Final Report for SW06-075

Project Type: Research and Education
Funds awarded in 2006: $62,600.00
Projected End Date: 12/31/2010
Region: Western
State: Montana
Principal Investigator:
Tracy Brewer
Park County Extension - Montana State University
Co-Investigators:
Dr. Tracy Mosley
Montana State University Extension
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Project Information

Abstract:

Spotted knapweed (Centaurea stoebe), an aggressive competitor and ecologic threat, produces 25-35 flowers/head, 60 heads/plant and 5,000-40,000 seeds/meter squared annually. Prescribed sheep grazing, a tool used to control spotted knapweed, can offsets high costs of control and environmental concerns surrounding herbicides. However, spotted knapweed forms new flowers after prescribed sheep grazing is applied during the bolting or flowering stage. It is unknown if these new flowers produce viable seeds by the end of the growing season. The purpose of this two-year study was to determine the appropriate timing(s) or combination(s) of timings of defoliation on spotted knapweed to reduce viable seed production.

Project Objectives:

Objective 1: Evaluate the effects of timing of spotted knapweed defoliation on: a) the number of buds/flowers present, b) the percent viability of filled seeds and c) the total number of viable seeds produced to determine the best timing of spotted knapweed defoliation to minimize viable seed incorporation into the seedbank annually.

Objective 2: Combine results of this study with past research and existing grazing prescription protocols to refine the technique of using sheep grazing to control spotted knapweed.

Objective 3: Educate ranchers, other landowners, livestock operators, county extension personnel, county weed district personnel, state and federal agency personnel, Montana State University researchers and concerned citizens about how properly timed sheep grazing to control spotted knapweed can reduce the amount of viable seed applied to the seedbank in a single growing season and can enhance the ecological integrity of the land.

Introduction:

Spotted knapweed infestations threaten the ecological sustainability of western rangelands and the economic sustainability of western ranches and rural communities. Spotted knapweed is an extremely aggressive competitor that is capable of forming large monocultures (Tyser and Key 1988; Lacey et al. 1990), reducing biodiversity (Tyser and Key 1988) and available forage for livestock and wildlife (Watson and Renney 1974), and increasing surface water runoff, soil erosion and sediment yield in streams (Lacey et al. 1989; Lacey et al. 1990). Spotted knapweed produces 25-35 flowers per head (Sheley et al. 1999) and can produce 5,000-40,000 seeds per meter squared each year (Shirman 1981). Buds form on spotted knapweed plants in June and flowering generally occurs from July through September, with mature seeds being formed by mid-August (Sheley et al. 1999). Very few seeds overwinter on spotted knapweed plants and most are shed upon maturity (Hirsch and Leitch 1996; Sheley et al. 1999), contributing extreme numbers of seeds into the seedbank annually. Spotted knapweed seeds are also very durable and capable of surviving in the soil for up to eight years (Davis et al. 1993).

Spotted knapweed is found in all 11 western states, currently exists in every Montana, Idaho, Wyoming, and Washington county (Sheley et al. 1998) and covers 3.8 million acres of rangeland, pastureland, cropland, forests and wildlands critical for agricultural production in Montana (MWSSC 2005). Knapweed causes more than $42 million in losses annually to Montana’s economy in direct and indirect costs, including a $36 million loss associated with grazing lands and livestock production, a $2.6 million loss in wildlife-associated benefits such as wildlife habitat, hunting, photography, and other wildlife-related recreation, and a $3.4 million loss related to soil and water conservation (Hirsch and Leitch 1994). Money lost to knapweed in Montana could support 518 full time jobs in the state annually (MWSSC 2005).

The potential negative impacts of spotted knapweed on ecological processes on rangelands that support livestock and wildlife and on farm, ranch and rural economies are great. It is estimated that the spread rate of spotted knapweed is 10% per year, and that ground control for weed management costs landowners, ranchers and agencies a minimum of $25.00 per acre, excluding labor and equipment costs (MWSSC 2005). Additionally, for long-term control, annual reapplication of herbicides is necessary until the seedbank is depleted (Sheley et al. 1999). Ecologically compatible and economically feasible control methods are critically needed to reduce the devastating impacts of spotted knapweed.

Spotted knapweed control has typically involved integrated management including herbicides, biological control, or both. The high cost of herbicide application makes it unattractive to ranchers with large acreages of spotted knapweed invasion on their rangeland and makes it economically unfeasible (Griffith and Lacey 1991). While ground application of herbicides costs a minimum of $25.00 per acre, recent estimates of the cost of weed control with prescribed grazing have been much lower. For example, a rancher from southeastern Montana that trucks his sheep to southwestern Montana to graze spotted knapweed on other private land incurs estimated costs, including herding, camp tending, trucking and increased death rates, of $3.81 per acre (Kott 2005). Additionally, prescribed grazing does not possess the perceived potentially negative environmental effects of herbicides. In response to the high costs and environmental concerns surrounding herbicides, more cattle ranchers have begun to explore the efficacy of prescriptive sheep grazing on spotted knapweed invasions, and researchers have recently begun investigating appropriate grazing techniques for maximum spotted knapweed control (Olson et al. 1997; Olson and Wallander 2001; Hale 2002; Thrift et al. 2008).

Previous research indicates that sheep will readily consume spotted knapweed even when other desirable forage is available (Olson and Wallander 2001; Hale 2002; Thrift et al. 2008), spotted knapweed is a nutritious forage source for livestock (Kelsey and Mihalovich 1987; Olson and Wallander 2001; Hale 2002), and defoliation can reduce the plant’s ability to produce flowers and seeds (Olson et al. 1997) and seed germination rates (Watson and Renney 1974). Additional benefits of prescriptive sheep grazing for spotted knapweed control exist. Besides the environmental and economic benefits of substituting sheep grazing for herbicide application, the incorporation of sheep grazing for spotted knapweed control into existing cattle ranching operations increases the number of food and fiber products produced per acre, promotes enterprise diversification and adds another source of income to the ranch operation. Ultimately these benefits will contribute to the enhanced economic and environmental sustainability of western ranching operations where spotted knapweed is a threat. However, effective landscape-scale grazing prescriptions, including the most effective timing of defoliation to reduce the amount of viable seed incorporated into the seedbank annually, must exist in order for sheep grazing for spotted knapweed control to positively contribute to the ecological and economic stability of western cattle ranches. One question that remains unanswered is how early or late in the growing season spotted knapweed defoliation needs to occur to reduce the production of viable seed. Understanding how different timings and combinations of multiple timings of defoliation of spotted knapweed impacts seed viability can help decrease the amount of seed added to the seedbank annually.

Cooperators

Click linked name(s) to expand
  • Chase Hibbard
  • David Mannix
  • Lee Rinehart
  • Jason Smith
  • Jim Stone

Research

Materials and methods:

This two-year field study was located on foothill rangeland on the Mannix Brothers Ranch, in western Montana. Each year, 80 individual spotted knapweed plants, located on a moderately infested site, with average stature and of similar size were chosen, tagged for identification and excluded from large ungulate grazing with a welded wire panel exclosure. Hand-clipped treatments were applied to the spotted knapweed plants to emulate observed sheep grazing behavior (n=10 plants per treatment). Treatments include:

1) 45% relative utilization of above-ground biomass when plants were in the bolting stage,

2) 100% of buds removed at late bud/early flowering stage,

3) 100% of flowers removed at full flower,

4) Treatment 1 + Treatment 2,

5) Treatment 1 + Treatment 3,

6) Treatment 2 + Treatment 3,

7) Treatment 1 + Treatment 2 + Treatment 3, and

8) unclipped control.

Response variables in this study included:

1) number of buds/flowers per plant,

2) number of doughy, intermediate and mature seeds per plant,

3) total number of seeds per plant,

4) percent viability of doughy, intermediate and mature seeds,

5) number of viable doughy, intermediate and mature seeds per plant, and

6) total number of viable seeds per plant.

Spotted knapweed plant response was evaluated whenever each treatment’s plants reached senescence (mid-August through September), when seeds were developed to their fullest possible extent but while seedhead bracts remained closed, and before seed dispersal (Watson and Renney 1974; Schirman 1981).

Originally, germination rate of spotted knapweed seeds was included as a response variable. During the laboratory analysis process in Year 1, we made a decision to eliminate the germination test on the spotted knapweed seeds. The reasons for this were two-fold. First, in many treatments, plants did not produce enough seeds to complete a statistically sound test for both viability and germination, and secondly, from previous experience we know that there is an extremely high potential for seeds to mold during the germination process, which adversely affects germination. For these reasons, we restricted our laboratory analyses to spotted knapweed seed numbers and viability.

The experimental design for this study was completely randomized. Treatments were arranged in an 8 x 2 factorial arrangement, with eight timings/combinations of timings of defoliation and two years. The statistical model included year, timing of defoliation and year and timing interaction. Individual plants were the experimental units. Analysis of covariance (ANCOVA) procedures in SAS (SAS Institute 2004) was used to determine differences in plant response between treatments. Percent canopy cover of spotted knapweed, lupine and perennial graminoids; percent of buds/flowers with evidence of gall fly damage; and initial plant height were used as covariables in the analyses. Fisher’s Protected LSD Test was used to compare treatment means (Steel and Torrie 1980), and differences were considered significant at P ? 0.05.

Research results and discussion:

Spotted knapweed produced new buds and flowers after plants were clipped once, twice or three times during summer. However, all seven clipping treatments reduced the number of buds/flowerheads present at the end of the growing season compared with no clipping (P < 0.01). Clipped plants produced 73-98% fewer buds/flowerheads than unclipped plants (Table 1). All defoliation treatments in our study reduced the number of viable seeds produced by spotted knapweed. This finding helps explain why a previous study in southwestern Montana reported that more viable spotted knapweed seeds were recovered from seed bank soil cores from ungrazed areas than from areas that were grazed by sheep in mid-June, July and early September (Olson et al. 1997).

All seven clipping treatments also reduced seed production by spotted knapweed. The number of doughy seeds, intermediate seeds, mature seeds and total seeds were all reduced by clipping (P < 0.01). Clipping in June during the bolting stage reduced the total number of seeds 75-81%, whereas clipping at all other times or combinations of timings reduced the total number of seeds produced 98-100% (Table 2).

No doughy seeds were viable throughout the study (Table 3). Clipping in June during the bolting stage reduced percent viability of intermediate seeds 57% (P < 0.01), whereas clipping at all other timings or combinations of timings reduced percent viability of intermediate seeds 99% compared with no clipping (P < 0.01; Table 3). All seven clipping treatments also reduced the percent viability of mature seeds. Clipping in June during the bolting stage reduced percent viability of mature seeds 23-58%, whereas clipping at all other timings or combinations of timings reduced percent viability of mature seeds 58-99.6% (Table 3). Intermediate seeds and mature seeds from unclipped spotted knapweed plants in our study averaged 35% and 89% viability, respectively, while the weighted average of intermediate and mature seed viability from unclipped plants was 69%. This result compares favorably with previous reports of 60-82% viability of current years’ seeds (Jacobs and Sheley 1998).

The numbers of viable intermediate, mature and total seeds were all reduced by clipping (P < 0.01). Clipping in June during the bolting stage reduced the total number of viable seeds nearly 90% compared with no clipping (Table 4). Clipping in July during the late-bud/early-flower stage, clipping in August during the full-flower stage or clipping at any combination of timings reduced the total number of viable seeds almost 100% compared with no clipping (Table 4). Our results indicate that viable seed production of spotted knapweed is most effectively suppressed by defoliation during either the late-bud/early-flower stage or full-flower stage.

Our findings of the appropriate time for defoliation align favorably with results from studies of sheep foraging behavior when sheep prescriptively graze within spotted knapweed infestations. Sheep readily consume the buds and flowerheads of spotted knapweed, including during late summer (Olson and Wallander 2001). In western Montana, sheep prescriptively grazed on a landscape scale in July or August commonly consume >90% of spotted knapweed buds/flowerheads (J. Mosley, unpublished data). Sheep in moderate to heavy spotted knapweed infestations typically consume less graminoids and more spotted knapweed when prescribed sheep grazing occurs in the late-bud/early-flower stage rather than the bolting stage (Thrift et al. 2008). The late-bud/early-flower stage and full-flower stage of spotted knapweed usually occur after rangeland graminoids have set seed and become less palatable and less vulnerable to defoliation (Olson et al. 1997; Thrift et al. 2008), but while the forage volume and nutritive value of spotted knapweed remain high (Olson and Wallander 2001; Thrift et al. 2008). It should be noted that 22% of mature spotted knapweed seeds remain viable after passing through the digestive system of a sheep (Wallander et al. 1995). However, mature spotted knapweed seeds are not formed until post-flowering in mid-August (Watson and Renney 1974); therefore, if grazing sheep ingest spotted knapweed buds and flowerheads before the full-flower stage, sheep will not ingest nor excrete viable seeds, nor collect viable seeds in their wool.

Clipping effects in our study also compare favorably with previous studies of mowing treatments within spotted knapweed infestations. Mowing during the full-flower stage reduced spotted knapweed seed germination 71% in western Canada (Watson and Renney 1974). In southwestern Montana, Rinella et al. (2001) reported that three years of mowing during the late-flowering/seedset stage (late August) reduced spotted knapweed canopy cover 83-85% and reduced the density of adult spotted knapweed plants 65-88%. Furthermore, mowing once each year during the late-flowering/seedset stage suppressed spotted knapweed as much as mowing two, three or ten times per summer. The late-flowering/seedset stage recommended for mowing by Rinella et al. (2001) is a slightly more advanced phenological stage than the late-bud/early-flower stage or full-flower stage that we found optimal for suppressing viable seed production of spotted knapweed. Rinella et al. (2001) did not evaluate mowing only once during either the late-bud/early-flower stage or the full-flower stage, but we suspect that mowing during these phenological stages would suppress spotted knapweed as much or more than mowing during the late-flowering/seedset stage. Spotted knapweed plants in the late-bud/early flower stage or the full-flower stage have greater numbers of actively growing meristems than plants in more advanced phenological stages. Following defoliation the active meristems act as sinks and draw more photosynthate (Briske and Richards 1995). Plants defoliated late in the growing season may have insufficient time before dormancy to replenish the photosynthate that was allocated to the active meristems immediately following defoliation, resulting in weakened plants entering dormancy with fewer carbon reserves (Dahl 1986).

Our clipping treatments reduced spotted knapweed seed production more in 2007 than 2006. It is well established that spotted knapweed produces fewer seeds in drier years (Schirman 1981; Sheley et al. 1998), and it appears that our clipping treatments more effectively reduced spotted knapweed seed production when combined with less crop-year precipitation (beginning September 1, 2006 and ending June 30, 2007) in 2007. It is noteworthy that although crop-year precipitation was less in 2007 than 2006, precipitation in both crop-years exceeded the 30-year average (22% and 13% above average in 2006 and 2007, respectively; WRCC 2008). We suspect that defoliation of spotted knapweed in summer would likely reduce spotted knapweed seed production even further during drier years than did clipping during the relatively wet years of our study.

Literature Cited

Briske, D. D., and J. H. Richards. 1995. Plant responses to defoliation: a physiological, morphological and demographic evaluation. In: D. J. Bedunah and R. E. Sosebee [EDS.]. Wildland plants: physiological ecology and developmental morphology. Denver, CO, USA: Society for Range Management. p. 635-710.

Dahl, B. E. 1986. Using range resources for best ranching success. Proceedings of the 1986 International Ranchers Roundup, Kerrville, TX, USA. College Station, TX, USA: Texas A&M University. p. 147-156.

Davis, E. S., P. K. Fay, T. K. Chicoine, and C. A. Lacey. 1993. Persistence of spotted knapweed (Centaurea maculosa) seed in soil. Weed Science 41:57-61.

Griffith, D., and J.R. Lacey. 1991. Economic evaluation of spotted knapweed [Centuarea maculosa] control using picloram. Journal of Range Management 44:43-47.

Hale, M. 2002. Developing prescription grazing guidelines for controlling spotted knapweed with sheep [thesis]. Moscow, ID: University of Idaho. 66 p.

Hirsch, S.A., and J.A. Leitch. 1996. The impact of knapweed on Montana’s economy. Fargo, ND: North Dakota State University Agricultural Experiment Station, Agricultural Economics Report 355. 43 p.

Jacobs, J. S., and R. L. Sheley. 1998. Observation: life history of spotted knapweed. Journal of Range Management 51:665-673,

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

Kott, R. 2005. Personal communication. Montana Sheep Institute Coordinator, Montana State University-Bozeman.

Lacey, J., P. Husby, and G. Handl. 1990. Observations on spotted and diffuse knapweed invasion into ungrazed bunchgrass communities in western Montana. Rangelands 12:30-32.

Lacey, J.R., C.B. Marlow, and J.R. Lane. 1989. Influence of spotted knapweed (Centaurea maculosa) on surface water runoff and sediment yield. Weed Technology 3:627-631.

[MWSSC] Montana Weed Summit Steering Committee. 2005. The Montana weed management plan, revised. Helena, MT: Montana Department of Agriculture. 88 p.

Olson, B.E., and R.T. Wallander. 2001. Sheep grazing spotted knapweed and Idaho fescue. Journal of Range Management 54:25-30.

Olson, B.E., R.T. Wallander, and J.R. Lacey. 1997. Effects of sheep grazing on a spotted knapweed-infested Idaho fescue community. Journal of Range Management 50:386-390.

Rinella, M. J., J. S. Jacobs, R. L. Sheley, and J. J. Borkowski. 2001. Spotted knapweed response to season and frequency of mowing. Journal of Range Management 54:52-56.

SAS Institute. 2004. SAS/STAT 9.1 User’s Guide. Cary, NC: SAS Institute, Inc. 5136 p.

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 Technology 12:353-362.

Sheley, R.L., J.S. Jacobs, and M.F. Carpinelli. 1999. Spotted knapweed. In: R.L. Sheley and J.K. Petroff (EDS.), Biology and management of noxious rangeland weeds. Corvallis, OR: Oregon State University Press. p. 350-361.

Shirman, R. 1981. Seed production and spring seedling establishment of diffuse and spotted knapweed. Journal of Range Management 34:45-47.

Steel, R. G. D., and J. H. Torrie. 1980. Principles and procedures of statistics: a biometrical approach, 2nd Edition. New York, NY, USA: McGraw-Hill. 633 p.

Thrift, B. D., J. C. Mosley, T. K. Brewer, B. L. Roeder, B. E. Olson, and R. W. Kott. 2008. Prescribed sheep grazing to suppress spotted knapweed on foothill rangeland. Rangeland Ecology and Management 61:18-25.

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

Wallander, R. T., B. E. Olson, and J. R. Lacey. 1995. Spotted knapweed seed viability after passing through sheep and mule deer. Journal of Range Management 48:145-149.

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

[WRCC] Western Regional Climate Center. 2008. Period of record monthly climate summary, Ovando 9 SSE, Montana (246304). Available at: http://www.wrcc.dri.edu. Accessed 23 May 2008.

Research conclusions:

The measurable impacts of this project are widespread and the success of the project was evaluated in several ways, including methods of self-evaluation, external evaluation and outreach evaluation. Measurable deliverables produced and disseminated for information from this project include:

1) three field days,

2) 17 presentations at meetings, workshops, conferences and field days,

3) two published outreach publications,

4) incorporation of results into a Montana State University Extension Bulletin that assimilates existing research and empirical knowledge into a grazing prescription for suppressing spotted knapweed (in progress),

5) one Master’s thesis,

6) four abstracts in proceedings of professional meetings,

7) a Final Project Summary document (i.e., Western SARE Final Report), and

8) one refereed journal manuscript in Rangeland Ecology and Management.

Additionally, through presentation of data and information from this project at meetings, workshops, conferences and field days, I had 21.35 hours of educational contact with groups that included producers, landowners, county extension personnel, weed supervisors, land management agency personnel, researchers and concerned citizens. In that time, I disseminated information to 688 individuals through presentations, handouts and field visits. I have had hundreds of individual contacts regarding the results of this project with landowners and sheep producers since the project’s inception.

In the future, I expect the results of this study to impact at least one-half of the 3.8 million acres of rangeland, pastureland, cropland, forests and wildlands in Montana and the acreage in the other 10 western states that are currently infested with spotted knapweed through the administration of refined or newly adopted grazing protocols that promote good stewardship of those lands. Economically, I expect that, in areas where infestations are so large that herbicide treatment is unfeasible and/or environmental concerns related to herbicides exist, control costs would be reduced by a minimum of 85% by using sheep grazing to control spotted knapweed compared to costs of herbicide treatment. Additionally, in situations where sheep are incorporated into an existing cattle ranch and the enterprise is diversified, the inclusion of two additional food and fiber products, meat and wool from sheep, into marketing plans will enhance the sustainability of these western ranches. Ultimately, with increased dependence on sheep to control spotted knapweed in the West, lamb and wool markets may be bolstered with increased marketing opportunities for producers.

Environmentally, I expect the results of this study to be used in a manner that positively impacts the ecological integrity of the 3.8 million acres of Montana and the acreage in the other 10 western states that are infested with spotted knapweed. The refinement of a control technology that involves sheep grazing or mowing will help reduce the amount of potentially toxic materials applied to these areas, enhance biodiversity, increase available forage for livestock and wildlife, and decrease surface water runoff, soil erosion and sediment yield in streams by reducing spotted knapweed infestation. Lastly, I expect the quality of life for farmers and ranchers impacted by spotted knapweed invasions and the social welfare of rural communities in those areas to be enhanced through the knowledge gained in this project. The combination of enhanced ecological integrity of the land farmers and ranchers depend upon and the economic potential for enterprise diversification on western ranches where prescribed livestock grazing is incorporated ensures the economic and environmental sustainability of western farms and ranches and the economic and social stability of rural, western communities.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Publications:

Mosley, J.C., and T.K. Mosley. In progress. Targeted livestock grazing for vegetation management: grazing and browsing prescriptions for Montana forests and rangelands. Montana State University Extension Service Bulletin. Montana State University, Bozeman, MT.

Benzel, K., T. Mosley, and J. Mosley. 2009. Defoliation timing effects on spotted knapweed seed production and viability, p. 84-90. In: Montana State University Sheep Program Highlights, Department of Animal and Range Sciences.

Benzel, K.R., T.K. Brewer (Mosley), and J.C. Mosley. 2009. Defoliation timing effects on spotted knapweed seed production and viability. Rangeland Ecology and Management 62:550-556.

Mosley, T.K., K.R. Benzel, and J.C. Mosley. 2009. Effects of timing of defoliation on spotted knapweed seed production and viability [poster]. National Association of County Agriculture Agents Meeting. Portland, OR.

Benzel, K.R. 2008. Defoliation effects on spotted knapweed seed production and viability. M.S. [thesis]. Bozeman, MT, USA: Montana State University. 53 p.

Benzel, K.R., T.K. Brewer (Mosley), and J.C. Mosley. 2007. Does timing of defoliation affect spotted knapweed seed production, viability, and germination? [poster]. Society for Range Management Annual Meeting. Reno, NV.

Benzel, K., T. Brewer (Mosley), and J. Mosley. 2007. Effects of timing of defoliation on spotted knapweed seed production and availability, p. 16-17. In: Montana Wool Growers Association Sheep Advisory Committee Report, Montana State University, Bozeman.

Abstracts in Proceedings:

Mosley, T.K., K.R. Benzel, and J.C. Mosley. 2009. Effects of timing of defoliation on spotted knapweed seed production and viability. Abstract. National Association of County Agriculture Agents Meeting. Portland, OR.

Mosley, T.K., K.R. Benzel, S.L. Henderson, and J.C. Mosley. 2009. Prescribed sheep grazing: an effective and compatible tool to suppress spotted knapweed on cattle ranches. Abstract. National Association of County Agriculture Agents Meeting. Portland, OR.

Benzel, K.R., T.K. Brewer (Mosley), and J.C. Mosley. 2008. Effects of timing of defoliation on spotted knapweed seed production and viability. Abstract. Society for Range Management Annual Meeting. Louisville, KY.

Benzel, K.R., T.K. Brewer (Mosley), and J.C. Mosley. 2007. Does timing of defoliation affect spotted knapweed seed production, viability, and germination? Abstract. Society for Range Management Annual Meeting. Reno, NV.

Education and Outreach Programs:

Prescribed Grazing for Weed Management. 2009. Madison County Rancher’s Roundtable, Sheridan, MT.

Prescribed grazing for weed management. Intertribal Agriculture Council – Indian Nations Conservation Alliance (IAC – INCA) Annual Meeting. 2009. Las Vegas, NV.

Defoliation timing effects on spotted knapweed seed production and viability. 2009. Montana State University Montana Wool Growers Association Sheep Advisory Committee Meeting, Department of Animal and Range Sciences.

Effects of timing of defoliation on spotted knapweed seed production and viability. 2009. National Association of County Agriculture Agents Meeting. Portland, OR.

Prescribed livestock grazing for weed management. 2008. Western Region Agriculture Agent Update, Dillon, MT.

Prescribed grazing for weed management: MSU research results. 2008. Granite County Pesticide Applicator Training, Philipsburg, MT.

Prescribed grazing for weed management. 2008. Park County Pesticide Applicator Training, Livingston, MT.

Effects of timing of defoliation on spotted knapweed seed production and viability. 2008. Multi-Species Grazing Roundtable and Research Group Meeting, Helmville, MT.

Effects of timing of defoliation on spotted knapweed seed production and viability. 2008. Society for Range Management Annual Meeting. Louisville, KY.

Effects of timing and intensity of defoliation on spotted knapweed seed production and viability. 2008. Montana Weed Control Association Annual Meeting, Great Falls, MT.

Effects of timing of defoliation on spotted knapweed seed production and viability. 2007. Multi-Species Grazing Roundtable and Research Group Meeting, Helmville, MT.

Sequential cattle and sheep grazing to control spotted knapweed &amp; Effects of timing and intensity of defoliation on spotted knapweed seed production and viability. 2007. Blackfoot Challenge Weed Management Field Tour, Helmville, MT.

Sequential cattle and sheep grazing to control spotted knapweed &amp; Effects of timing and intensity of defoliation on spotted knapweed seed production and viability. 2007. 5th Annual Joe Skeen Institute for Rangeland Restoration Meeting and Field Tour, Helena and Greenough, MT.

Effects of timing and intensity of defoliation on spotted knapweed seed production and viability. 2007 International Mountain Section of the Society for Range Management Summer Meeting and Field Tour, Lubrecht, MT.

Effects of timing of defoliation on spotted knapweed seed production. 2006. Multi-Species Grazing Roundtable and Research Group Meeting, Helmville, MT.

Effects of timing of defoliation on spotted knapweed seed production and viability. 2007. Montana State University Montana Wool Growers Association Sheep Advisory Committee Meeting, Department of Animal and Range Sciences.

Does timing of defoliation affect spotted knapweed seed production, viability, and germination? 2007. Society for Range Management Annual Meeting. Reno, NV.

Educational Program Evaluation:

I proposed to use several measures to evaluate the success of my educational programs, including: 1) the number of people in attendance at meetings, field days, and conferences where I present results, 2) the number of educational contact hours I have with producers, landowners, county extension personnel, weed supervisors, land management agency personnel, researchers and concerned citizens, 3) personal communication with landowners and sheep producers who have included results from this research into their management systems regarding their experiences and perceptions, and 4) the number of acres where my results are incorporated into spotted knapweed control projects of the Montana Sheep Institute. I feel that this project was extremely successful. Each evaluation item is addressed below:

There were 688 people present at the meetings, field days and conferences where results and information from this study were presented.

Total contact hours with producers, landowners, county extension personnel, weed supervisors, land management agency personnel, researchers and concerned citizens tallied 21.35 hours.

I have had hundreds of individual contacts regarding the results of this project with landowners and sheep producers since the project’s inception. Discussions have occurred with sheep owners grazing spotted knapweed and sheep owners considering grazing spotted knapweed, as well as landowners using sheep to control spotted knapweed and landowners considering using sheep to control spotted knapweed.

The Montana Sheep Institute, a Montana State University program that pairs landowners who desire prescriptive grazing for weed control with sheep producers who are willing to use their sheep for weed control and provides outreach assistance to ensure the success of these collaborative partnerships, incorporated results of this study into several grazing projects involving spotted knapweed. However, the exact acreage of spotted knapweed grazing projects is unknown. In general, these projects documented a reduction in the biomass of spotted knapweed over time when multiple years of sheep grazing occurred.

Additionally, I submitted Montana State University Extension-endorsed evaluations to class participants at three of the programs to get feedback on the program/information. Items such as the educational value of the program, program delivery and stimulation of future use of the information were included in the evaluations. Evaluations from 115 participants averaged 4.56 points out of a possible 5 points.

Project Outcomes

Project outcomes:

Spotted knapweed is found in all 11 western states, currently exists in every Montana, Idaho, Wyoming and Washington county, and covers 3.8 million acres of rangeland, pastureland, cropland, forests and wildlands critical for agricultural production in Montana. Knapweed causes more than $42 million in losses annually to Montana’s economy in direct and indirect costs, including a $36 million loss associated with grazing lands and livestock production, a $2.6 million loss in wildlife-associated benefits such as wildlife habitat, hunting, photography, and other wildlife-related recreation, and a $3.4 million loss related to soil and water conservation. Money lost to knapweed in Montana could support 518 full time jobs in the state annually.

It is estimated that the spread rate of spotted knapweed is 10% per year and that ground control for weed management costs landowners, ranchers and agencies a minimum of $25.00 per acre, excluding labor and equipment costs. Additionally, for long-term control, annual reapplication of herbicides is necessary until the seedbank is depleted.

Recent estimates quoted by the Montana Sheep Institute of the cost of weed control with prescribed grazing have been approximately $3.81 per acre. This estimate includes trucking, herding, camp tending and increased death rates. Based on these figures, the cost of controlling spotted knapweed on rangelands in Montana alone could be reduced by nearly 85% if prescribed sheep grazing was used in the place of herbicide application.

There are some risks associated with adopting this practice. First, prescribed grazing requires a strategic approach that exceeds the benefits of simply turning livestock out into a pasture and walking away. If an appropriate strategy is not employed, the potential for landscape degradation increases. Secondly, a quarantine protocol for animals moving away from infestations to uninfested areas at certain times of the grazing season should be included in a grazer’s strategy to minimize the potential for causing new infestations. Sheep do not need to be quarantined before moving to a new area if sheep graze spotted knapweed during the bolting or late-bud/early-flower stages, because spotted knapweed plants at these phenological stages do not contain viable seed. However, sheep that prescriptively graze only once per summer during the full-flower stage should be quarantined in a corral for seven days to allow viable seeds to be excreted before moving the sheep to a new area.

Farmer Adoption

My experience when speaking to cattle ranchers regarding the use of prescribed sheep grazing for spotted knapweed control is that there is hesitancy to launch into an additional enterprise. The hesitancy largely stems from the initial start-up costs of building or converting working facilities, fences, etc. to sheep-friendly. However, in areas where livestock owners with sheep available to graze weeds are present, I have experienced great perception of this tool to control spotted knapweed on neighboring ranches, by both parties.

Results of this study are also applicable to mowing, and I have promoted that technique for spotted knapweed control as well. In general, I have found that adoption of mowing practices in areas with confined patches of spotted knapweed is readily adopted. This technique is less practical on landscapes where topography may be diverse. In general, both mowing and prescribed sheep grazing has been widely accepted as tools in an integrated pest management approach for spotted knapweed control.

I estimate that of the 688 individuals who have participated in workshops, meetings, field days and conferences, at least half (344) were farmers/ranchers. Additionally, in the individual contacts I have had throughout the entire course of the study, I would estimate that I have consulted one-on-one with another 300-400 farmers/ranchers regarding effective timings of defoliation to suppress spotted knapweed.

Recommendations:

Areas needing additional study

In relation to this study, protocols for incorporating sheep grazing into cattle production systems need to be studied. There is widespread concern that grazing areas by both sheep and cattle may impact desirable species within the plant community. Therefore, studies or demonstrations addressing different potential cattle-sheep timing combinations that maximally degrade spotted knapweed and minimally impact desirable forage species are needed.

Additionally, the relationship between sheep grazing and biological control should be further investigated to potentially maximize control of spotted knapweed. There is an underlying feeling that grazing will adversely impact biological control agents in spotted knapweed-infested systems. However, if biological control agents are confined to a reduced availability of its host plant, could it potentially have exacerbated effects than when acting alone?

Lastly, there is evidence that cattle will consume spotted knapweed. I saw this effect in a sister-study to this one, where cattle surprisingly removed an average of 40% of aboveground biomass of spotted knapweed in June and July on foothill rangeland. Studies focusing on how age, previous experience, stock density, or supplementation of animals affects spotted knapweed consumption should be considered.

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.