All posts by tcweed

2018 Mosquito Update


Every summer the Teton County Weed & Pest District dedicates highly trained staff to study the effectiveness of our mosquito treatments in the Teton County region. We treat mosquitoes to reduce potential human health risks, as well as to reduce the overall nuisance mosquito population. Surveillance of adult and larval mosquitoes supplies detailed information on where and how we need to focus our management efforts.

2018 Mosquito Results

  • 240 adult mosquito traps were set throughout the summer
      • 27 different species from 4 genera were collected
      • Mosquito numbers peaked during the last week of June and stayed high through the first two weeks of July

A Comparison of Adult Mosquitoes Caught by Week from 2016 – 2018

The week number is along the X-axis. The first Y-axis shows the number of mosquitoes caught, and the second Y-axis shows the number of traps set.  The circles show the number of traps set each week from 2016 – 2018, and the columns represent the total number of mosquitoes caught by year. Equal trapping effort has not been applied across weeks or years. Weeks with greater numbers of traps did not always yield higher numbers of mosquitoes. The graph suggests that mosquito populations were similar in 2016 and 2018, and that a greater number of mosquitoes were produced in 2018.

For reference, the 21st week in 2018 was the fourth week of May and the 37th was the 3rd week of September.

2018 Results, Continued

  • Over 5,000 larval sample points were collected.
      • A sample point is when a dipper is used to visually check a water sample for the presence or absence of mosquito larvae. TCWP collects samples of mosquito larvae from various habitat types throughout the summer and brings samples back to the TCWP lab to rear them into adults.
      • Reared 2,613 mosquito larvae into adults. This information allows us to build relationships between habitat and preferences of mosquito species.
  • We made eight adulticide runs throughout the 2018 summer (adulticide: use of fog trucks to combat large mosquito populations). 
      • Decisions to utilize adulticide are based on adult mosquito surveillance including the number of mosquitoes we collect, the species, and the neighborhood where we collect them.
  • Culex tarsalis is the mosquito species we are most concerned with in Teton County due to its competency as a vector for West Nile virus.
    • We target this species as much as possible for all our management efforts throughout the summer.
    • TCWP tested 61 mosquito pools for West Nile VirusAll tested mosquito pools were negative. All of the Culex tarsalis collected from the same trap on the same day were tested together.
    • In contrast to the general mosquito population, Culex tarsalis mosquito populations peak later in the summer.

Comparison of the number of collected adult Culex tarsalis mosquitoes across years by week number.

Our lab manager, Mikenna Smith, performed crucial pesticide resistance testing this summer. Pesticide resistance testing assesses the levels at which the mosquitoes are resilient to our current pesticides allowing us to ensure that the mode of action used by the pesticide we are applying is still effective this year. None of our tested mosquito populations have shown signs of pesticide resistance to date.

Though the summer mosquito field season is complete, the TCWP team will spend the winter reviewing and analyzing all data collected in 2018. We will use this data in combination with knowledge gained in previous seasons to formulate a mosquito management plan for summer of 2019.


Protecting our Waterways in Jackson Hole

Jackson Hole Clean Water Coalition

Living in Jackson,  it can be easy to take for granted the immense natural beauty that surrounds us on a daily basis-from the towering Tetons raising above our valley floor to the seemingly pristine waterways that meander through our collection of small towns. We all have a role to play to help maintain and increase the vitality of our surrounding rivers and streams. Through various initiatives, the Jackson Hole Clean Water Coalition is working towards protecting and improving the water quality in Teton County.

Looking to do your part? Check out the following two initiatives below and learn how you can protect waters that flow through your property and get involved in restoration of the Flat Creek watershed.


Purpose: To protect the health of the Upper Snake River watershed and the clean water its trout and wildlife depend upon through small changes that every homeowner can partake in (outlined below).

What you can do: Get certified! Through the Trout Friendly Lawns Certification Program, you can fulfill a four step process that will not only aid in the preservation of our waterways but also, gives you a chance to win from over $1,500 worth of prizes (and everyone loves prizes!).

  1. LIMIT FERTILIZER AMOUNTS – instead of blanket covering of your lawn with fertilizers, learn what is the most effective for your type of vegetation and use sparingly; overspray does more harm than good for your plants and ends up running off into surrounding waterways. Organic is best and slow-release organic is even better! 
  2. BE WATER-WISE – many unknowingly over-water, causing runoff and the leaching of nitrogen from the soil before entering the groundwater.
  3. PLANT NATIVES AND MAINTAIN STREAMSIDE BUFFER – Native plants are conditioned to grow in our local environment, which means they need less tending, watering, and fertilizer! Need help knowing what is native to our area? Contact TCWP, we are happy to offer suggestions.
  4. USE HERBICIDES AND PESTICIDES APPROPRIATELY – let us help you! Utilization of the correct types and amounts of herbicides/pesticides is a main goal of Teton County Weed & Pest. We are here to complete assessments of your property and help you navigate the world of invasive species (contact TCWP).

Flat Creek Watershed Management Plan

Purpose: To restore water and habitat quality in the Flat Creek watershed by reducing contaminant loads, enhancing aquatic habitat, and generally improve fishery and recreational potential.


  1. WATER QUALITY GOAL– Restore water quality in Flat Creek to meet the state’s designated uses for the waterbody.
  2. RIPARIAN HABITAT GOAL – Protect and restore riparian habitat (banks of the river) along Flat Creek and its tributaries.
  3. AQUATIC HABITAT GOAL – Improve aquatic habitat in Flat Creek to maintain native trout populations.

What you can do: Currently, the Flat Creek Watershed Management Plan is under review to re-prioritize practices and policies to continue to protect and correct Flat Creek. Have a suggestion or want to be a part of the process? Head to JH Water Coalition website to see status updates and submit your input.


Weed of the Month: Cheatgrass Treatment

Invasive Species: Cheatgrass (Bromus tectorum L.)

Cheatgrass is an annual or winter annual invasive grass that can grow anywhere from 4-to-30 inches high with dense hairs on its leaf sheathes. Cheatgrass also has an early lifecycle which allows growing to begin immediately after the snow melts.

In Teton County, it begins to cure out by June, and by mid-June or July it has completely dried out. This aggressive, quick-growing life cycle not only gives it a competitive advantage over other plants and allows to completely choke out other native plants in the area.

Adding to cheatgrasses devastating qualities is the fact that it is only palatable in the early stages of the life cycle. Once past this stage, cheatgrass becomes an increasing fire hazard issue as it dries out and creates vast amounts of biomass/leaf litter.

Control Options

  • Small Patches: Hand-pulling
  • Spring Treatment (while green and before seeds are produced): Roundup
  • Fall Treatment: Laramie

Laramie Treatment Option

  • Active ingredient is rimsulfuron, which is in the same family of herbicides as Telar and Escort.
  • Previously sold as Matrix
  • Works by killing late season second wave plants and by preventing germination the following spring
  • When treating, apply to both the ground in and immediately around patches and growing cheatgrass directly with Laramie.
  • Must have an incorporating precipitation event within 3 weeks of application. Usually treatments can begin in late September and continue until snow starts to accumulate.



Herbicides, What to Use and What to Avoid

The Lowdown on Herbicides

Always Read the Label Before Applying Herbicides

There are currently 19 families of herbicides and thousands of different formulations and brand names available, which can make deciding which product to use seem daunting. To help streamline the process, TCWP only carries products that treat species listed on the State Designated and County Declared Lists.

Basic Classification of Herbicides

Auxin Mimic Herbicides

Chemical Names: Aminopyralid (Milestone & Opensight), 2,4-D (Speedzone & Weedmaster/Rangestar), & Dicamba (Speedzone & Weedmaster/Rangestar)

Common Use Names/Product Names: Milestone, Opensight, Speedzone, Weedmaster, or RangeStar (read on for specific uses for each brand)

Mode of Action & Best Uses: Auxin Mimic Herbicides work particularly well on herbaceous, broadleaf plant species, and have limited control of some annual grasses. They cause the plant to undergo rapid, uncontrolled growth, which eventually kills the plant.

Milestone and Opensight can be used in noncrop, natural areas, and rangeland. They provide residual control for germinating seeds. These products should not be used within the drip line of conifers, or to vegetation that may be composted, or used on desirable vegetation.

Speedzone does not provide residual control that Milestone and Opensight provides, but it is a good alternative for treatments in lawns.

WeedMaster – In instances when grass hay will be used on desirable vegetation, Weedmaster provide control of broadleaf species without impacting desirable vegetation through hay or manure.

ALS inhibitors

Chemical Names: chlorsulfuron (Telar), metsulfuron-methyl (Escort & Opensight), rimsulfuron (Laramie), and imazapic (Plateau)

Mode of Action & Best Uses:  Inhibit branch chain amino-acid synthesis or acetolactate synthase (ALS) inhibiting herbicides, also referred to as acetohydroxyacid synthase (AHAS). Controls many broadleaf species, some grass species, and some shrubby species. Not for use in lawns.


Telar (Chlorsulfuron)

Best Uses:  Best for most of TCWP listed species because it is very effective and less harsh on non-target plants than Escort – toadflax, hoary alyssum, field bindweed, houndstongue, common mullein

Escort & Opensight (Metsulfuron-methyl)

Best Uses: Works well on most TCWP listed species, but can have more non-target damage on desirable grasses and shrubby species (such as willow and sage).

Laramie (Rimsulfuron)

Mode of Action: Cheatgrass control – in September/October this can be used as a replacement for Telar in a tank mix with Milestone to control more listed species when also treating cheatgrass. 


Plateau (Imazapic)

Mode of Action & Best Uses: Much less selective that the other listed herbicides. Controls cheatgrass, but also impacts non-target grasses, forbs, and potentially trees if applied incorrectly.

EPSP Synthase Inhibitors

Chemical Name: glyphosate (Roundup)

Mode of Action & Best Uses:  Inhibit branch chain amino-acid synthesis or acetolactate synthase (ALS) inhibiting herbicides, also referred to as acetohydroxyacid synthase (AHAS). Controls many broadleaf species, some grass species, and some shrubby species. Not for use in lawns.

Roundup (Glyphosate)

Mode of Action & Best Uses: Inhibits 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase which is needed for protein systhesis. A non-selective herbicide. Excellent for “bareground” control (eg driveways and walkways). Can be used under the dripline of trees to treat invasive species without impacting the tree.

Diving into the world of herbicides can be a bit overwhelming, but that is what TCWP is here for. For advice on controlling invasive species, herbicide questions, or for a free consultation of your Teton County residence, please contact Teton County Weed & Pest District at 307-733-8419.

Weeds of the Month: Dalmatian and Yellow Toadflax

Never Judge a Plant By the Beauty of its Flower

By now you probably know that not all noxious weeds look the part. Some are quite pretty. But weeds are not designated as noxious because of the way they look – it is the way they ACT that counts.

snapdragon-like flowers
Individually, these snapdragon-like flowers may look pretty. But if you let them loose on your property, you will most certainly NOT find them pretty for long. 


Dalmatian and Yellow Toadflax

Dalmatian Toadflax and Yellow Toadflax (click to learn more) are two noxious weeds that have tricked many landowners into letting them onto their property because of their beauty. The yellow snapdragon-like flowers that the Figwort family is known for are an attractive addition to yards in Wyoming. They don’t require pampering either. Before you know it, your entire property will be filled with these stout perennials and you won’t see much else. If either of the toadflaxes get to that point of coverage, your only option is biannual herbicide treatment with one of the few herbicides that these hardy species are susceptible to.

Yellow toadflax (left) and Dalmatian toadflax (right) have identical flowers but can be distinguished by their leaves. Dalmatian has broad waxy leaves while Yellow has long narrow leaves.


Why is toadflax consider noxious?

Remember, noxious weeds are given that designation because of how they act. Specifically, they cause harm to ecological systems and/or agricultural systems by invading established plant communities and replacing what was growing there, whether it was a crop or a native bunchgrass meadow. The twin toadflaxes are successful invaders due to their creeping perennial root system that allows them to steadily spread and squeeze out competitors. They are difficult to eradicate because their extensive root systems exclude mechanical control, their waxy leaves act as a barrier to foliar herbicides, and their long-lived seeds assure that they will be back, even if you do manage to kill them.

Dalmatian ToadflaxDalmatian toadflax is seen here crowding out native fireweed (pink in the foreground) and buckwheat (whitish-pink in the background)
Dalmatian Toadflax What’s wrong with this picture? All the invasive Yellow toadflax in front of the Tetons! 


TCWP has found some success with herbicides containing Chlorsulfuron, as long as a good surfactant is used to help the aqueous solution penetrate the waxy leaves. We are also hopeful about Mecinus janthiniformes, a stem-mining weevil that is showing promise as a bio-control agent. Bio-control is especially critical on the steep slopes in Teton County where toadflax likes to grow.

Dalmatian Toadflax LeavesThe waxy leaves of Dalmatian toadflax provide a barrier to most foliar herbicides.

So next time you are looking for pretty flowers to decorate your yard, learn about their different personalities before you purchase. Aggressive plants may be easy to grow in the short-term, but they will cost you in the long-term when you are trapped in an indefinite biannual herbicide treatment schedule. Be aware of what you plant in your yard as well as what you already have growing there that might have moved in from outside. Bring any suspects into our office and we will identify them for you and let you know if you have anything risky. And remember, don’t judge a plant by the beauty of its flower.

Other noxious beauties to look out for!
Mosiac - Teton County Weed & Pest Article

Tetons 2020 – Mosaic

2018’s Mosaic – The State of the Tetons Ecosystem

Mosaic, a creation from The Charture Institute, came out of last year’s Tetons 2020 effort, with the final piece featuring 16 essays diving into various aspects of the health of the Teton County region’s ecosystem.

“The concept behind Mosaic is to begin assembling pieces of information we already have into a clearer understanding of our ecosystem.  With luck, it will also help catalyze further pursuit of the Jackson/Teton County Comp Plan’s vision: Preserve and protect the area’s ecosystem in order to ensure a healthy environment, community, and economy for current and future generations.”  – Jonathan Schechter

The Charture Institute, based out of Jackson Hole, Wyoming, is a think tank focused on growth, change, and sustainability in Places of Ecological and Aesthetic Significance.

Mosaic_SinglePage of Article

Teton County Weed & Pest District’s Perspectives on Invasive Species, written by our own Mark Daluge & Erika Edmiston, featured in this year’s Mosaic highlights the health and maintenance needed to protect the Greater Yellowstone Ecosystem from active and potential invasive species (read the complete article here)

  • Invasive species hold the potential to create great environmental and human health issues, and are costly to address.
  • Human behavior is the major factor affecting the introduction and spread of invasive species.
  • Despite active prevention and treatment efforts, over 24,000 acres in Teton County, Wyoming — roughly one percent of its land — are affected by invasive species.
  • Practice the outdoor ethic of PlayCleanGo – Stop invasive species in your tracks!
  • Create invasive species management plans for all development over ¼ of an acre, as required by the Teton County LDRs
  • Pay attention to plants that look out of place and report them. Curiosity is our friend!
  • Do your part! Every landowner in Wyoming is required by State Statute to treat noxious weeds on their land.


To view the full 2018 Mosaic, please click here!

Biological Control in Teton County

Biological control is the introduction of a natural enemy or predator to control an invasive weed or pest. One reason invasive weeds may proliferate so well in a new environment is due to the potential limitation or lack of organisms that will attack or consume that plant. Native species, on the other hand, are in equilibrium with their natural enemies and as such, their populations are kept in check.

Biological control agents released in the United States must first go through years of rigorous testing following guidelines established by the United States Department of Agriculture’s Animal and Plant Health Inspection Service – Plant Protection and Quarantine (USDA-APHIS-PPQ). These tests are performed to ensure a potential agent is host-specific, that is, they only feed and develop on the target weed and will not attack natives.

When to Use Bio Control

Biological control is used in an integrated pest management plan. A weed infestation may be too large to affordably treat chemically and biological control may be an initial treatment option to knock a weed population down to where it can be sprayed or mechanically controlled. Additionally, biological control is often used on steep slopes which would be inaccessible to a spray crew with their equipment, but a bio agent could be released at the base of such a slope. We also release bio agents on banks and islands along the Snake River that are accessible by raft.

Bio Agent Status in Teton County

We have bio agents on musk thistle, dalmatian and yellow toadflax, spotted knapweed, leafy spurge, common mullein, and St. Johnswort. We have biological control agents on Canada thistle as well, but their effectiveness has been limited throughout the Western U.S.

A spotted knapweed agent working well in Teton County is called Larinus minutus, the lesser knapweed flower weevil. Larvae feed on pappus hairs, seeds, and receptacle tissue. A single larva can completely destroy a knapweed seed head! One study found that if the weevil density was high enough, a knapweed seed bank could be exhausted in seven years (Knochel, et al., 2010).

Far right seed head: gall formed by Larinus minutus, the lesser knapweed flower weevil.

Emerging Larinus minutus adult. Image credit: Rachel Frost, Montana State University.

During late summer, adults chew their way out of the galls, leaving behind distinct holes in the flower heads.
Adult Rhinocyllus conicus, thistle seed head weevil. Image reference:×512/0580019.jpg


Rhinocyllus conicus, the thistle seed head weevil, attacks musk thistle by burrowing into seed heads and consuming seeds and receptacle tissue while in the larval stage. This agent has established quite well in Teton County and their damage is easily noticeable by breaking open a flower head.

A musk thistle flower head revealing Rhinocyllus conicus larval feeding damage to seeds and receptacle.
Musk thistle attacked by Rhinocyllus conicus. Seeds have been consumed and only seedless plumes are left behind.


Dalmatian toadflax is host to an agent called Mecinus janthiniformis, a stem mining weevil. Adults feed on foliage and can cause shoot stunting as well as flowering and seed production suppression. Larval mining of the stem impairs water/nutrient transport, causing desiccation and reduces resources stored in the roots.

Adult Mecinus janthiniformis in a toadflax flower. Image reference (link in image)

Mecinus janthiniformis larva mining a dalmatian toadflax stem.
Adult Mecinus janthiniformis overwinter in the stem, emerging in the spring to begin feeding and mating.


Knochel, D.G., Monson, N.D., Seastedt, T. R. (2010). Additive effects of aboveground and belowground herbivores on the dominance of spotted knapweed (Centaurea stoebe). Oecologia 164 (3), 701-712.

Spotted Knapweed

August’s Weeds of the Month: Field Bindweed & Spotted Knapweed

Weed of the Month, Number 1: Field Bindweed

Field BindweedField bindweed, a native of Eurasia, is thought to have been introduced into the US through contaminated seed as far back as 1739. This vine species forms a monoculture by climbing and twisting its way up anything and everything keeping other plants from reaching light.

Field Bindweed
Field Bindweed

Field bindweed is a rhizomatous perennial. Its roots can reach down nearly 14 feet in its search for moisture. As the roots grow away from the parent plant, new shoots are formed creating new plants. This species can grow up to 10 feet in a growing season. Each of its morningglory flowers produce two seeds which may be viable for more than 60 years!

Because field bindweed is a rhizomatous perennial, hand pulling is not an effective control option. Heavy cultivation may be effective if repeated frequently throughout the growing season. Solarization may have limited success because the temperatures required for control are difficult to sustain in our environment. Herbicides are also an effective part of any integrated control plan for field bindweed.

Field Bindweed, what to look for?
  • Deeply rooted perennial vine that typically grows along the ground until finds a structure or other plant to climb
  • Smooth, arrowhead-shaped leaves
  • Long, slim, winding stems
  • Trumpet-shaped flowers, typically light pink to white
  • Two small leaves about an inch below the flower
  • Pale roots

Weed of the Month, Number 2: Spotted Knapweed

Spotted knapweed, like many of the invasive species in Teton County, originated in Eurasia. It was first identified in the US in the late 1800s in Washington, and it is thought to have been a stowaway in a shipment of alfalfa. It forms dense stands by both out competing other species and by exuding a chemical into the soil that inhibits germination of  neighboring plants. It’s primary means of spread is its seeds, which are dispersed by wind, gravity, and animals.

Spotted Knapweed
Spotted Knapweed

Spotted knapweed is a taprooted, biennial species. In its first year of growth rosettes are formed, but it does not begin to form flowers until its second year of growth. In some instances, spotted knapweed may take on more a perennial habit and grow a third season.

Because spotted knapweed has a taproot, it can be effectively managed by hand pulling; however, gloves and long sleeves are recommended because it can cause skin irritation. Dense infestations may be best controlled with herbicides to reduce soil disturbance.

Spotted Knapweed, what to look for?
  • Resembles a thistle but has no spines
  • Vertical branched stems, can reach heights of 5 feet tall when flowering
  • Flower heads are small and oval
  • Light purple to brilliant pink thistle flowers
  • Leaves at base of thistle-like flower (called bracts) have triangular black spots
  • Leaves: medium-green with a silvery gray


Giant Hogweed

Giant Hogweed and Cow Parsnip: Which is Which and Why You Should Care

This summer we fielded calls from several frantic landowners who were certain they had giant hogweed growing on their property. Heracleum mantegazzianum is a weed worthy of panic, as its sap causes severe phytophotodermatitis in humans. When skin is exposed to the sap and subsequently exposed to the sun, it will redden, swell, and form painful blisters that resemble burns and often leave scars. If the sap gets in your eyes it may cause permanent blindness. Fortunately, giant hogweed does not live in the Rocky Mountain States. But its close relative, Cow Parsnip (Heracleum maximum) does.

Giant Hogweed History

Giant hogweed is native to Asia and was introduced to New York State as an ornamental in the early 1900s. Due to its “Dr. Suessian” charm, it became a popular addition to hobby gardens in coastal areas throughout North America. When it became evident that giant hogweed could spread into natural environments and displace native plants, and that its caustic sap made it hard to remove, it was classified as a federally listed noxious weed that was illegal to buy or sell.

Giant Hogweed in America

When giant hogweed was first discovered growing in Virginia this summer (2018), the news spread like cheatgrass, igniting a frenzy on social media about the spread of an invasive weed that “burns and blinds.” The news reached Teton County around the flowering time of a closely related native plant called cow parsnip. Many residents mistakenly identified the cow parsnip as giant hogweed, and our phones started ringing.

Spot the Similarities

Cow parsnip, Heracleum lanatum, shares the family AND genus of giant hogweed, and therefore shares several diagnostic traits with it:

  • White flowers arranged in umbels (umbrella-like clusters)
  • Leaf bases that form sheaths around the main stalk
  • Large leaves that are divided into leaflets
Spot the Differences

But there are also some BIG differences between these two plants. Cow parsnip is a rather large plant, reaching heights of over 7 feet tall and sporting leaves that are 2.5 feet in diameter. But giant hogweed dwarfs the cow parsnip, topping out at 14 feet tall with leaves spanning 5 feet across!

Cow parsnip stalks are about 1 inch in diameter and solid green, while hogweed stalks can be 2.5 inches in diameter and are mottled with reddish spots, just like another member of the carrot family, poison hemlock.

Speaking of poison, the family that these plants share (apiaceae, a.k.a. the “carrot family”) is infamous for including some of the deadliest plants on Earth. Both poison hemlock and water hemlock are in this family and ingesting a small amount of any part of these plants will kill a human. Those that don’t kill can burn and blind, like giant hogweed. Even our native cow parsnip is not totally benign. It has been reported to cause phytophotodermatitis reactions as well, though not nearly as severe as those caused by giant hogweed. In the plants’ defense, the reaction is caused by furocoumarin chemicals in its sap that evolved to defend the plant against herbivorous insects. We were not the intended target. Also, there are several friendlier members of this family that we couldn’t do without, including parsley, dill, cilantro, and, of course, carrots. But it is safe to say, plants in the carrot family should be treated with caution whenever encountered outside of the grocery store, unless you are sure of their identity.

The take home message is, learn to recognize plants in the carrot family (remember, umbels and divided leaves), be cautious around any plant you are not familiar with (you don’t want to be the unintended target of an arms race between plants and insects), and have compassion for our coastal friends who have to live with giant hogweed and poison oak. Our stinging nettle pales in comparison.

View the Difference

Cow Parsnip
Giant Hogweed

Both plants have large leaves dissected into 3 leaflets, but leaflets of cow parsnip (left) have rounded lobes and giant hogweed leaflets (right) have pointed lobes. Also, giant hogweed leaves are twice the size of cow parsnip leaves.


Both cow parsip and giant hogweed have white flowers arranged in umbrella-like clusters called umbels, but the differ significantly in size.


Cow parsnip resembles giant hogweed but is much smaller, lacks the red spots on the stems, and is far less dangerous.

Giant hogweed

Giant hogweed stalks are mottled red like its close relative poison hemlock. Cow parsnip stems are solid green.

Giant Hogweed Burns

The sap in giant hogweed contains furocoumarin chemicals that cause phytophotodermatitis in humans.

Giant Hogweed

Giant hogweed is a federally listed noxious weed due to its ability to displace native plants and its caustic sap.

Gros Ventre River Spray Days 2018

2018 Gros Ventre River Spray Days

19th Annual JHWMA Gros Ventre River Spray Days: 3 days, 40 people

The Jackson Hole Weed Management Association (JHWMA) hosted the 19th Annual Cooperative Noxious Weed Spray Days (July 17-19, 2018).  Volunteers came from all around Teton County and as far away as Idaho Falls to team up for invasive species weed control along the Gros Ventre River.  Organized by Grand Teton National park and Teton County Weed and Pest District, the group targeted spotted knapweed, Dalmatian toadflax and perennial pepperweed (click on weeds to learn more about these invasive species) on public lands along the river corridor.  The invasive weeds treated compete with native vegetation, adversely impacting wildlife habitat, and transforming ecosystem function.

Gros Ventre River Spray Days 2018 - Invasive Species Control

The first indication of knapweed on the Gros Ventre River is briefly discussed in minutes from a Weed and Pest District Board meeting in 1974, though the exact location is not mentioned.  In 1999, JHWMA partners decided it was important to begin recording the presence of noxious weeds throughout Teton County. The Gros Ventre River from the Goosewing Ranch area to the confluence with the Snake River was surveyed as part of this effort. At that time, spotted knapweed was only located as far upstream as the Forest/Park boundary. No other infestations were identified upstream (east) of this location. This prompted the beginning of what is now known as the JHWMA’s Annual Gros Ventre River Spray Days project.

Gros Ventre River Spray Days 2018 - Invasive Species Control

In 2000, crews from Grand Teton National Park, the Bridger Teton National Forest, Teton County Weed and Pest, and the National Elk Refuge began targeting spotted knapweed along the river corridor in the hopes of reducing and containing the infestation and keeping the infestation from spreading further east into the Gros Ventre area.  Despite these efforts, in 2001 spotted knapweed was found between the Forest/Park boundary and Lower Slide Like on the Gros Ventre Road. Then in 2008, it was found in the campground at Lower Slide Lake. This indicates that in addition to traveling downstream, knapweed is also traveling up the road with humans (vehicles, horses, snowmobiles, UTV’s, etc).  This movement highlights the importance of public awareness of how we can prevent the spread of invasive species to our favorite recreation areas by following PlayCleanGo ( principles.

Gros Ventre River Spray Days continues to be integral to the protection of wildlife habitat in Grand Teton National Park and the National Elk Refuge. Unfortunately, the spotted knapweed infestation is so extensive in this corridor that it will never be eradicated. However, with careful planning and targeted treatments, JHWMA partners are containing and reducing the infestation. Annually, crews treat roughly 50-100 acres of invasive species in this 1,200+ acre project area, thanks to grant funding and dedicated funding from agencies.

Gros Ventre River Spray Days 2018 - Invasive Species Control

Agencies, organizations, and businesses that have assisted with the project over the years include but are not limited to:

Fremont, Lincoln, Natrona, Park, and Teton County Weed and Pest Districts in Wyoming, Bonneville and Teton County Weed Districts in Idaho, Jackson Hole Fire/EMS, Boreal Property Management, Jackson Hole Property Services, Intermountain Aquatics, the Bridger-Teton, Custer Galatian, and Shoshone National Forests, the National Elk Refuge, Yellowstone and Grand Teton National Parks as well as the National Park Service – Northern Rockies Exotic Plant Management Team.  The Bureau of Land Management, Wyoming Department of State Lands, Jackson Hole Land Trust, Hanna Outfitting, Gros Ventre River Ranch, Jackson Hole Golf and Tennis, Teton Conservation District and the Rocky Mountain Elk Foundation.

The JHWMA was formed in 1998 to establish common long and short-term management policies, goals, and objectives necessary for cooperatively managing and funding noxious weed activities across all jurisdictional boundaries.  To learn more about the JHWMA, please visit