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Noxious Weeds

With a unanimous vote on Feb. 11, the Board of Agriculture passed a resolution to add black henbane to the state’s list of designated noxious weeds.

“At the public hearing, there were folks who commented in support of the resolution, but there were no comments opposed to it,” comments Slade Franklin, weed and pest coordinator with the Wyoming Department of Agriculture.

The board took action on the resolution in a business meeting immediately following the public hearing.

“It was a straightforward hearing, and there wasn’t anything too concerning,” he notes.

Black henbane has already been listed in numerous Wyoming counties as a noxious weed.

“Concern had grown to almost all 23 counties in the state. It was getting to the point where we needed to start addressing it from a state level,” Franklin says.

The weed is especially prevalent along pipelines and in riparian areas.

“Black henbane likes disturbed lands,” he explains. “Especially in the southern part of the state where vegetation is scarce, more weeds in general are likely to come in after a disturbance such as when a new pipeline is put in.”

In Teton County, the weed is often a problem around new home construction.

“It is diverse in terms of areas that it can attack,” Franklin notes.

When the plant reaches maturity, a thickened lid pops off of the urn-shaped fruit, spilling black seeds. A single plant can produce up to half a million seeds.

“I’ve had reports on black henbane from areas all over the state,” states Franklin.

Last year, the Board of Agriculture wrote a letter to the Weed and Pest Council, asking them to consider adding black henbane to the state’s designated weed list.

“The rules and regulations state that a resolution must start with a weed and pest district request to the council, who then moves it forward to the Board of Ag for consideration,” he says.

After the board’s request, three different weed and pest districts moved forward with a resolution.

“We moved one of the resolutions forward,” Franklin states. “It is the 26th weed on our designated list.”

Black henbane is an annual or biennial plant that grows up to three feet tall, and the entire plant is covered with greasy hairs. Leaves are up to eight inches long and six inches wide, shallowly lobed and heavily scented.

“It is a poisonous plant, so there are also concerns from an agricultural perspective about its toxicity,” adds Franklin.

Generally, livestock will avoid the weed unless it is the only available forage.

“There is potential for concern in targeted grazing or with livestock that is not used to it,” he adds.

In controlled dosages, alkaloids from black henbane are used in medications but the plant is also poisonous to humans.

“Black henbane is treatable,” Franklin continues, noting that there are several herbicide options for control of the plant.

Escort and Tordon are examples of herbicides that work effectively for controlling the weed.

“It’s not a matter of ‘can we treat this,’ it is a matter of ‘do we need to treat this,’ and that is why it has made it on the list,” Franklin explains.

Other common names for black henbane include insane root, stinking nightshade, fetid nightshade and hog’s beam.

Natasha Wheeler is editor of the Wyoming Livestock Roundup and can be contacted at This email address is being protected from spambots. You need JavaScript enabled to view it..

Torrington – “There’s a lot of demand to figuring out how to best and most effectively manage cheatgrass in Wyoming,” states University of Wyoming’s (UW) Extension Weed Specialist Brian Mealor. 

“Last fall, we had good moisture levels. That’s one of the reasons why cheatgrass is so abundant and doing so well this year,” explains Mealor. 

He adds, “Cheatgrass is really easy to kill. It’s an annual. Pull it up and it’s dead, but it’s really hard to get rid of.” 


Cheatgrass is a winter annual grass but has the flexibility to have multiple germinations in the fall, spring and summer. Typically cheatgrass germinates in the fall and overwinters as a seedling, where it is able to kick-start its growth and mature before any other perennial grasses.  

The hearty plant is able to withstand cold temperatures and will turn purple when it is about to dry up and go dormant. 

“Almost all of our native plants are completely shutdown at freezing, but cheatgrass is able to elongate its roots and germinate a little above 32 degrees Fahrenheit,” notes Mealor. “That’s one of the reasons it’s problematic.” 

“Cheatgrass at a high density is highly competitive. Seed production is the only way cheatgrass grows from year to year,” states Mealor. “It has been documented cheatgrass can produce up to 500 pounds of seed per acre.”  

Ecosystem transformer

Cheatgrass is considered an ecosystem transformer because it changes the way ecosystems work. The invasive grass suppresses the growth of native species and perennial grasses when it grows at high densities, leading to a loss of biological differences of plants.

Cheatgrass can also become an extreme fire hazard when it dries out. 

“A high production of cheatgrass can burn very hot, and this is one of the reasons we’re seeing increased fire frequency and increased fire intensity across the western U.S.,” comments Mealor. 

He continues, “This gives us another level of challenge dealing with cheatgrass, especially when we are trying to maintain sagebrush ecosystems for wildlife habitat.” 


Fire can be used as a method to control cheatgrass, but it is most effective when the seeds are in the air instead of on or in the ground. 

“Fire typically doesn’t reach a high enough temperature to kill seeds when they are already in the ground,” comments Mealor. “Most reports indicate around 90 percent of cheatgrass seeds germinate within one year and viability of those seeds can be up to eight to 11 years.” 

By preventing seed production of cheatgrass for three years, the soil seed bank might be depleted and keep cheatgrass from becoming established, notes Mealor. 

However, cheatgrass thrives when there is free nitrogen in the soil and is often times made worse after a field has been burned. 


“Prevention is really our highest leverage strategy against cheatgrass because if there is no cheatgrass onsite, we don’t have to worry about control,” states Mealor. “For very small populations of cheatgrass, producers might want to think about eradicating the population.” 

Mealor notes unsuccessful long-term management of cheatgrass could unfortunately lead producers to considering abandoning their property.  

“Herbicide has been the most consistent positive result we’ve seen for cheatgrass control,” he says. “However, we recommend to start an assessment of the cheatgrass invasion to know what the recovery potential is for the ground, then go from there.”


“When doing any type of reseeding, don’t pull the plug until after three years because sometimes it takes that long, especially for native species, to come up and be established,” claims Mealor. 

Crested wheat grass, western wild rye and pubescent wheatgrasses compete very well with cheatgrass, but the societal push is away from introduced species towards native species, mentions Mealor. 

Mealor spoke at the cheatgrass workshop held in Torrington on June 11. The workshop included discussions of cheatgrass management practices and a tour of the UW Sustainable Agriculture Research and Extension Center (SAREC) to look at the test plots of cheatgrass. 

Madeline Robinson is editor of the Wyoming Livestock Roundup and can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it..


While the herbicide Plateau has been noted as the most effective way to kill cheatgrass, promising new bio-control research of using a Pseudomonas bacterium to target cheatgrass roots is being conducted in Converse and Goshen counties. 

Converse County Weed and Pest District Supervisor Cheryl Schwartzkopf conducted tests using the cheatgrass bacteria in October 2013.  

“We apply the cheatgrass bacteria during October to November,” says Schwartzkopf. “For this bacteria to work, there needs to be some moisture to help incorporate it into the ground and for it to take effect against the roots of cheatgrass.” 

Sunlight kills the bacteria, and it must remain frozen until it is mixed with water or a mixture of water and herbicide when it is applied to infested cheatgrass fields. Ten grams of the concentrated bacteria is needed for every five acres. 

“Bio-control is a very slow process. It takes about three years to completely take affect against the cheatgrass,” she says.

She adds there has been a decrease in the amount of cheatgrass on her test fields, but more time is needed to see the full effect the bacteria can have on cheatgrass. 

The cheatgrass bacteria are already present in Wyoming’s soils but are not concentrated enough to have an effect on and kill cheatgrass. 

Schwartzkopf notes the bacteria remains in the location where it is applied and will not migrate. The bacteria will not suppress any crops or native plants and can only take effect on cheatgrass after it has germinated. It also can have an effect on jointed goat grass and medusahead. 

“The lifespan of the bacteria is dependent on the amount of cheatgrass. If there aren’t any cheatgrass roots for it to feed on, it will reduce back to the natural carrying capacity for that site,” comments Schwartzkopf.


Poisonous plants disrupt management on millions of acres in the United States. Larkspurs (Delphinium spp.) kill more cattle on high mountain rangelands in the western U.S. than any other plant or disease.  These plants dominate the tall forb community and kill cattle when consumed at a sufficient dose.  Cattle losses from poisonous plants represent the value of the animals and prior inputs into each animal. Chemical control of tall larkspur can reduce death losses incurred while grazing infested rangelands.

There are added benefits to controlling tall larkspurs.  It can increase forage productivity of the pasture and increase the flexibility of management.  Managers usually delay grazing until after larkspur plants have senesced, or dried up, and are no longer toxic to cattle.  At this point, pastures often have less nutritious forage.  Control of larkspurs would allow for use of these pastures earlier in the growing season.  Controlling larkspurs can reduce other indirect losses.  These losses can include overutilization of other pastures, cost of leasing larkspur-free pastures, fencing, feed supplements, herding, monitoring, cholinergic drugs and labor.

Recently an herbicide efficacy study was performed in the Big Horn Mountains of Wyoming.  This study used a new herbicide called aminocyclopyrachlor. Aminocyclopyrachlor (AMCP) is a new synthetic auxin herbicide that works as a growth regulator.  It has good residual characteristics that give it the ability to control perennial broadleaf weeds.  However, it may reduce grass production from both direct damage to plants and by potentially reducing subsequent seed production.  Dupont will be marketing AMCP for use in rangelands and pastures in a variety of herbicides including Streamline (AMCP + metsulfuron-methyl) and Perspective (AMCP + chlorsulfuron) in the future.  Perspective and Streamline were used in this research due to their likely labeling for rangeland and pasture use and were thought to likely have a significant impact on tall larkspur 

Simply stated, research results indicated that application of Streamline and Perspective (and also Tordon 22k and Escort XP) could control tall larkspur to a level that would provide a significant reduction in cattle deaths. However, application of these herbicides should be weighed against decreases in diversity and vegetation cover as well as shifts of plant species composition.  The next step was to evaluate the economics of using these herbicides.  

To do this, we compared spraying the recommended rates of picloram (Tordon 22K) and metsulfuron-methyl (Escort XP) and the rates of AMCP-containing herbicides resulting in 90 percent control in the previous study.  The cost of applying each of these chemicals was compared to leasing similar, larkspur-free pastures, as seen in Table One, pasture and to accepting either a 2.5 or five percent death loss.  This study assumed that death loss would be reduced by 90 percent with chemical control.  It also assumed that cost of herbicide application per acre would be  $9.50 for aerial application, $24 for boom application and $37.50 for spot application.  Herbicides would only be applied once.

The economic analysis found that, in this situation, it is always more profitable to lease non-infested pasture instead of accepting either amount of death loss.  Chemical control would require two to six years of control for Perspective and two to five years for Streamline to break even compared to leasing similar larkspur-free pasture.  Tordon 22K would require five to eight years of control and applying Escort XP would require three to five years to break even.  When chemical application is compared to accepting either amount of death loss, the break-even time is a maximum of three years for any of the herbicides used.  

Our results indicate that, if three years of control are obtained from one herbicide application, the cost of applying herbicides are justified as compared to accepting either a 2.5 percent or five percent death loss to larkspur, as seen in Table Two. Application method (aerial, boom spray or spot spray with backpacks) should also be taken into consideration because of their effects on cost.

The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by UW Extension is implied. 

Brandon J. Greet is a UW Assistant Extension educator in Worland and can be reached at 307-347-3431 or This email address is being protected from spambots. You need JavaScript enabled to view it.. Brian A. Mealor is an assistant professor and Extension weed specialist in Laramie and Andrew R. Kniss is an assistant professor in Laramie.

“I think it’s important for people to be aware that glyphosate resistance has been confirmed so that we can take proper management action before it gets worse,” notes University of Wyoming Extension Educator Caitlin Youngquist.

Recently, a kochia plant was confirmed to have resistance to glyphosate – the active ingredient in Roundup and other herbicides.

“It was brought to my attention through Extension. I was able to coordinate with growers, the local Weed and Pest, the University of Wyoming (UW) research station and a weed specialist in Laramie,” Younquist explains.

A rapid-response bulletin was released, warning growers, homeowners and landowners to be on the lookout for additional cases. The announcement also included suggestions for herbicide alternatives, based on the crop or land being managed.

Weed management

“Herbicide stewardship is very important for preventing further spread of herbicide resistance,” Youngquist says.

If a herbicide-resistant weed is suspected, it should be destroyed, according to Gustavo Sbatella, assistant professor of irrigated crop and weed management at the Powell Research and Extension Center.

“Do not let it go to flower or seed,” Sbatella states.

The next step is to plan for herbicide rotation, changing the mode of action for controlling kochia weeds.

As an example, Sbatella explains, “If a farmer planted glyphosate-resistant sugarbeets and followed that with glyphosate-resistant corn, there is a possibility that the only herbicide that has been used in a two-year period is glyphosate. That puts a lot of selection pressure on any weed species, especially kochia.”

If those weeds begin to develop resistance, they may not be eliminated after herbicide treatments.

Identifying resistance

“If we have sprayed an area for any weed, and we notice that most of the plants where we have sprayed are dead or dying, but a few individuals are still thriving, that is a good indicator that we might have resistance there,” Youngquist notes.

“In the early stages of resistance, when we walk in the field, we are going to find some plants that are dying and some plants that are not. We will have different degrees after we spray in terms of plants that will die or survive,” comment Sbatella.

After other factors have been eliminated, such as spots that may have been skipped during herbicide application or tools that are not properly calibrated for even and accurate treatment, surviving plants may be an early indicator that alternate control methods are necessary.

“It’s important to be careful with the edges of our spray pattern,” Youngquist advises.

  Weeds along the perimeter of herbicide treatment may come into contact with the herbicide but not with a strong enough dose to be eliminated.

“Watch those areas where resistance can develop,” Youngquist suggests.

These areas also include ditches, roadsides, rights-of-way and other areas that have been repeatedly sprayed with the same herbicide, such as glyphosate.


“Kochia is an annual weed, and it is very common in much of the western U.S., including Wyoming,” Sbatella adds.

Kochia seeds spread very efficiently, and the plants are drought resistant and easily adapt to alkaline soils.

“It is one of the many tumbleweeds that we have here in Wyoming. It is probably one of the most common, along with Russian thistle,” he continues.

It is also one of the first weeds of the season to germinate. This time of year, the plants typically flower and produce large quantities of yellow pollen.

“They don’t have any flashy flowers,” Sbatella explains. “They are similar to ragweed in terms of how inconspicuous they are.”

Originally, kochia plants were introduced to the United States as ornamental plants, and they established easily in the western landscape.

“Along with downy brome, it is probably one of the worst weeds in the western U.S.,” mentions Sbatella.


Sugarbeet farmers in particular struggle with kochia infestations in their fields.

“With sugarbeets, we don’t have many herbicides that will effectively control kochia. We also don’t have as many modes of action as we do with other crops,” Sbatella explains.

When glyphosate-tolerant crops were introduced, kochia control improved dramatically.

“But, if we keep repeating the same treatments, with time it might lead to the development of herbicide resistance. That is probably one of the things we are seeing here,” he adds.

If resistance is suspected, Extension or local Weed and Pest agents can be contacted for assistance.

“Contact the local Extension office,” suggests Youngquist. “If the plant is resistant, remove it by any means necessary, such as pulling them by hand, mowing or spraying with alternative herbicides.”

Weed management experts in Wyoming are taking action and looking for solutions to control kochia.

“There is more to do, and it will require working closely with growers, landowners and right-of-way managers, such as railroad, county and city staff, to carefully manage how we spray and how we use herbicides for kochia and other weeds,” Youngquist says.

Natasha Wheeler is editor of the Wyoming Livestock Roundup and can be contacted at This email address is being protected from spambots. You need JavaScript enabled to view it..

Riverton – It was a crowded room at the Armory in Riverton on Jan. 30 to hear Brandon Greet present the findings of  ahis larkspur control study at the Fremont County Farm and Ranch Days. Greet, a University of Wyoming Extension Educator in Washakie County, researched the affects of four different herbicides on larkspur for his graduate program.

“Larkspur is one of the greatest forages for cattle,” Greet said. “It is the most nutritious and has about 25 percent crude protein in it. It is great forage except that it kills them.”

Dangers of larkspur

“Cattle might accidentally get some larkspur and like the taste. Larkspur has alkaloids in it that are bitter. Cattle actually don’t like the taste of it, but they eat it and think ‘that tasted horrible but it is so good for me,’” explained Greet, “so they eat more of it and begin to selectively eat it.”

The description of Larkspur, Delphinium Glaucum, in a guide to Rocky Mountain wildflowers even mentions that the bluish purple flower is responsible for more cattle losses than any other poisonous plant in the region. 

When cattle overdose on larkspur it causes ataxia and collapse. If they eat enough they suffocate, as it causes respiratory paralysis. The guide continues to say larkspur reproduces from seed, grows from its root crown and one plant can live up to 75 years. 

“Some people are able to prevent cattle from eating larkspur by feeding mineral,” Greet said. “While this has been successful where larkspur is only present in patches, researchers have not been able to prove that minerals cause the larkspur to not effect the cattle when digested or that they do not want to eat it.”

Larkspur does well in drought as it has a large taproot system and is more competitive then other plant species. Greet’s study was completed in 2010 and 2011, and climatic conditions do affect the herbicides’ control. 

Eliminating larkspur

Greet used four herbicides in his two-year study: Streamline, Perspective, Tordon 22K and Escort XP. 

“Based on my research,” Greet explained, “I don’t think Tordon is the go-to herbicide because it only gave me 41 percent control the first year.  Escort gave me 100 percent control the first year. But the second year, they got about the same. Tordon may give you good control, but in both cases Escort will give you better control.”

In the first year of the study, Escort only injured nine percent of the grasses. Escort does lower the biomass slightly, but Greet is not sure that will happen every time. Tordon actually helped increase the biomass, but saw 15 percent grass injury. Part of this is that Tordon causes some yellowing, but the plants continue to grow fine.

“Personally, if I’m not exterminating things, I can handle some injury to plant forbes,” Greet said.  “You will reduce your species richness with the smaller annual forbes being hurt by the herbicide. The annuals should come back in the following year from the seed bank. The perennial grasses did not seem to be affected.”

Greet’s study was located between Kaycee and Ten Sleep where larkspur is the prevalent forage. In low water years, larkspur is taller than the grasses, and, as cattle are side feeders, they tend to graze it more.

Research shows that if larkspur is controlled, you can figure on having 10 years of larkspur free pasture. Even if the larkspur regrows the next year, it takes the long-lived perennial 10 years to become a mature plant. Greet said he would argue with that research, and thinks that it is more correct to count on five years of control as the leafy plant will be present just not blooming. Greet urged the audience to check with their weed and pest district as some cost share for larkspur control.

Grazing impacts

In early spring larkspur is the most bitter and the most toxic, but cattle seem to not want to graze it. In late summer after it blooms and begins to dry out, the plant is more palatable and cattle will graze it more readily. The alkaloids are stored in the roots in the winter and released into the plant and leaves in the summer.

If cattle consume 20 milligrams per kilogram of body weight, larkspur will cause ataxia and collapse. They need a little bit more than that to make it so that they cannot breathe. 

“We’ve found cattle on their backs in the bottom of a draw,” Greet said. “We expect they were eating larkspur, collapsed on the side of hill and rolled down. Larkspur can kill in a number of ways.”

Sheep will graze larkspur, though it takes quite a bit to kill them. There is not quite the same death loss with them as in cattle. Greet said that the wild horses that run in his area do not seem to help in the control of larkspur and also don’t seem to be affected by it.


Treatment myths abound for the overeating of larkspur, and include turpentine, bacon fat, whiskey, chewing tobacco and bleeding the animal from the tail vein. Greet said that when bleeding has been successful most often the animal hadn’t eaten that much larkspur. He has come across research that seems to support the chewing tobacco treatment, though.

“There is question on whether the currently available drugs, Physostigmine and Neostigmine, actually work for livestock,” Greet said. “The treated animals might not be severely affected by larkspur. In some cases treating the cattle like you would for bloat has been successful.”

Greet took one last question before closing his presentation: Is the delphinium that grows in my wife’s yard the same thing as larkspur? 

“Yes it is, so I wouldn’t let your cows graze in the yard,” replied Greet. 

The questioner responded, “I wouldn’t let that happen. I like to eat supper.”

Melissa Hemken is a correspondent for the Wyoming Livestock Roundup. Send comments on this article to This email address is being protected from spambots. You need JavaScript enabled to view it..