affects herbicides, to the untrained eye it could look just like herbicide resistance, Stahlman says.
These researchers also fear the issue could worsen in the future as climate change raises temperatures and extreme weather events, including heat waves, become more frequent.
“We already know that herbicide resistance is the most problematic issue in chemical weed control,” Maor Matzrafi, a weed scientist at Israel's national Agricultural Research Organization, wrote in an email to Undark. “Maybe reduced sensitivity due to climate change is next in line.”
Farmers used to rely less on herbicides, instead controlling weeds using laborious methods such as tilling and manual removal. But, starting in the mid-1990s, biotechnology companies began debuting genetically modified crops that were resistant to common, powerful herbicides. The new seeds allowed farmers to liberally spray their fields with agrochemicals to kill weeds while their GM crop flourished. The technology made most manual weeding unnecessary, and herbicide use surged globally. But weeds evolved in response, and herbicide resistant varieties emerged. That has set off a new battle between farmers and weeds, with farmers increasingly using combinations of chemicals, as well as additional doses, to try to knock off weeds.
After Stahlman's experience with kochia weeds, though, he began to examine whether temperature could be affecting herbicide performance more than was widely recognized. (Stahlman, like many academic weed scientists, has received research funding from agrochemical companies in the past.)
To decipher how heat helps weeds fend off herbicides, Stahlman teamed up with KSU colleagues Mithila Jugulam, a weed physiologist, and Junjun Ou, a research assistant. The team grew seedlings from kochia populations that originated in Kansas, in chambers kept at temperatures ranging from 63.5 to 90.5 degrees Fahrenheit — representative of the state's spring and summer daytime heat. The temperature in the chambers dropped every 12 hours to mimic cooler nighttimes. When the seedlings reached around 4 inches high, the researchers dosed some with glyphosate and others with dicamba. At weekly intervals, the team examined the weeds for signs of injury. After one month, they cut down the weeds and dried and weighed them.
The team found that, at high temperatures, they needed more than twice the amount of glyphosate and dicamba to control weeds. They published their results in 2016.
“A good rule of thumb is if it's 85 to 90 degrees Fahrenheit, just don't spray,” says Curt Gottschalk, a farm manager in Hays, Kansas.
To understand why heat reduced sensitivity, the researchers tracked the herbicides' paths through the weeds using mildly radioactive versions of glyphosate and dicamba. The former previously manufactured by Monsanto, and the latter produced by BASF Corp. (BASF Corp. provided a graduate student assistantship to Ou for a different project.)
The team found that the leaves absorbed less glyphosate at higher temperatures. They're not sure why, but Jugulam thinks the heat may encourage the kochia to develop thicker cuticles — a protective layer on the leaf surface — which then boost the weeds' defenses against the herbicide. The team discovered a different process at work when the weeds encountered dicamba. Temperature did not affect the amount of dicamba that the weeds' absorbed, but it did hinder the herbicide's movement through the plant so that less reached its target — the tissue developing at the tips of new shoots and leaves.
In another study, published last year, Jugulam turned her attention to the herbicide 2,4-D, one of the ingredients of agent orange, an infamous defoliant used in the Vietnam War. Today, it's one of the most widely used herbicides. Jugulam tested how temperature affected the herbicide's ability to control common waterhemp, a broadleaf weed found encroaching on Midwestern corn and soybean fields.
In the tests, Jugulam examined some common waterhemp that had developed genetic resistance to 2,4-D, and some that had not. She found that it took more than three time as much herbicide to kill the resistant weed under hot, dry conditions than at cooler temperatures. She found a similar but smaller effect in the susceptible weeds.
Herbicide-resistant waterhemp survives exposure to 2,4-D by quickly breaking the chemical down into nontoxic substances before it can reach its targets at the tips of roots, stems, and leaves. When the temperature is high, Jugulam found, waterhemp breaks down those molecules faster.
Jugulam also noted that under high temperatures, some herbicide resistant weeds appear to become more resistant and some susceptible weeds may require more herbicide for their control.
Not all weeds and herbicides respond to temperature the same way. For example, Jugulam has also found that 2,4-D and glyphosate work better at higher temperatures against common and giant ragweed, two other weeds common in U.S. farmers' fields. Jugulam also says that, even in cases where heat does hinder herbicides, the impacts appear to be mostly limited to dry conditions. Areas with high humidity and rainfall might not see the same effects.
But some experts say evidence is growing in a variety of species and agrochemicals that temperature, and in some cases high carbon dioxide levels, affect weed control, at least in the laboratory.
In tests published in 2016, Matzrafi found that at high temperatures four different species of grass weeds stood up against diclofop-methyl, an ingredient in an herbicide manufactured by Bayer, significantly better than they did at lower temperatures. Matzrafi also found that high temperatures made another herbicide, pinoxaden, less able to curb growth of the invasive grass false brome. Moreover, the grass thrived even when it was switched from cooler conditions to a hotter environment up to two days after the herbicide treatment.(The research was partially funded by ADAMA Agricultural Solutions, an agrochemical company based in Israel.)
“Our findings, and many other studies since the ‘90s, suggest that post-application environmental conditions may also affect herbicide sensitivity,” explained Matzrafi in an email. Even if farmers spray during cooler temperatures, that might not be enough to avoid the effects of heat.
Those conditions, experts fear, will worsen under climate change. Already, many U.S. states important for agriculture, as well as other major food producing regions around the world, regularly experience temperatures topping 90 degrees Fahrenheit during growing seasons. Some researchers say that problems with heat and herbicide performance are coming to the fore now partly because of more frequent episodes of extreme heat over the past few decades.
However, it is hard to pin the effects seen today on recent climatic changes, Lewis Ziska, a plant physiologist at Columbia University in New York, wrote in an email to Undark. But, noting that weeds are “the greatest constraint for food production,” Ziska warns that “they will be a formidable challenge for farmers in a more extreme environment.”
In the Midwest, for example, temperatures could rise by an average of 8.5 degrees Fahrenheit by the end of the century, with longer and more frequent stretches of extreme heat, according to federal government projections. And in South Asia, including India — a globally important region for producing rice, pulses, nuts, and cotton — the Intergovernmental Panel on Climate Change projects that average annual temperatures will rise by nearly 6 degrees Fahrenheit by 2100.
In the first experiment of its kind, the results of which were reported last year, Matzrafi studied the joint effect of heat and raised carbon dioxide levels on two different weed species and found that the combination boosts weeds' herbicide defenses beyond that by either factor alone.
It's not clear whether herbicide manufacturers are prepared for the coming challenges of a warming planet. Many do not recommend optimal spraying temperatures to ensure efficacy in the guidelines they distribute to farmers.
In a written statement Clark Ouzts, a spokesperson for Sygenta, the manufacturer of pinoxaden, says the company has not studied the potential effects of climate change on the herbicide's activity, but that “field research and commercial applications have not shown temperature to have a significant impact on the activity of Pinoxaden.”
Charla Lord, a spokesperson for Bayer, wrote in a statement that the company's herbicides are “extensively tested to meet all regulators' requirements” and “labeled so applicators know how to apply for them for optimal control and success.” The company did not respond to specific questions regarding the efficacy of their products under high temperatures, although the company has posted about the challenges of high-temperature spraying on its website.
Corteva, which makes herbicides incorporating 2,4-D, did not respond to requests for comment on how high temperatures affect the herbicide's performance.
Not everyone is convinced that these experimental findings spell trouble for farmers. Some researchers and weed experts say that laboratory conditions differ radically from the field, making the results less pertinent. “I don't think we could say for sure that this is having an impact at the real-world scale,” wrote Brad Hanson, a weed expert at the University of California, Davis, in an email to Undark. Hanson worked with Matzrafi on the research published last year.
Hanson, who works with California farmers as a researcher and extension specialist, also wrote that farmers typically use enough herbicide to overcome any small changes in weed sensitivity brought on by heat.
Kassim Al-Khatib, a crop physiologist at the University of California, Davis who has investigated how herbicides perform under heat and humidity, wrote in an email to Undark that the studies are carried out under carefully controlled laboratory conditions that farmers would never find in their fields.
“What happens under controlled conditions does not generally support what happens in field conditions,” he wrote.
It's not clear whether herbicide manufacturers are prepared for the coming challenges of a warming planet.
In his own research, Al-Khatib has studied the effect of temperature and humidity on a small number of herbicide types and weed species. In the cases he has studied, he says, herbicide efficacy generally improves at higher temperature and humidity, unless temperatures exceed 100 degrees Fahrenheit.
Matzrafi and Jugulam agree that the lab does not reflect the more complex farm environment.
“But I don't think it lessens the importance of the results,” Matzrafi wrote. He, Stahlman, and others say they have seen the effect in the field for themselves.
“I think we are seeing something. Over the next 10 years I think we will see more. It's going to be a major problem,” says Chuck Otte, a K-State Research and Extension agent in Geary County, Kansas, who primarily works with farmers.
The research findings are trying news for farmers who rely on herbicides to keep increasingly weaponized weeds at bay. For now, some farmers are striving to stave off some of the effects from heat by spraying herbicides during cooler periods of the day. In the heart of summer, Carie Moore says she sometimes wakes before dawn to spray her 650-acre farm in North Dakota before the heat climbs too high, occasionally topping 100 degrees Fahrenheit. But as the globe warms, farmers will face narrower windows during which temperatures are cool enough to spray, says Ziska. And Matzrafi's research suggests that spraying during cooler periods doesn't guarantee that herbicide efficacy isn't affected by bursts of heat that come later in the day or even the following day.
And sometimes farmers can't avoid spraying herbicides in the heat, particularly on huge farms with several thousand acres.
Otte says that skeptics might not realize their herbicides are not working because heat has given weeds a helping hand. They might first assume that an array of other common factors are at fault, such as herbicide resistance, lack of rainfall, or too little herbicide. “There are so many confounding factors it is difficult to sort it all out,” he says.
In the long-run, farmers will need to lessen their reliance on herbicides and instead use other techniques more often used in organic farming today to keep weeds at bay, many experts say. For example, planting cover crops such as spring oats or crimson clover helps stop weeds taking root in bare soil and growing a variety of crops in rotation can wrong-foot weeds helping to suppress populations. Moore is already moving in this direction. She rotates soybeans with wheat, barley, and a couple of other crops and plants a variety of additional cover crops including rye and peas.
She also occasionally tills the soil to help stifle weed growth. “The less we have to spray chemicals the better,” she says.
Yet, to keep up yields, farming can't entirely abandon herbicides, says Ziska. With very few new chemicals on offer, farmers will need to be more careful with the herbicides they have now to ensure they continue to work in the future. Manufacturers need to provide farmers with better advice on when and how to use herbicides, adds Matzrafi.
“Farmers can no longer just spray and pray,” says Otte.
Natasha Gilbert is a freelance reporter in Washington, D.C., who has spent over a decade covering the environment, agriculture, and sustainability.
Original source: Undark • Dec. 7, 2020/h5>/h5>/h3>/h2>
- Author: Ben Faber
"A Virtual Conference to Discuss Real-World Weeds".
That's a great tag-line for the California Weed Science Society conference and a sign of the times.
Even though our in-person interactions as weed researchers, managers, and regulators has been put on hold this year, weed control goes on and so does the need for the education and updates provided by the CWSS.
Please remember to register for the conference this year to keep up your education and training and get the latest information as well as supporting YOUR California Weed Science Society. The program committee has put together another high-quality program that touches on the many aspects of weed science in California.
Here's the link to the registration page:
While there is a lot of value in our normal in-person 2.5 day conference format, there are a few benefits of the online format.
- You can view the sessions at your convenience since they are prerecorded. In a state like California, there's no "off-season" for everyone and in this format you don't have to dedicate 3 days to get this great content.
- We have several registration options if you don't want to participate in the whole event. Of course it's a better deal (per credit) if you register for the full program, but there are several options if you just want the Laws and Regs, or just the breakout sessions, etc.
- No travel expense! If you've been CWSS-curious but have not been able to justify the time or expense of the travel in the past, this is your opportunity!
- Lastly, this may be a one-time opportunity to see weed science experts from around California and the US delivering cutting-edge research updates while wearing sweatpants and broadcasting from the spare bedroom in their house while their dog barks at the mailman - what an opportunity! (just kidding, we actually have high quality professional video and audio and on-demand retrieval of the presentations).
The content will be available online from January 25 through February 26. Register early before the price goes up!
Here's how to get to the registration page:
Here's the current program agenda:/span>