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“Usually, farmers will get up early in the morning to go out and spray their fields as soon as they can see enough. But, what we really ought to do is wait until about two hours after sunrise,” remarks Tom Wolf of Agrimetrix Research and Training.

Wolf recommends spraying after the air temperature has risen two degrees Celsius above the temperature at sunrise, the coldest time of the night.

“By then, the sun has warmed up the soil, the air has warmed up a little bit, and we start to get a little bit of breeze so there is more turbulent mixing,” he explains.

Many producers want to spray in calm conditions to avoid off-target movement, but calm conditions can also be associated with inversions, which are unfavorable for spraying.

“An inversion is defined by a temperature difference between two heights,” he explains, describing how there can be different temperature layers in the air.

Rising air

In sunny conditions, the sun heats up the soil, and the ground becomes warmer than the air above it.

“The higher up we go from the ground, the more the air cools. That’s a normal daytime condition – air near the ground is warmer than the air above it,” Wolf says.

Even without the presence of the sun, air is typically cooler higher up, as illustrated by snowy mountaintops.

“There is less air pressure there. The rate of cooling with elevation is related to air pressure, and it’s called the adiabatic lapse rate. It means, if we take a parcel or air and simply elevate it, it will expand a little bit because there is less air pressure the higher we go,” he comments.

“That expansion takes work. The molecules have to physically move further apart and that work is temperature related,” he adds.

Typically, the rate of cooling is approximately one degree Celsius per 100 meters.

Warm soils

“When it’s sunny out, that rate of cooling is actually much faster because the soil has warmed the air near the ground, and as that dissipates, it causes the air to cool faster,” Wolf describes.

A parcel of air that is elevated from the ground on a sunny day, despite cooling as it rises, will still be warmer than the air around it, and therefore, it will continue to rise.

“Once that parcel of air rises, it’s gone,” he states. “Likewise, if we displace a parcel of air from above and move it down, the opposite happens.”

A cold parcel of air that sinks is still colder than the air around it when it nears the warm soil, so it is pushed all the way to the ground.

“What we have is very high turbulence – lots of parcels rising and falling. That’s called turbulent conditions, and it leads to dispersion of spray,” he explains.

Spray clouds

A spray cloud released into turbulent air moves across the currents and disperses out over the field until it’s gone.

“If I was to release a spray cloud a few meters to my right, by the time it was a few meters to my left, it would probably be about five meters high. It would just go up, and by the time it reaches a little bit further downwind, there’s almost nothing left of it. It’s gone into the atmosphere. That’s why spraying under sunny daytime conditions is favored,” Wolf says.

On a day without sun, the ground can be much cooler than the air above it.

“If we take that same parcel of air and make it rise, it will warm a little bit as it rises, but it will still be colder than the air around it. As a result of that, it will fall back down to the ground and fall to exactly the same place where it came from,” he continues.

A parcel of air from above that is displaced downward will likewise return to where it started. Therefore, no mixing takes place in the air, creating two distinct layers.


“The parcels of air cannot be displaced,” states Wolf. “We see this in the evening fog sometimes, for example when the fog is hanging just at windshield height,” describes Wolf.

These distinct temperature layers are known as an inversion, and inversions are most common early in the morning and throughout the night.

“The reason it’s dangerous to spray in an inversion is because if the spray cloud doesn’t mix up, it will stay very concentrated, and it will cause a great deal of damage where it sits,” he remarks.

Large spray particles fall to the ground, but smaller particles remain buoyant in the air and can be carried for miles without dispersing.

“The small particles rely on atmospheric turbulence to disperse themselves. That’s what the sun will do for us,” he notes.

Before spraying, Wolf recommends, “We should take the temperature at sunrise and wait until we get about one or two degrees Celsius above that. Then, we’ll know the sun has done its work.”

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..

Goshen County – A group of natural resource professionals gathered in northern Goshen County on July 16 to tour and investigate pasture die-off that occurred this spring.
    The group gathered first on the ranch of Doug DesEnfants near Prairie Center.  A few pastures in the area failed to green-up or show any signs of growth this spring and the DesEnfants contacted Dallas Mount, with the University of Wyoming Cooperative Extension Service. “I was completely baffled by it.  I knew I needed to get a group together to assess this situation and make recommendations to Doug as well as address the ecological concerns this will create.  The affected pastures seemed to be irrespective of ownership or management, this was something environmental causing the damage,” said Mount.
    The group included employees of the Natural Resources Conservation Service, the Southeast Wyoming Resource Conservation and Development Council, conservation districts and the University of Wyoming Cooperative Extension Services as well as interested neighbors that had similar conditions in their pastures.
    “We talked about drought, funguses, herbicide even considered aliens,” laughed Mount. “The most likely explanation seems to be army cutworms that caused the damage by feeding on the rangeland plants either last fall, or early spring.  The cutworms work at night, or even underground and can do their damage completely unnoticed until the plants show signs of stress.”
    UW Extension Entomologist Scott Shell took soil samples back to Laramie for testing to see if he could find pupal casings that would likely be left behind by the cutworms when they turn into the familiar miller moths that pester homes in the spring.
Mike Smith, UW Extension Rangeland Specialist said that during his 30-year career this is the first time he has seen anything like this.  “Likely you all will never see it again,” said Smith to the affected ranchers. Shell explained that once the cutworms affect an area that area is unattractive to them in the near future because they feed on the healthy plants.  
The main question for the landowners now is do they reseed the affected areas or just defer grazing to allow the perennial grasses to repopulate the area naturally.  Some ranchers seemed to think the reseeding would be necessary to speed recovery of the land, while others thought simply deferring grazing would be enough.  The Goshen County conservation districts will be made aware of the situation and NRCS expressed an interest in using some EQIP funding to assist the ranchers in either reseeding and/or grazing deferment to help the areas recover.
    “If ever there was a need for conservation dollars to be put to work, this is an ideal situation,” said Mount.
    For questions concerning the army cutworm damage contact UW Extension Educator Dallas Mount at 307-322-3667 or This email address is being protected from spambots. You need JavaScript enabled to view it..

Cody – Landowners from around the Cody area gathered on April 4 for a workshop by University of Wyoming Sheridan Research and Extension Center Director Brian Mealor on cheatgrass management, funding and local prevalence.

“For a long time, we thought there was an upper elevation limit, but within the last 10 years, we’ve seen upward expansions and movement into areas cheatgrass hadn’t previously occurred,” said Mealor.


Cheatgrass is primarily a winter annual plant, meaning that its top priority is seed production, said Mealor.

“It doesn’t invest a lot of resources into structure development, but it can get a lot of fibrous roots. It’s really good at taking up moisture from snowmelt,” he explained.

Mealor noted that moisture has a large impact on when cheatgrass will germinate.

“If we get fall moisture, most of the cheatgrass in this area will germinate in the fall,” said Mealor.

According to Mealor, if cheatgrass overwinters, or vernalizes as a seedling, the plant will produce more seeds than if it vernalizes as a seed.

The cold period is critical to cheatgrass reproduction, he commented, explaining, “If it doesn’t vernalize, it doesn’t go through to seed.”

Cheatgrass density also influences seed production of individual plants.

“When it’s really thick, each plant produces fewer seeds per plant, but if we thin it out, they produce more seed per plant, so we end up with pretty consistent seed production,” he continued.


While many landowners think that native perennial biomass declines because of an increase in cheatgrass, Mealor explained that the increase in cheatgrass can be because of increased bare ground, as well.

“It’s a chicken and egg thing. We do know that cheatgrass is highly competitive for moisture in the early spring, which is part of why it becomes such a problem,” he said.

Cheatgrass presence is also able to change landscapes, particularly when looking at the example of changing fire intervals.

“Fire doesn’t always equal cheatgrass, but a high amount of cheatgrass does increase the risk of a fire,” commented Mealor.

He continued, “If we look at traditional historical fire intervals, it is safe to assume we see fires every 40 to 50 years. There are places along the Snake River that burn every three to five years.”

The prolific seed production of cheatgrass is another factor that makes it highly competitive with native species, producing 400 pounds of seed per acre.

“It stays viable in the ground from five to seven years,” commented Mealor. “If we’ve only got 10 percent carry over, that’s still a lot of seed.”


While many treatments exist and the plant itself is not difficult to kill, Mealor stressed, “One treatment is not enough because of seed viability. Biology informs management. There is no silver bullet. It’s a long-term sort of commitment.”

Chemical control is one of the most common and effective methods for both short-term and long-term control.

The most common chemical used is Imazapic, also know as Plateau, which does not having any grazing limitations after application.

Imazapic may also be mixed with glyphosphate, but landowners should be aware that the chemicals will not be selective.

Other chemicals including Matrix, which is available as the off-brand. Laramie, Canter R+P, Landmark EP and Outrider are also available but have differing requirements than Plateau for application rate and grazing.

“It’s open to interpretation, but the way I read the Matrix label, there can be no grazing for one year after application,” he continued.

Mealor noted that a new herbicide called Esplinon that is currently in trials.

“It’s a root growth inhibitor. It doesn’t affect established grasses at all,” he said.

Grazing is another common method that landowners use when managing cheatgrass.

“In some cases it works, but 'work' is relative. The results are a little more subtle,” continued Mealor.

However, grazing can be particularly effective when used in combination with other control methods.

“When we don’t graze, we get a buildup of litter. Cheatgrass emergence and establishment is facilitated by a litter layer,” he said.

A large amount of research is currently being done on utilizing various bacterial and fungal strains as biological control methods, but many concerns about practicality must be addressed.

“At this point, I don’t think we have an adequate biological control method,” noted Mealor.


Several factors should be considered when deciding whether to treat a particular site.

“Timing is important. If the plants gets too big, our treatment is just not going to be effective in killing the cheatgrass,” said Mealor.

Landowners should also consider how much natural recovery potential there is at a site.

“Is there some natural recovery potential on the site? We can get the herbicide to do exactly what we want it to, but there’s just bare ground,” he commented. “Then we’re talking about a restoration project and not a weed control project.”

Mealor continued, “I firmly believe that the best long-term suppression comes from a healthy perennial plant community. If it comes to the point that we need to reseed, we’re not going to have long-term suppression.”

Mealor outlined three key considerations when making decisions at landscape level.

“One, leverage is important. Next, every tool has its limitations and finally, there are some unintended consequences of doing a good thing that we should be prepared for,” said Mealor.

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

Cheyenne— The devastating impacts of the bark beetle was a primary discussion topic during the House Ag Committee Hearing in early May.
Representative Cynthia Lummis explained the bark beetle has taken a toll on about 17 million acres of forest in regions one, two and four within the state.
“The magnitude of the problem is really difficult to grasp without seeing it. Forest health is critical to Wyoming’s health and economy, and so is the health of Wyoming’s vast ranges and open spaces; particularly watershed. In our semi-arid state the health of the land is synonymous with the health of state,” commented Lummis.
State Forester Bill Crapser explained that Wyoming has approximately 11.5 million acres of forest. Of those acres about nine million are in federal ownership and about 2.5 million are in private, tribal or state ownership.
“Wyoming forests are facing health issues that are probably unprecedented. We’ve never seen anything like what we’re seeing with the bark beetle across the state,” adds Crapser.
“In the last couple years this beetle has exploded. There are 3.6 million acres of dead forest in the Medicine Bow Forest and National Forest in Colorado. That’s an area the size of Connecticut,” adds Regional Forester for the Rocky Mountain Region of the U.S. Forest Service Rick Cables.
In addition to dying trees, Cable says another emerging issue is falling trees.
“On average we’re going to see 100,000 trees fall per day for 10 years over this 3.6 million acres unless we have a wind event that causes them to fall early,” says Cable.
Falling trees threaten infrastructure and require an increased labor force to keep trails open and remove trees from recreational sites.
“We’ve got over 550 miles of power lines within this area. One tree on a power line and you’re out of power. So you can imagine, as you look at those corridors, how much cutting back adjacent to the infrastructure we need to do to protect the power source. Another 211,000 acres adjacent to communities need to be treated to protect them from fire.
“The threat of wildfire, both in the urban interface and outside the interface, is on the great increase. The occurrence of fire and the number of acres burned has almost quadrupled over the last 10 years,” notes Crapser.
“There are 3,700 miles of road in this part of the country. We’ve treated about 500 miles, which leaves 3,200 miles to go. It’s becoming very labor intensive to keep trails open and we’ve had to remove every tree surrounding some recreational sites,” adds Cable.
Crapser includes the lack of a viable forest products industry as another growing concern. Noting that seven years ago there were seven large or fairly large sawmills in the state and today there is one in operation.
But of all the issues, both men list the impacts on watershed at the top.
“This area contains the Colorado River Basin, the Rio Grande River Basin, Arkansas River and Platte River. There are 177 counties that depend on water from this watershed and 13 downstream states in addition to a large agriculture interest. The condition of this watershed isn’t very good right now due to the mortality of the trees and the falling trees,” comments Cable.
“There’s an old saying in Wyoming that whiskey is for drinking and water is for fighting. That gives you an indication of how important water is to our farmers and ranchers,” adds Lummis.
“Water quality and quantity are important issues both in our state and this part of the country. Habitat is under pressure and we’re seeing more and more fragmented land ownership, which also has an impact. A lot of ranchers and farmers can’t afford to stay in the business anymore for various reasons and they are dividing up their lands. Our ability to manage those fragmented lands is becoming more and more complicated that continues to be an issue,” adds Crapser.
A key element of the 2008 Farm Bill was a state directive to develop a statewide forest resource assessment and strategies to address any issues raised in the assessment. Crapser says that Wyoming has already completed the task and to the best of his understand is the first state to do so.
“I’m proud of my crew for that. We took an all-lands approach to forestry in the assessment and achieved special analysis using 14 key data layers that were identified by agencies, special interest groups and individuals. These include everything from development risk, wildfire risk, insects, disease and aquatic habitat, to green infrastructure.
“What we hope to do with these documents is help focus our efforts and help focus the Forest Services’ efforts and develop projects that will deliver maximum return on our investment. We believe the partnership between the state and federal agencies and the forestry service aspects of the Farm Bill will all contribute to this success,” says Crapser.
Cables notes that last year Secretary Vilsack delegated or dedicated over 40 million to be spent on the forest health issue, which everyone really appreciated.
“It’s a daunting challenge. There is a lot of work to be done, but there are a lot of opportunities as well in terms of jobs, sustaining supplies of wood and biomass and the research associated with it,” he explains.
Heather Hamilton 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.

Lingle – The final year of the Cheatgrass Restoration Challenge at the University of Wyoming (UW) James C. Hageman Sustainable Agriculture Research and Extension Center (SAREC) revealed a lot of diversity in the 13 plots in the contest.

“The Cheatgrass Restoration Challenge started in Lingle three years ago,” according to Brian Mealor, UW Sheridan Research and Extension Center Director, who oversaw the project. “It is a contest that was about taking a widespread and very important resource concern, which is the invasion of cheatgrass and its impacts across the western U.S., to see how others would approach it.”

Mealor explains, “Instead of a research team implementing treatments and collecting data through time, we appreciate there is a lot of local, expert knowledge around from people who know how to control weeds.”

“We had people from producers and students to government agencies who actively addressed these concerns and came to the center to compete in this competition,” he says.


After three years and a number of treatment methods, Mealor announced the winner of the contest during the SAREC Open House in late August.

Larry Cundall of Cundall Ranch in Glendo, Sydney Bureks and the Natural Resources Conservation Service (NRCS) partnered to come out on top of the 13 teams competing in the diverse competition.

While accepting a belt buckle, Cundall told producers that this competition was an opportunity for ranchers to work with NRCS and share ideas.

“It is the way it should be,” he said. “We were able to bounce a lot of ideas back and forth to improve the vegetation on our plot.”

After touring the plots during the open house, producers were able to vote on the “People’s Choice winner,” which was the SAREC team composed of Brian Lee, Kevin Madden and Troy Cecil.

Their treatment method consisted of spraying, mowing and reseeding the plot to wheatgrass. During the tour, producers noticed a nice stand of wheatgrass had overtaken the plot, helping them gain the win.

Learning from the contest

Mealor told producers he learned a lot from this contest, and the best part has been analyzing the data and doing evaluations.

“One of the reasons I wanted this contest was because I was tired of people asking me how to get rid of cheatgrass and not knowing the best answer,” he told producers. “I wanted to see how other people would approach it. This contest has drawn interest from a lot of producers who are concerned with cheatgrass and what they can do to eliminate it.”

Contest origins

The contest was approved for a three-year run starting in the spring of 2015. Everyone in the contest had to agree to a set of criteria that would be used to judge each team’s performance, including how much cheatgrass they eliminated, how much forage productivity was improved, diversity of desirable species on the site and scalability.

“We also wanted to know how scalable the practices were if they were implemented across a larger area,” Mealor explained.

Other criteria were economical treatments, which included the benefits and costs of each of the different practices, and an educational program.

“The challenge was to take a piece of ground that was almost entirely cheatgrass and restore it with perennial cover for diversity, using economically sound and appropriate practices,” one contestant says in a video about the contest.

“Cheatgrass is something of interest to every producer and agency,” another added.

It also served as a unique opportunity for students to take what they learned in rangeland studies and other agriculture classes and apply it to a real-life scenario.

The contest also educated even the most seasoned professionals.

“We can look at these plots for education of what did and didn’t work and what people can try,” Mealor says. “We had everyone from current undergrads at UW, whose team was a rotation of students, to seasoned professionals who had been at it for a long time.”

“Everyone’s practices were diversified – from a very minimalist approach that engaged only a few practices they thought would move the ball forward to some teams who were very active in the number of practices they did,” he says.

During the contest, plots were disked, burned, sprayed, mowed and grazed with cattle and goats in attempt to reduce the cheatgrass populations.

Gayle Smith is a correspondent for the Wyoming Livestock Roundup. Send comments to This email address is being protected from spambots. You need JavaScript enabled to view it..