Ecologically Based Integrated Weed Management to Restore Plant Diversity

Final Report for SW03-056

Project Type: Research and Education
Funds awarded in 2003: $121,750.00
Projected End Date: 12/31/2007
Matching Non-Federal Funds: $15,000.00
Region: Western
State: Montana
Principal Investigator:
James Jacobs
Montana State University
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Project Information


Management treatments for spotted knapweed were evaluated on two ranches in Montana from 2003-2006. Treatments assessed were sheep grazing, biocontrol, native seeding and tillage. Spotted knapweed and cheatgrass densities, and occurrence of all native and non-native species was recorded. Grazing by sheep showed the largest decrease in spotted knapweed densities. Surprisingly, densities of spotted knapweed did not decrease after the release of the weevil Cyphocleonus achate. Seeding of native grasses and forbs was not successful when broadcast without disturbance, or with light disturbance provided by sheep, but it was successful after shallow tillage where blue-bunch wheatgrass densities increased significantly and cheatgrass densities remained similar.

Project Objectives:

Objective 1) Integrate weed management strategies on spotted knapweed infested rangeland to address the three causes of succession based on site conditions, whole-ranch management objectives, and available ranch resources.

Objective 2) Conduct rangeland ecoassessments to determine the effects of ecologically based management on controlling spotted knapweed and restoring native plant communities.

Objective 3) Determine the economic implications of incorporating ecologically based weed management into ranching systems.

Objective 4) Conduct educational programs for ranchers and agency personnel on ecologically based whole ranch management and disseminate the results through field tours, the popular press, and the scientific literature.


Non-indigenous plant species (NIS) invasions are one of the most serious environmental threats, with NIS already having caused alteration of the earth’s biota, disruption of evolutionary processes, and change in species abundance, including extinctions (Cronk and Fuller 1995; Rhymer and Simberloff 1996). Additionally, these alterations are a threat to global biodiversity, second in impact only to direct habitat destruction (Walker and Steffen 1997). Plant invasions can occur when species are transported, either naturally or through facilitation by humans, from their home range to new locations, where they subsequently proliferate, spread and persist (Elton 1958; Mack et al. 2000). Invasions have occurred throughout time, but the magnitude in number, geographic scope and frequency have increased drastically and in direct proportion with expanding anthropogenic transport and commerce (Wells et al. 1986; di Castri 1989; Mooney and Cleland 2001). In the western states, NIS have serious ecological, economic and social consequences on rangelands. Weed invasions reduce agricultural production and the quality of life on ranches, reduce species diversity on wildlands, and affect the way ecosystems function to cycle nutrients, water and energy flow (Sheley and Petroff 1999). The economic cost of NIS in the United States, including lost revenue from crops and forage as well as the cost of management, is estimated to be $33 billion per year (Pimentel et al. 2005).

The ecological process describing plant community change is succession. Invasion by a new species is influenced by three factors: disturbance, colonization, and species performance (Pickett et al. 1987; Luken 1990). Disturbance is often suggested as a key factor in enhancing the probability of NIS establishment in native plant communities. Natural disturbance has a variety of biotic and geomorphic causes including soil disturbance by fauna, weather related events and wildlife foraging. Human disturbance includes construction and use of roads and trails, buildings, utility corridors, campgrounds and introduction and management of livestock. These disturbances create patches of either open ground, or increased resource availability, often by the removal of the existing plant community (Hobbs 1989). Thus providing “safe-sites” for NIS to invade and consequently changing the successional pathway.

Colonization success for any species depends on a number of factors including seed availability and dispersal, resource availability and a species ability to establish itself. Controlling the ability of invasive NIS to colonize is essential for establishment of healthy diverse plant communities. Functionally diverse plant communities are often considered more resistant to invasion than less diverse communities because resource availability to invading species has been reduced (Tilman et al. 1997; Fargione et al. 2003). To alter succession to achieve healthy, NIS resistant plant communities, the principals of succession are manipulated to cause plant community shifts in favor of more desirable species. The processes associated with helping to manipulate negative successional changes evaluated in this project were disturbance and colonization. The four techniques assessed were sheep grazing (disturbance), shallow tillage (disturbance), seeding (colonization), and biological control (colonization).
Spotted knapweed (Centaurea stoebe was Centaurea maculosa Lam.), a perennial forb, was introduced during the late 1800s into the Pacific Northwest from Europe as a contaminant in alfalfa seeds and ship ballasts (Sheley et al. 1998). Presently, twenty-six states list spotted knapweed as a noxious weed (Carpinelli 2005). In Montana, considered to be the distribution center in the United States (Zouhar 2001), spotted knapweed was first reported in one western county in 1926 and by 1982 every county in the state was infested at some level (Zouhar 2001; Thrift 2005). The economic costs of spotted knapweed invasion to the state of Montana is estimated at $42 million in direct and indirect costs annually with $11 million of those losses attributed to the livestock industry (Hirsch and Leitch 1996; Thrift 2005). Spotted knapweed stands are found in disturbed areas such as along roadsides, trails and over grazed rangelands. Areas of established spotted knapweed stands show a dramatic decline in species richness (Tyser and Key 1988).
Although spotted knapweed is high in nutritional value (Kelsey and Mihalovich 1987), an increase in the density of spotted knapweed decreases availability of more desirable forage species for livestock and wildlife (Watson and Renney 1974; Sheley et al. 1998; Thrift 2005). Elk and deer will consume spotted knapweed when both herd and spotted knapweed densities are high, limiting the choices in other forage (Wright and Kelsey 1997). Cattle and horses generally avoid consuming spotted knapweed in favor of grasses (Cheeseman 2006). In order to reduce the abundance of spotted knapweed through grazing, consumption by goat and sheep have been assessed. When moderate levels of spotted knapweed were present, sheep and goat grazing of spotted knapweed had a negative impact on the weed, but had a negligible effect on native grasses (Oslon et al. 1997; Thrift 2005). Although sheep did not preferentially graze spotted knapweed, aa large portion of their diet consists of spotted knapweed when present in moderate levels (Hale 2002). Sheep preference is for grazing the weed at the rosette and bolting stage. Sheep grazing can be beneficial for weed control as it can open up micro-propagule sites for establishment of beneficial native seedlings to a higher degree than mowing of fields alone (Jones and Hayes 1999). Although grazing livestock can have a beneficial impact on weed abundance, grazing alone rarely eradicates infestations. Repeated seeding of native forbs and grasses following grazing or other disturbances such as tillage increases the establishment of native species more than either grazing livestock or tillage treatment alone (Wilson and Gerry 1995). Disturbance of soil through repeated tillage can also reduce the incidence of weed germination by depleting invasive seed reservoirs (Mohler 1993; Morgan 1997; Barberi 2002; Fitzpatrick 2004), although considerable care needs to be taken to prevent invasion by annual species.
Biocontrol is a management option which can be used to reduce the intensity of a weed invasion. In Eurasia, thirty-eight insect species are known to be natural predators of spotted knapweed (Schroeder 1985). Thirteen of these species have been approved for release in the United States for use as biological control agent for spotted knapweed including Cyphocleonus achate, a flightless, root-feeding weevil (Corn et al. 2001). Larvae of C. achate feed on the root core of spotted knapweed causing considerable root damage which effectively stunts subsequent spotted knapweed shoot growth and decreases the overall vigor of the weed (Story 2004; Jacobs et al. 2006). The ability of C. achate to reduce total root biomass of spotted knapweed is dependent on its ability to colonize the root system efficiently (Steiner and Műller-Scharer 1992; Corn et al. 2006). Several years might be required after release before sufficient density of C. achate is achieved before there is a noticeable decrease in root biomass (Jacobs 2004; Corn et al 2006).

The goal of this project was to strategically incorporate disturbance (sheep and tillage), colonization (seeding and biological control) and altered species performance (sheep grazing) into the overall ranching operation in a manner that maximizes the ecological and economic benefits specifically for each ranch. We used on-farm resources (machinery and livestock) and biological controls to try to restore healthy, diverse plant communities that are resistant to NIS re-invasion.

Sustainable invasive weed management will increase productivity, sustainability, and ecosystem function, while reducing ranching costs, and therefore help to satisfy human food and fiber needs. Development of a diverse, weed-resistant plant community promotes good stewardship of natural resources, enhances environmental quality and the natural resource base upon which the ranch economy depends. Cost-effective and sustainable invasive plant management will reduce reliance on herbicide inputs, improve sustainability and economic viability of ranch operations and ranching communities, and enhance the quality of life for ranchers and the society as a whole.

Carpinelli, M. 2005. USDA-ARS, Burns, OR
Cheeseman, M. 2006. Providing supplement, with or without PEG, to reduce the effects of cnicin and enhance grazing of spotted knapweed by sheep and cattle. MS Thesis, Montana State University Bozeman, MT.

Corn, J. G., J. M. Story and L. J. White. 2006. Impacts of the biological control agent Cyphocleonus achates on spotted knapweed, Centaurea maculosa, in experimental plots. Biological Control 37(1): 75-81.

Cronk, Q. C. and J. L. Fuller. 1995. Plant invaders: The threat to natural ecosystems. London, UK, Chapman and Hall.

di Castri, F. 1989. History of biological invasions with emphasis on the Old World. In: J. Drake, F. di Castri, R. Groveset al (ed). Biological Invasions: A Global Perspective, Wiley: 1-30 New York.

Elton, C. S. 1958. The ecology of invasions by animals and plants, The University of Chicago Press.

Fargione, J., C. S. Brown, and D. Tilman. 2003. Community assembly and invasion: An experimental test of neutral versus niche processes. Proceedings of the National Academy of Science 100: 8916-8920.

Hale, M. 2002. Developing prescription grazing guidelines for controlling spotted
knapweed with sheep. M.S. Thesis, University of Idaho, Moscow, ID.

Hirsch, S.A., and J.A. Leitc. 1996. The impact of knapweed on Montana’s economy.
North Dakota State Univ. Agr. Exp. Sta., Agr. Econ. Rep. No. 355.

Hobbs, R. J. 1998. The nature and effects of disturbance relative to invasions. In: J. A. D. e. al (ed.) Scope. Biological invasions: A global perspective, John Wiley & Sons Ltd: 389-405.

Jacobs, J. S. 2004. Combining a parasite and a competitor to reduce Centaurea maculosa population density, In: Lessons of Lewis and Clark: ecological exploration of inhabited landscapes. pp. 243-344. Ecological Society of America, Portland, OR

Jacobs, J. S., S. E. Sing and J. M Martin. 2006. Influence of herbivory and competition on invasive weed fitness: Observed effects of Cyphocleonus achates (Coleoptera: Curculionidae) and grass-seeding treatments on spotted knapweed performance. Enviorn. Entomol. 35(6): 1590-1596.

Jones, A. T., and M. J. Hayes. 1999. Increasing floristic diversity in grassland: The effects of management regime and provenance on species introduction. Biological Conservation 87: 381–390.

Kelsey, R.G., and R.D. Mihalovich. 1987. Nutrient composition of spotted knapweed
(Centaurea maculosa). J. Range Manage. 40:277-281.

Luken, J. 1990. Directing ecological succession. Chapman and Hall, NY. 250pp.

Mack, R. N., d. Simberloff, W. M. Lonsdale, H. Evans, M. Clout and F. A. Bazzaz. 2000. Biotic invasions: Causes, epidemiology, global consequences, and control. Ecological Applications 10(3): 689-710.

Mooney, H. A. and E. E. Cleland. 2001. The evolutionary impact of invasive species. Proceedings of the National Academy of Sciences of the United States of America 98(10): 5446-5451.

Olson, B.E., R.T. Wallander, and J.R. Lacey. 1997. Effects of sheep grazing on a
spotted knapweed-infested Idaho fescue community. J. Range Manage. 50:386-

Pickett, S. T. A., S. L. Collins, and J. J. Armesto. 1987. Models, mechanisms, and pathways of succession. Botanical Review 53: 335-371.

Pimentel, D., R. Zuniga and D. Morrison. 2005. Update on the environmental and economic costs associated with alien-invasive species in the United States. Ecological Economics 52: 273-288.

Rhymer, J. M. and D. Simberloff. 1996. Extinction by hybridization and introgression. Annual Review of Ecology and Systematics 27:83-109.

Schroeder, D. 1985. The search for effective biological control agents in Europe. Diffuse and spotted knapweed. In: Delfosse, E. (ed.). Proceedings of the VI International Symposium on Biological Control of Weeds. pp. 103-119. Vancouver, British Columbia, Canada.

Sheley, R.L., J.S. Jacobs, and M.F. Carpinelli. 1998. Distribution, biology, and management of diffuse knapweed (Centaurea diffusa) and spotted knapweed(Centaurea maculosa). Weed Tech. 12: 353-362.

Sheley, R. L. and J. K. Petroff (ed.). 1999. Biology and management of noxious rangeland weeds, Oregon State University Press: 408-416 Corvallis, OR.

Steinger, T and H. Müller-Scharer. 1992. Physiological and growth responses of Centaurea maculosa (Asteraceae) to root herbivory under varying levels of interspecific plant competition and soil nitrogen availability. Oecolgia 91: 141-149.

Story, J. M. 2004. Cyphocleonus achates,. In: E. M. Coombs, J. K. Clark, G. L. Piper, and A. F. Cofrancesco, Jr. (eds.), Biological control of invasive plants in the United States. pp. 212-213 Oregon State University Press, Corvallis, OR.

Thrift, B. D. 2005. Summer diets of sheep grazing spotted knapweed-infested foothill rangeland in western Montana. MS Thesis, Montana State University Bozeman, MT.

Tilman, D., J. M. H. Knops, D. Wedin, P. Reich, M. Ritchie, and E. Siemann. 1997. The influence of functional diversity and composition on ecosystem processes. Science 277: 1300-1302.

Tyser, R.W., and C.H. Key. 1988. Spotted knapweed in natural area fescue grasslands:
An ecological assessment. Northwest Sci. 62:151-159.

Walker, B. H. and W. Steffen. 1997. An overview of the implications of global change for natural and managed terrestrial ecosystems. Conservation Ecology (online) 2(2).

Watson, A.K., and A.J. Renney. 1974. The biology of Canadian weeds. Centaurea
diffusa and C. maculosa. Can. J. Plant Sci. 54:687-701.

Wells, M. J., R. J. Poynton, A. A. Balsinhas, K. J. Musil, H. Joffe, E. van Hoepen and S. K. Abbott. 1986. The history of introduction of invasive alien plants to southern Africa. In: I. A. W. Macdonald, F. J. Kruger and A. A. Ferrar (ed.) The Ecology and Management of Biological Invasions in Southern Africa, Oxford University Press Cape Town, South Africa.

Wright, A.L., and R.G. Kelsey. 1997. Effects of spotted knapweed on cervid winterspring
range in Idaho. J. Range Manage. 50:487-496.

Zouhar, K. 2001. Centaurea maculosa. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: [ 2007, June 8].


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  • Roger Sheley


Materials and methods:

Bitteroot Valley Sites:
Two sites, Lando and Danny, in the Bitterroot Valley, MT were established in June and July 2003 to study integration of sheep grazing, biological control insects and broadcast native seeding to reduce the performance of spotted knapweed. Desirable species were then sown to determine if the light soil and vegetation disturbance caused by the sheep provided an increased number of safe sites for seed germination and survival.

Each site was divided into two whole plots for the biological control treatment. Three hundred adult Cyphocleonus achates, a biological control root feeding weevil for spotted knapweed, were released onto each biocontrol plot in late July - August in 2003, 2004 and 2005. Three 4.5 by 4.5 m grazing exclosures were constructed at random within each of the whole plots (biocontrol and no biocontrol) and used to test the sheep grazing effect on plant community characteristics. Approximately 300 ewes with lambs grazed both sites in July 2003. Native hay was cut in July 2003, and seeds from native forb species were collected throughout the summer and fall for subsequent application onto plots. Seed treatments (a no seeding control, perennial native grass species, native forb species, native grass and forb species mixed, and hay) were applied inside and outside the exclosures on 1 by 5 m plots in the second week of November 2003.

Baseline density and cover data of all species was collected from four randomly placed 0.2 by 0.5 m frames inside and outside each exclosure, at the time the exclosures were built in 2003 and before treatments were applied. Sheep utilization of spotted knapweed was sampled by clipping all plants within one 0.2 by 0.5 m frame placed inside and outside each exclosure after the grazing treatment was applied.

In 2004, the grazing treatments on the two sites in the Bitterroot Valley were modified. Site 1 could not be grazed because the cooperator was denied access to water. Site 2 was grazed by 12 rams from July through October.

Density and cover by species were sampled from one randomly placed 0.2 by 0.5 m frame from each of the five seeding treatments inside and outside each exclosure at both sites. The number of spotted knapweed flowering heads in each of the sample frames was also counted. Five soil samples were collected and pooled from inside and outside each of the exclosures, and assessed for nitrogen content and nitrogen mineralization. The grazing treatment was only applied and quantified at Site 2: sheep utilization of spotted knapweed and grass was sampled by clipping all plants within one 0.2 by 0.5 m frame placed inside and outside each exclosure.

Additional Seeding Treatment:
An additional seeding treatment was applied at both sites in November 2004. The seeding treatments were: no seeding, broadcast seeding of bluebunch wheatgrass, annual sunflower, and blue flax at a rate of 30, 10 and 10 lbs/acre, respectively, and, disc tillage of the soil to a depth of 5 cm with broadcast seeding of bluebunch wheatgrass, annual sunflower, and blue flax also at a rate of 30, 10 and 10 lbs/acre, respectively. The treatments were replicated three times. These were contained within the split, split plot design with biocontrol as the main effect and graze/no-graze as the secondary effect.

In 2005, management treatments were continued at the Bitterroot Valley sites; again, Site 1, Lando, could not be grazed because the cooperator was denied access to water. Site 2, Danny, was grazed by 12 rams from July through October. The additional seeding treatments applied in 2004 were sampled. The cover and density of all species and the cover of bare ground and litter were measured in randomly placed 0.2 by 0.5 m frames within each treatment plot.

In 2006, sampling of the Bitterroot Valley sites was concluded with assessments of cover and density of all species, bare ground and litter in random 0.2 by 0.5 meter frames within each treatment and sub-treatment plot. As in previous years, Lando (Site 1) was not grazed while Danny (Site 2) was grazed as outlined above.

Yellowstone Valley Site:
On the Ranch in the Yellowstone Valley an 80-acre pasture infested with spotted knapweed was sprayed in 1999 with 2,4-D to reduce spotted knapweed. Six 2 m2 exclosures were constructed to measure the effects of grazing on the plant community. Cattle grazing was deferred for two years after the herbicide application to allow grass recovery. The pasture was grazed by 100 ewes with lambs to reduce reestablishment of spotted knapweed 2001. In 2003, the pasture was first grazed by 150 cow-calf pairs in May until approximately 60% of the grass was utilized. This was followed by grazing by 50 ewes and their lambs. Predators were a problem at this site. Six hundred Cyphocleonus achates weevils were released on the pasture in July 2003.

In 2004, the grazing treatments were continued and an electric net fence was used to contain the sheep in the areas of the heaviest spotted knapweed infestation and to prevent predation of the sheep by foxes, coyotes, and wolves. Vegetation utilization was sampled from 1 m2 frames. The electric fence was effective in containing the sheep and excluding all predators with the exception of one grizzly bear.

In 2005, the Melin family developed solutions to the predator problems they were having with their sheep flock. The construction of a bear, lion, and wolf proof pen has provided a safe over-night location for the flock. Use of the net electric fence has allowed them to contain the flock on grazing sites targeted for weed management during the day. Grazing management on the 80-acre pasture continued with cattle grazing the pasture in the spring and periodically during the summer. The electric sheep pen was placed around each exclosure and sheep grazed the plots in July. No data were available from this site for any quantitative analysis to be performed.

Research results and discussion:

This research and demonstration aimed to show how management actions affect species abundance, and our ability to change a plant community from being dominated by invasive forb species to being dominated by more desirable species. Understanding how disturbance (in terms of grazing and tilling), and native species abundance (from seeding), can be used to reduce invasive species helps landowners and managers design and predict the outcome in integrated weed management techniques. This project also demonstrates how resources available on ranches can be used to follow ecological principals and manage invasive species and improve grazing productivity.

Bitterroot Valley:
Grazing Treatment:
Grazing by sheep only occurred in each year at the Danny site. Grazing did significantly reduce flowering spotted knapweed density by 2.6-fold in the grazed exclosures versus the no-grazed control exclosures in 2004 (Figure 1). The difference between the grazed plots and no-grazed plots in 2006 is further enhanced with a 6-fold decrease in flowering spotted knapweed in the grazed plots (Figure 1). It should be noted there was an overall decrease (3-fold) in the density of flowering spotted knapweed in the control plots between 2004 and 2006 (Figure 1) and there was not a significant change in total richness during the same time period (≈ 2.5 species/m2). This suggests that spotted knapweed was declining naturally at this site at this time, possibly due to climate or a change in grazing ungulates. The low species richness which stayed the same over the ample period suggests a stable system, albeit with low richness.

At the Lando site which was only grazed by sheep in 2003, the overall density of flowering spotted knapweed also decreased 2.2-fold from 2004 to 2006 for all sampled plots (Figure 2), but unlike the Danny site, the Lando site showed a slight but statistically significant increase in total richness in 2006; with a mean richness of 2.5 species/m2 in 2004 compared to 2.8 species/m2 in 2006. This again suggest unsuitable habitat for spotted knapweed at this time. The Lando site was not grazed since 2003 and there was no significant statistical difference between the grazed or no-grazed plots in 2003 when sampled in 2004 or 2006 (data not shown).

Biocontrol Treatment:
The biocontrol treatment with no other treatment applied significantly increased the flowering spotted knapweed numbers at the Danny site during 2004 and to a lesser degree in 2006 (Figure 3). However when biocontrol plots were also grazed, flowering spotted knapweed densities decreased compared to control plots, although not to the levels seen with grazing alone (Figure 3). Biocontrol plots showed significant increases in total spotted knapweed from 2003, the year weevils were initially released, to sampling years 2004 and 2006 (Table 1). There was no significant year difference in total density of spotted knapweed between 2004 and 2006 (≈ 50 plants/m2). However, densities were significantly lower in the grazed plots and similar in the control and grazed/biocontrol plots with the biocontrol plots having the highest density of spotted knapweed (Table 1).

At the Lando site, biocontrol had no effect on total spotted knapweed density (≈ 79 plants/m2 in all treatments), flowering plants density (≈ 43 plants/m2) and juvenile rosette density (≈ 36 plants/m2). Unfortunately, the density of C. achates was not recorded in any year.

Seeding Treatment:
It was anticipated that sheep grazing would sufficiently disturb the soil and vegetation to increase site availability for establishment of sown desirable species as part of the five seeding treatments imposed in 2003. The only sub-treatment to show a statistical difference was the hay plots. At both the Lando and Danny sites in 2004 and 2006, the hay plots had lower spotted knapweed densities (Table 2) and higher litter percentages than the control (Table 2) or other seeding treatments plots (Table 2). Most likely spotted knapweed is unable to establish itself in the hay plots due to the high litter caused by the hay treatment. It is possible due to seeding timing or seasonal rainfall the seeding treatments were ineffective and the desirable species were unable to colonize. Correspondingly, bareground was less in the hay plots, significantly so at the Lando site (Table 2). There were no differences in the densities of native or non-native forbs and grasses between the seeding treatments at either site. The densities of non-native forbs and grasses were decreased in the hay treated plots (data not shown).

Native Grass and Forb Species:
As expected, where grazing only was imposed at the Danny site, the amount of bareground was significantly higher, but the percentage of bareground decreased in grazed plots with biocontrol (Table 3). Interestingly, the biocontrol plots at both the Danny and Lando sites showed an increased number of native forb species than the plots without biocontrol (Table 4), albeit the means are less than one. This suggests that although the amount of spotted knapweed is increasing in the biocontrol plots, there are new safe sites opening up for native forbs to establish and it is perhaps only a matter of time before the native forbs are able to out compete spotted knapweed establishment. Native grass species richness was similar at both Stevensville sites between control plots and biocontrol plots (data not shown).

Overall at both the Lando and Danny sites, native forb and grass species richness increased from 2004 to 2006 (Table 5), but was still low. Non-native forb richness at the Danny site and total non-native grass species at the Lando site decreased (Table 5). However, there was a significant increase in the density of the non-native cheatgrass during the same time period at both the Stevensville sites (Table 6). Most of the increase in cheatgrass at the Danny site is attributed to grazed plots with biocontrol (Table 7). Biocontrol had no affect on cheatgrass density at the Lando site (data not shown).

Rosette Density:
The rosette demographic of spotted knapweed provides an indication of the future population of the weed. Rosettes increased in numbers at both the Lando and Danny sites between 2004 and 2006 (Figure 4). At the Danny site, this increase in rosettes was regardless of grazing, biocontrol or seeding treatments (data not shown). The general increase in juvenile plants possibly suggests more favorable growing conditions in 2006 than in 2004, although this contrasts the pattern of flowering plants. Juvenile spotted knapweed numbers were not affected by the biocontrol treatment at Lando (data not shown), but densities were different in the seeding treatment with significant increase between years (Table 8). As expected, the hay plots showed a significant reduction in the number of rosettes.

Nutrient Status:
Nutrient status was assessed at the Danny site in 2004 within exclosures and in grazed plots. There was no significant effect of grazing on soil nitrogen dynamics. Total available nitrogen at that time (NO3 + NH4) tended to be lower, and potentially mineralizable nitrogen (PMN) tended to be higher, in the grazed plots compared to the plots excluded from grazing at the Danny site after two seasons of grazing (Table 9). These trends suggest that available nitrogen is being used more efficiently and that microbial production of available nitrogen is greater where there is grazing compared to where grazing is excluded. This may indicates a more active nitrogen cycle where sheep graze compared to where there is no grazing. The nitrogen cycle is a critical ecosystem function that affects productivity. There are many unanswered questions concerning invasive species, management, and the nitrogen cycle that may provide insight into invasions and their management.

Additional Seeding Treatment:
The additional disturbance and seeding study was initiated in 2004 because the disturbance of sheep and their grazing did not allow for successful establishment of native seeded species. Thus, establishment of native species was lower than desired so using more invasive methods needed to be assessed. Therefore, we assessed shallow tillage with broadcast seeding, broadcast seeding alone plus a control of no seeding. The species in the seeding mixture were bluebunch wheatgrass at 30 lbs per acre, annual sunflower at 10 lbs per acre, and blue flax at 10 lbs per acre. Of all species established, bluebunch density increased from 2005 to 2006 at both sites, flax densities remained low in both years, and unsurprisingly annual sunflower was only observed in the first year at very low levels (Table 10).

Seeding treatment had a significant effect on spotted knapweed plant density at both sites in 2005, but there was no significant difference in 2006 (Table 11). Bluebunch wheatgrass densities were significantly different at both sites in 2005, and Lando in 2006 with highest densities in the tillage and seed treatment (Table 11). This result indicates that seeding alone will not improve establishment of desired native species, and a pretty intense disturbance such as shallow tilling is needed to create safe sites for establishment. Cheatgrass density did not differ statistically significantly between the different treatments (data not shown) which is encouraging. It is anticipated that in the long-term, the establishment of a long-lived perennial bunchgrass combined with the reduction in performance of spotted knapweed by sheep grazing and aggressive seeding will change the plant community to a more desirable native bunch grass community.

Yellowstone Valley:
Drs. Jacobs and Rew met with the Melin family in early summer 2006. Grazing levels of both cattle and sheep were high. Visual inspections of the site lead Dr. Jacobs to believe that spotted knapweed densities had declined. Examination of roots showed the establishment of the C. achates weevil.

The exclosures had noticeably higher levels of plant biomass. Therefore, spotted knapweed plants made up a smaller proportion of the total biomass. Outside of the exclosures grazing intensity was sufficiently high that while spotted knapweed plants may have been declining in density, the native and desirable species did not appear to be recovering. This suggests that lower grazing intensity would help native and more desirable vegetation to establish and become more prolific. However, the Melin Family did not consider it an economically viable option to reduce their stocking levels.

Research conclusions:

Management and a reduction in the abundance of established spotted knapweed and other invasive species populations (e.g. cheatgrass) should be considered as a longer term objective. There are no “silver bullets” to invasive species management; instead, the best weed management is that of “many little hammers”, which suggests the integration of a range of management treatments will help to reduce the target populations of invasive species to a more desirable and negatively impacting level.

The experiments established by Drs. Jacobs and Sheley along with their collaborators, demonstrates the potential advantages of sheep grazing and seeding of native species combined with soil disturbance, and the difficulties of establishing sufficient population levels of biocontrol agents. The results presented in this report demonstrate that sheep grazing is an effective treatment for the control of spotted knapweed. However, grazing alone was not sufficient to induce the establishment of desirable species; in fact, grazing appeared to open safe sites for germination of more invasive plants. Shallow tillage followed by seeding of native species is a promising treatment in inducing succession toward favorable species. Although, our results suggest that evaluation of different seeding densities, a larger number of species and different seeding times would be beneficial to direct future extension recommendations.

The results and practical implications of these findings have been presented in numerous forums by Drs. Jacobs and Sheley and their associates during the course of this project. Please refer to Publications and Outreach section below.

Participation Summary

Research Outcomes

No research outcomes

Education and Outreach

Participation Summary:

Education and outreach methods and analyses:

Sheley, R.L., J.S. Jacobs, and T.J. Svejcar. 2005. Integrating disturbance and colonization during revegetation of invasive weed-dominated grasslands. Weed Science. 53:307-314.

Jacobs, J.S. and R.L. Sheley. In revision. Integrated management of leafy spurge. J. Range Manage. 8 March 2004.

Sheley, R.L., J.S. Jacobs, and M.F. Carpinelli. Submitted. Rehabilitating weed resistant plant communities using niche-differentiated non-native species. J. Range Manage. 16 Dec. 2003.

Jacobs, J.S., S.R. Windslow, and M.L. Pokorny. Submitted. The Effect of Five Pre-emergent Herbicides on the Emergence and Establishment of Seven Native Wildflowers. Native Plants Journal. 1 December 2005.

Jacobs, J.S. S. E. Sing, and J. M. Martin. Submitted. Interactions of herbivory and competition on invasive weed performance: effects of Cyphocleonus achates and grass-seeding treatments on Centaurea maculosa. Environmental Entomology. 23 December 2005.

Windslow, S.R. and J.S. Jacobs. The effect of five pre-emergent herbicides on wildflowers. Plant Material Center Today. Technical Report. April 2005.

Jacobs, J.S. and A. Knudsen. 2005. Restoring perennial grasses on a leafy spurge infested pasture. Society for Range Management 58th Annual Meeting. Fort Worth, TX.

Pokorny, M.L., J.S. Jacobs, P. Tryon, G. Bennett, and A. Soukkala. 2005. Using an ecological framework to manage invasive species. Society for Range Management 58th Annual Meeting. Fort Worth, TX.

Goodwin, K and J. Jacobs. 2005. Montana Weed Prevention Areas: Partnerships for Range Protection. Cal-IPC Symposium Proceedings.

Jacobs, J.S. and R.L. Sheley. 2003. Integrating 2,4-D and sheep grazing to restore native plants to spotted knapweed-infested rangeland. In Assembling the pieces; restoration, design and landscape ecology. The Society for Ecological Restoration International. Austin, Texas. p. 30.

Jacobs, J.S. Cheatgrass Management, an ecological perspective. In: Proceedings Pest Management Training, October 2003 MSU Extension Service.

Sheley, R.L., J.S. Jacobs, and J.M. Martin. 2004. Integrating 2,4-D and sheep grazing to rehabilitate spotted knapweed infested rangeland. J. Range Manage. 51:371-375.

Jacobs, J.S. and M.L. Pokorny. 2004. Restoring perennial grasses in a spotted knapweed infested rangeland: and eight-year look. Proceedings of the 16th International Conference, Society for Ecological Restoration, August 24-26, 2004, Victoria, Canada. 4 p.

Pokorny, M.L. and J.S. Jacobs. 2004. Going over the edge: Case studies using ecology to restore invaded lands. Proceedings of the 16th International Conference, Society for Ecological Restoration, August 24-26, 2004, Victoria, Canada.

Jacobs, J.S. 2004. Combining a parasite and a competitor to reduce Centaurea maculosa population density. In: Lessons of Lewis and Clark: Ecological Exploration of Inhabited Landscapes. The Ecological Society of America. Portland OR. p. 243-244.

Jacobs, J.S. and M Pokorny. A burning reality; can Linaria dalmatica be controlled after wildfire. Federal Fire Rehabilitation Symposium. Society for Range Management Annual Meeting. Salt Lake City. 29 January 2004.

Jacobs, J.S. and R.L. Sheley. Integrated Management of leafy spurge. TEAM Leafy Spurge Symposium. Society for Range Management Annual Meeting. Salt Lake City. 27 January 2004. Invited.

Jacobs, J.S., 2004 Weevils and wheatgrass winning the war with knapweed. Montana Weed Times. October.

Presentations and Workshops and Instructional Activities:
Jacobs, J.S. Ecologically based noxious weed management. Montana State Fish Wildlife and Parks Annual Meeting, Chico, MT. 25 attended.

Jacobs, J.S. Economic and ecological impacts of noxious weeds. Realtor Training, Sheridan MT, 18 November 2005. 15 Attended.

Jacobs, J.S. Integrated weed management in Montana, and how weed management areas work. A meeting to develop cooperative weed management in Saskatchewan. Mankota SK. 19 October 2005. 15 attended.

Jacobs, J.S. and Alan Knudsen. Ecologically based integrated management of leafy spurge. Wyoming managers field tour. 13 September 2005. 14 attended.

Jacobs, J.S. Weevils and Wheatgrass: Jacobs, J.S. and A. Knudsen, Ecologically based weed management. Western Montana Weed Tour. 21 July 2005. 50 Attended.

Jacobs, J.S. 2005. Natural Resources and Conservation Service Noxious Weed Management Training. St Mary, Great Falls, Glasgow, Bozeman, Miles City. May, June, July. 40 attended each, invited.

Jacobs, J.S. 2005. Restoration of Weed Infested Sites and Annual Grass Management. Noxious weed Management Short Course. Western Society of Weed Science. Pray, MT. 28 April. 41 attended. invited

Jacobs, J.S. 2005. Ecology and Management of Dalmatian and Yellow Toadflax. Noxious weed Management Short Course. Western Society of Weed Science. Pray, MT. 27 April. 41. invited.

Jacobs, J.S. 2005. Noxious Weed Identification. Noxious weed Management Short Course. Western Society of Weed Science. Pray, MT. 26 April. 41 attended

Jacobs J.S. 2005. Managing Noxious Weeds on Pastures. Pasture Management Workshop. DNRC, Bozeman. 13 April. 20 attended. Invited

Jacobs, J.S. 2005. Integrated Weed Management Strategies: How Does Grazing Fit In? Sheep, Goats, Weeds, and Wildlife Workshop. Missoula, MT. 29 March. 100 Attended.

Jacobs, J.S. 2005. Drought, Heat, and herbicide Management of Noxious Weeds. Montana Weed Coordinators Training. Dillon, MT. 10 March. invited. 50 Attended.

Jacobs, J.S. 2005. Noxious weed management on small acreage. 19 February. Wild West Winter Fest. Bozeman, MT. 10 attended

Integrated Management of Large Populations of Spotted Knapweed. Montana Weed Control Association Annual Conference. Helena, MT. 26 January 2005. 50 attended. invited.

Jacobs, J.S. 2005. Planning Noxious Weed Management. Crop Pest Management. 6 January, 0.5 hr. Bozeman, MT. 35 attended.

Jacobs, J.S. and M.L. Pokorny. Applying ecological concepts and technology developed through research to wildland management and commercial restoration. Bitterroot Restoration Incorporated and The Teller Wildlife Refuge. 16 August 2004. Corvallis, MT.

Jacobs, J.S. and A. Knudsen. Integrated management of leafy spurge. Missoula County Restoration Demonstration Field Tour. 27 July 2004. Lolo, MT. 20 attended.

Jacobs, J. S. and M. L. Pokorny. Ecologically Based Management of Dalmatian Toadflax. After the Fire; Bucksnort Field Tour. 24 June 2004. East Helena, MT. Invited 50 attended.

Jacobs, J.S. 2004. Managing Noxious Weeds. Montana Outdoor Science School. 12 June 2004. Bozeman, MT. 20 attended. invited

Jacobs. J.S. 2004. Canada thistle control in shelterbelts and rangeland. McCone Conservation District/Plant Materials Center Grass Demonstration Plot Tour. Circle MT. 3 June. Invited. 20 attended. Extension Pesticide Training.

Jacobs, J.S. 2004. Ecologically based noxious weed management. Headwaters RC&D Range Weed Committee Meeting. Butte MT. 20 May. Invited. 15 Attended.

Jacobs, J.S. 2004. Integrated Weed Management. FY 2004 NRM EPMT Training. Mammoth, WY. 11 May. 10 Attended. Invited.

Jacobs, J.S. 2004. Effective Weed Management. FY 2004 NRM EPMT Training. Mammoth, WY. 11 May. 10 Attended. Invited.

Jacobs, J.S. 2004. Restoration of Weed Infested Sites. Noxious weed Management Short Course. Western Society of Weed Science. Pray, MT. 28 April. 43 attended

Jacobs, J.S. 2004. Ecology and Management of Dalmatian and Yellow Toadflax. Noxious weed Management Short Course. Western Society of Weed Science. Pray, MT. 28 April. 43 attended

Jacobs, J.S. 2004. Noxious Weed Identification. Noxious weed Management Short Course. Western Society of Weed Science. Pray, MT. 27 April. 43 attended

Jacobs, J.S. 2004. Top Ten Ecological Concepts of Integrated Weed Management. Noxious weed Management Short Course. Western Society of Weed Science. Pray, MT. 27 April. 43 attended

Jacobs, J.S. 2004. Managing Noxious Weeds on Pastures. Pasture Management Workshop. DNRC, Bozeman. 21 April, 19 May, and 6 October. 30, 20, and 24 attended. Invited.

Jacobs, J.S. 2004. Weed Management Plan Evaluation. Master Gardner Weed Management Course. Missoula, MT. 1 May. 35 attended

Jacobs, J.S. 2004. Grazing Management Strategies for Noxious Weeds. Master Gardner Weed Management Course. Missoula, MT. 25 March. 35 attended.

Jacobs, J.S. 2004. A Burning Reality: Should we control Dalmatian Toadflax After Wildfire. MSU-LRES Weeds Group Lunch Bunch Seminar. 23 March. 20 attended.

Pokorny, M.L. and J.S. Jacobs. 2004. What is Ecologically-based Invasive Species Management? Third Annual Agricultural Conference and Expo. University of Montana-Western. Dillon, MT. 9 January. 25 attended. invited

Jacobs, J.S. Cheatgrass Management; an ecological perspective. Ravalli County pesticide application recertification training. 7 October 2003. 50 attended. invited

Jacobs, J.S. Revegetation Strategies. Ravalli County pesticide application recertification training. 7 October 2003. 50 attended. invited

Jacobs, J. S. Grazing strategies on noxious weeds. Missoula County pesticide applicator recertification training. 11 September 2003. 50 attended. Invited.

Education and Outreach Outcomes

Recommendations for education and outreach:

Areas needing additional study

Broadcast seeding with shallow tillage did improve establishment of native species over disturbance caused by sheep, or no disturbance. Further experimentation evaluating different seeding densities, a larger number of species and different seeding times would be beneficial to direct further extension recommendations.

Studies of invasive species including spotted knapweed, cheatgrass, yellow toadflax and tansy ragwort have shown that not all populations of these invasive species increase consistently (Rew, unpublished). The same patch may increase, be relatively stable or decline overtime. To obtain a better understanding of such population dynamics fixed or permanent quadrants should be used for assessments. We advise that future projects should be encouraged to use permanently marked quadrants.

C. achates did not significantly reduce spotted knapweed densities in most of the plots. This may be due to poor establishment of the weevil. Jacobs (2004) and Corn et al. (2006) found that several years may be required to achieve sufficient densities of C. achates in the roots of spotted knapweed. We would therefore recommend extended study periods of more than 3 years to make conclusive statements as to the value of this weevil in our region.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.