Invasive Weeds

“We live in this beautiful state because of the vistas and the recreational opportunities the land provides. Noxious invaders are the greatest environmental threat to the Montana we know today.”
Montana Weed Control Association

How do noxious and invasive weeds threaten the Pryors and other natural landscapes?»

What are Invasive and Noxious Weeds?»

Reports on Volunteer Noxious Weed Control Efforts - Summer 2013 »
Click to volunteer for summer 2014 weedpull

How can you help prevent new weed infestations in the Pryors?

Vehicles and Weeds?

The following are four weed species of concern in the Pryors
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Spotted Knapweed:
More information and photos:
MT Fieldguide
MT Weed Control Association

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Houndstongue:
More information and photos:
MT Fieldguide
MT Weed Control Association

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Leafy Spurge:
More information and photos:
MT Fieldguide
MT Weed Control Association

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Canada Thistle:
More information and photos:
MT Fieldguide
MT Weed Control Association

INVASIVE WEEDS IN THE PRYORS
Revised from a presentation by Clayton McCracken, Pryors Weed Campaign
April 4, 2013 – Montana Audubon Conservation Center
BioBlitz leads to Pryors Weed Campaign»
Crooked Creek Road Corridor: Mustard Weeds and Canada Thistle»
Spotted knapweed infestations in the Pryors »
Hounds tongue infestations in the Pryors»
Leafy Spurge found on Burnt Timber Ridge»

Notable Weed Infestations in the Pryors

“Noxious weeds threaten the habitat of wildlife by altering natural communities. Noxious weeds can wipe out the native vegetation for nesting, food and cover needed by birds, mammals and fish.”
Montana Weed Control Association

“Noxious weeds are plants that have been imported from other areas, so they have no natural biological controls. As a result, they are spreading like wildfire, outcompeting and displacing many native plants. It is estimated that we are losing about 5,000 acres per day across the west to weeds. Their seeds are spread by wild animals, domestic livestock, pets, people and vehicles. In Montana alone spotted knapweed is estimated to cost $42 million dollars each year in control efforts, crop and forage losses, land rehabilitation, and loss of wildlife habitat.” Montana.plant-life.org Read more….
“Noxious Weeds: Plants species that are deemed to be invasive and possess the capacity to negatively impact the state’s natural vegetation communities and agricultural lands. Only species which are introduced (not native) to Montana may be designated as Noxious Weeds. Noxious Weeds are defined in state law as exotic species which may render land unfit for agriculture, forestry, livestock, wildlife, or other beneficial uses or that may harm native plant communities….”Montana Field Guide


Last July, 80 experts and citizen scientists gathered on the shoulder of Red Pryor for a BioBlitz.
The botany team lead by Jennifer Lyman found 336 species of plants, 27 of which were not native to North America.

What really struck us was the proliferation of weedy plants over what we had seen in previous years. By the end of the BioBlitz we had gone from saying, “The Forest Service has to do something about those weeds.” to saying, “Dag nab it, we are going to do something about those weeds.”
The Pryors Weed Campaign was initiated right there. Jennifer Lyman, Susan Newell, Rita Harding, Dick Walton and I formed the steering committee. We are all active members in organizations within the Pryors Coalition.

As with the other efforts stemming from the Pryors Coalition our underlying goal is to support the Forest Service and BLM while urging them to focus upon the Pryors and co-ordinate their efforts.

We started right away to work with the BLM and Forest Service. Larry Padden is the point man for BLM’s weed management program. Terry Jones is for the Forest Service. We are fortunate to be working with them. Both have a background in range management giving them an appreciation of ecology. Both have served a long time in their respective positions. They know and understand the Pryors. They patiently explained their agency’s weed management program and have worked with us to find ways volunteers can help.

MWA jumped at the chance to arrange this presentation and to sponsor three weed pull days in the Pryors. Yellowstone Valley Audubon is figuring out ways to fight the weeds in Bear Canyon.

There could not be a better time than now to focus on weed infestations in the Pryors.
The Pryors Weed Campaign is focused on the 75,000 acres managed by the Forest Service and the BLM lands that skirt those of the Forest Service and include much of East Pryor Mountain.


Mustard Weeds: A Temporary Problem
When you drive down Crooked Creek Road next summer you may see roadbanks filled with weeds.
These weeds are non-native but they are serving as pioneer plants. They are starting a succession of plant communities that will, over time, evolve into the climax native plant community appropriate for that habitat.

When the Crooked Creek Road was reconstructured starting in 2010 and finishing in 2011 the roadbanks were treated very appropriately. They were contoured. Debris was scattered to prevent water damage. The banks were sprayed with a slurry of fertilizer and native grass seeds.

It so happened that in some places the soil was already loaded with seeds of non-native plants, mostly mustards. There are other mustards in the roadbanks, but field pennycress is the most abundant.

Mustard species are very effective weeds. Mustards come up early in the spring overgrowing other plants. They produce seeds even as they are blossoming on the growing tips. The seeds are abundant and can lie dormant in the soil for years.

Even so, the mustard weeds on these roadbanks will eventually die out as they are replaced by the native vegetation. The Forest Service will allow this to happen without further treatment of the roadbanks.

Let me stress though, habitat invaded by the aggressive weeds, which we will soon discuss, will not revert to the native plant community without our intervention.

The Red Waffle Fire
There is more to the story.

Where did these mustard seeds come from? They are not natives.

In July 2002 the Red Waffle fire burned the talus slopes of the eastern escarpment of Big Pryor. The fire was finally put out by a torrential rainstorm. That rainstorm washed debris from the steep hillsides down into Crooked Creek.

The Forest Service was in a predicament. What if another rainstorm occurred? Would more debris be washed into Crooked Creek? Would the Crooked Creek Road be washed out?

The decision was made to seed with native grasses the 400 acres of steep, badly burnt hillside. When the seeding was done in 2002 the hillsides had to be stabilized with mulch until the grasses could take hold. One ton of straw per acre was laid down by helicopter.

So the next spring they had a wheat crop. Not a problem. Unfortunately the straw was not weed free as requested. They also had a crop of farm weeds – the same mustards we now see on the banks of the Crooked Creek Road. They grew for a few years and eventually died out, having produced many seeds, which remained dormant until the soil was laid bare in the reconstruction of the road.

Canada Thistle
Not only were the seeds for mustard weeds brought in with the straw; seeds of Canada thistle were also.

Interspersed along Crooked Creek Road there are grassy meadows. The southeast facing slopes receive abundant sunlight. You could not find a better place to grow Canada thistle.

Here the Canada thistle grows as tall as four and a half feet over towering the grass. The patches of Canada thistle form a monoculture – a dense stand of one plant- that push out the native species.

Canada thistle, having started ten years ago, is now well established in the Crooked Creek corridor and will continue to encroach unless we take action.

Rhizomes
Canada thistle has rhizomes. That makes this thistle a gonzilla among weeds. Rhizomes are underground stems from which new shoots arise. The new shoots remain attached by the rhizomes to the initial plant, and continues to be part and parcel of that plant. Just as a grove of aspen trees are all one tree with many shoots.

Plants that reproduce vegetatively in this manner grow in an almost perfect circle with the shoots crowded together. Each growing season, the circle enlarges outwardly.

The presence of rhizomes makes Canada thistle, Leafy spurge and Dalmatian toadflax difficult weeds to eradicate.

You can not eradicate a patch of these weeds by pulling them. When you pull these weeds you invariably leave some rhizomes in the ground. Even a small rhizome piece, a quarter of an inch long, has enough stored energy to develop a new shoot.

Canada thistle is a perennial. A single plant may live for several years, each season flowering and producing seeds.

No truly effective means of biocontrol has been found. Using herbicides is the only way to control Canada thistle.

In a weed campaign it is critical to understand how weed seeds are dispersed.
The pappus of the thistle, which otherwise might airlift the seed, easily breaks off leaving the seed in the receptacle. Eventually the seed is released and falls within a few feet of the plant.

Herbicide Treatment
The principle weapon the Forest Service uses for weed management is spraying with herbicides. There is no other choice if established weeds are to be eradicated or contained. There are a few non-chemical options but those options usually have to be combined with herbicides.

The Beartooth District of Custer National Forest has its own spray crew. The crew first attends to the Beartooths then comes to the Pryors in mid August.

The optimal time to spray is when the sugars produced by photosynthesis in the leaves are being moved down the phloem to the roots. This occurs in early summer as the plant is growing, before it begins to bud.

Aminopyralid, an effective herbicide against members of the Aster family, has 94% control when sprayed on Canada thistle during the early summer growth phase. When Canada thistle is sprayed in mid-August as the plant is setting seed, aminopyalid has only 83% control one year after treatment.

The “optimal time” happens all over the county at the same time. The spray crews can not reach all sites at the “optimal time.”

No herbicide with one spraying, even applied at the optimal time, will kill all of the weeds within an infestation.

An infestation must be sprayed consistently for several growing season. The site must be monitored for years to catch seedlings from long dormant seeds.

Canada Thistle not a Custer National Forest priority
Canada thistle is not a priority for the Forest Service’s Beartooth District. However, when the spray crew goes up the Crooked Creek Road they will spray any patches along the road.

Mid August, 2012, they did a thorough job spraying both the Canada thistle and the hounds tongue on the Crooked Creek Road.

Mid August is not the optimal time to spray Canada thistle. The thistles are setting seed and the flow of energy is going to the seed heads not down into the roots. June, just before the thistles bloom and mid September, before a killing frost, are the windows of opportunity.

In general if a weed is sprayed after it flowers and begins to set seed, those seeds will continue to develop and be the source for a new generation.

The patches of Canada thistle in the Crooked Creek corridor, that started ten years ago a distance from the road, have now edged up to the road. Now seeds dropped along the road are being picked up on tires of vehicles and carried further up the road, even beyond Big Ice Cave.

Let me state that I am not an alarmist. The sky is not falling. But if not stopped, Canada thistle will take over the Crooked Creek corridor. It is more cost effective to eliminate a small infestation than it is to contain a larger well-established infestation.

The Pryors Weed Campaign urges the Forest Service to undertake a treatment plan to eradicate Canada thistle in the Crooked Creek corridor. We are working with the Beartooth District of the Custer National Forest on some options.


Burnt Timber Ridge Road
The road up Burnt Timber Ridge has become a popular way to get to the top of East Pryor. Midway up the ridge, the road ascends more gradually through an area called Cheyenne Flats.

Here the plant community is Black sagebrush and Blue bunch wheatgrass. Limber pines grow around the openings. The BLM/Forest Service boundary goes through Cheyenne Flats bisecting this plant community.

Spotted Knapweed
Last summer (2012) Spotted knapweed appeared on Burnt Timber Ridge.

The Spotted knapweed begins to show up part way up the ridge. It is spread out, one plant here another there, a plant on the hill above the road, another down the steep hillside.

It continues sporadically along the road into the Forest Service lands. Still spread out, but now within the openings between pines.

In a Black sagebrush community there is typically open ground between plants. In those spaces knapweed seedlings can establish. Knapweed prefers exposure to good sunlight. Knapweed can and will take over.

The Pryor Mountain horses graze on Cheyenne Flats during the winter. They depend on the nutritious bluebunch wheatgrass that grows between the sagebrush. A heavy infestation of knapweed will severely reduce the grazing potential of any range land.

There are other species of knapweed that are non-native, very aggressive, invasive weeds. In the Pryors we mainly have Spotted knapweed. Spotted knapweed can be recognized by the dark bristles on the tips of the bracts.

In addition to simply overgrowing other plants there is another reason knapweeds are aggressive invaders. Their roots exude a substance that inhibits the growth of other plants – actually destroying the roots that it contacts.

As the network of the native grass roots is lost, having been replaced by the taproot of the knapweed, the water storage capacity of the soil decreases and soil erosion increases.

Spotted knapweed seeds are not airborne. As the seed head dries, the bracts open outwardly. With any motion the seeds can be flicked for up to three feet. One source states that the seeds may become attached to a passing animal, say a horse, and be carried further. Seeds can be carried still further when attached to vehicles.

Knapweed Rosettes and Bolting
Knapweed, like some other biennial and perennial plants, bolts during their second season of growth.

In the spring a seed germinates, produces a seeding, which becomes established and grows into a rosette. The plant remains in that state the rest of the season. The rosette hugs the ground. Looking down on it, the many leaves are arranged much as the petals of a rose. The leaves are coming off the stem’s nodes as you would expect. However the spaces between the nodes are very short. It is not until the plant has overwintered that those internodal spaces elongate and raise the plant’s flowering parts high off the ground. This elongation of the internodes is called bolting.

It is important to recognize the rosette stage of our aggressive weeds. You get a star if you dig out a rosette.

Knapweeds are perennials. An individual plant may live three to five years.

Once weeds appear the BLM and Forest Service resort to their one weapon. You see a weed; you spray it with a herbicide. There are reasons for that approach – nothing wrong with the agencies doing that.

Hand Pulling
There are other ways to control weeds besides relying entirely on herbicides. One way is to remove the weeds manually.

Among our major invasive weeds, knapweed is one that can be effectively controlled by hand pulling. Spotted knapweed does not spread by rhizomes. Weeds that spread by rhizomes can only with great difficulty be controlled by hand pulling.

When hand pulling it is essential to remove the crown of the plant. The stems come off the crown, which is the portion of the plant just above the beginning of the root.

If the stem is merely broken off or cut and the crown remains, a new shoot will sprout fourth.

Hand pulling knapweed works best in those early infestations where the plants are relatively few and spread out.

Volunteers can help
The federal agencies are not organized in a way they can hire a crew to pull weeds for a few days. This is where volunteers can be invaluable. Now with volunteers from MWA and other organizations, weed pulls can be done in the Pryors.

Any new infestation of invasive weeds should be aggressively treated and eradicated. The goal for treatment of the Burnt Timber Ridge knapweed has to be eradication. A determined effort of pulling and spraying with herbicide must be done this summer. The infestation crosses the boundary line. BLM and Forest Service must coordinate actions and strive together for eradication.

Sage Creek
There is a well established and spread out knapweed infestation as one enters Forest Service land on Sage Creek.

The goal for treatment of the Sage Creek knapweed may have to be containment. Along the advancing front the knapweed should be contained by hand pulling. All the knapweed within fifteen feet of the road should be removed to decrease the likelihood of vehicles dispersing the seeds. The denser patches in the center of the infestation may be best treated with herbicides. This is the approach used to contain an infestation. This has to be done yearly, forever.

The participation of volunteers in the eradication or containment of Spotted knapweed in the Pryors is critical.


Forget-me-nots are one of our favorite flowers in the Pryors. The seeds in this family occur as four nutlets with projections. A foreign relation is Hounds tongue.

The projections on the Hounds tongue nutlets are hooks. These catch onto what ever walks by. If you take your dog on outings in late summer, you probably have had the experience of combing out these seeds.

Hitch hiking is a very effective way to disperse seeds. Cattle grazing in the area can disperse the seeds.

Because the seeds of Hounds tongue are picked up and carried away from the plant, the next generation is dispersed over a wide area.

The plant is a biennial. After the seed germinates a seedling is established which grows into a rosette. There it sits over winter. The next summer it bolts into a flowering plant of about three feet.

Hounds tongue is now spread up and down the Forest Service’s portion of Crooked Creek Road. It is also found on Red Pryor and in Bear Canyon.

We want to stop its continued spread. Hounds tongue is not a priority weed for the Forest Service’s Beartooth District. They will spray it as they spray the roadsides.

We can help control Hounds tongue by pulling it.


A patch of Leafy Spurge was found by the roadside at Cheyenne Flats in July 2012 This is the first time Leafy spurge has shown up on Burnt Timber Ridge – or anywhere on the southern slopes of the Pryors.

The dense patch is limited to the roadside. At this spot a long puddle of water remains in the roadbed until early summer. It is not a mud hole. It has a firm bottom. Few people know that. They fear that their vehicle will become mired in mud. Gunning their engine, they race through the puddle spraying water far and wide. On one pass leafy spurge seeds were washed from a vehicle onto the roadside.

Leafy spurge is of considerable concern because it will take over. Once established, it is difficult to eradicate.
Leafy spurge is one of the first plants to emerge in the spring. The early and rapid growth gives it a competitive advantage.
Seeds are borne in pods. After the seeds have matured, the seedpods burst explosively and throw seeds up to 15 feet from the parent plant.

Like Canada thistle, leafy spurge has rhizomes. These rhizomes may grow more than 15 feet out from the parent plant. After treatment with herbicides the vicinity of the patch has to be carefully monitored for new shoots from the rhizomes.

The Carbon County Weed District will place special emphasis on spraying this patch in 2013. Positioned by the roadside as it is, it is sure to be spread by vehicles.

When the MWA team goes up Burnt Timber on the 29th of June 2013, they will be looking for other new starts of leafy spurge – perhaps spread from this initial patch.