Does Timing of Defoliation Affect Spotted Knapweed Seed Viability and Germination?

Does Timing of Defoliation Affect Spotted Knapweed Seed Viability and Germination?

Summary

Spotted knapweed, an extremely 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 is a tool used to control spotted knapweed that offsets high costs of control with herbicides and environmental concerns surrounding herbicides. However, research focused on specific details of grazing prescription protocols for spotted knapweed control at a landscape scale is in its infancy. The purpose of this proposed research is to determine the ideal timing(s) or combination(s) of timings of defoliation on spotted knapweed to maximally reduce flowerhead and viable seed production, and minimize seed incorporation into the seedbank.

Objectives/Performance Targets

Objective 1: Evaluate the effects of timing of defoliation of spotted knapweed 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 defoliation of spotted knapweed 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.

Accomplishments/Milestones

Year 1 Accomplishments:

Objective 1: Clipping treatments were applied to spotted knapweed plants in June, July, and August and first-year data were successfully collected by mid-fall. Laboratory analyses of the spotted knapweed seeds was also successfully completed by winter. During the laboratory analysis process, 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 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 viability. Data for Year 1 were analyzed for presentation of preliminary results.

Objective 2: We have been working with Montana livestock owners and landowners with spotted knapweed infestations, as well as the Montana Sheep Institute, to apply what we have learned in Year 1 to grazing management situations on the landscape.

Objective 3: Preliminary results of this research have been presented to a variety of groups. Results were presented to the Multi-Species Grazing Roundtable and Research Group on two occasions (fall, spring), resulting in the information being conveyed to approximately 40 participants. Results were also presented in poster format at the international Society for Range Management annual meeting in Reno, NV, to approximately 75 participants at a Weed Management Field Day hosted by the Blackfoot Challenge, and to 35 participants at the 5th Annual Joe Skeen Institute for Rangeland Restoration Annual Meeting and Field Tour.

Year 2 Accomplishments:

Objective 1: Clipping treatments for Year 2 were applied to spotted knapweed plants in June, July, and August and second-year data were collected by mid-fall. Laboratory analyses for Year 2 were also completed by early winter. Data analysis and synthesis of combined data from Years 1 and 2 is in progress.

Objective 2: Information gleaned from this project in collaboration with the Multi-Species Grazing Roundtable and Research Group has been incorporated into a Montana State University bulletin. This bulletin is a defined livestock grazing prescription for controlling spotted knapweed that clearly describes the appropriate timing, intensity, frequency, and duration of grazing, as well as appropriate stocking rates and monitoring indicators for sustainable grazing. This publication is currently in draft form and is expected to be published in 2009. Additionally, we have continued to work with livestock producers and landowners who are utilizing prescribed livestock grazing or mowing to manage spotted knapweed. We have also continued to collaborate with the Montana Sheep Institute (MSI) to provide results for use on MSI projects.

Objective 3: Final results will be presented where opportunities arise to share important findings of this research. Results have been presented at the international Society for Range Management Annual meeting in Louisvile, KY, at a fall meeting of the Multi-Species Grazing Roundtable and Research Group, at the Montana Weed Control Association annual meeting, and at Joe Skeen Institute for Rangeland Restoration field day. Additional presentations of results will occur when the opportunity arises. Additionally, we will publish a Master’s thesis, a popular press article, and a refereed journal manuscript in Rangeland Ecology and Management.

Year 3 Accomplishments:

Objective 1: Data analyses and synthesis from years 1 and 2 were completed.

Objective 2: Data and information from this project have been combined with information from previous research and existing grazing prescription protocols to create a refined, more precise grazing prescription for spotted knapweed. In cooperation with the Multi-Species Grazing Roundtable and Research Group and many other interested parties, the refined grazing prescription protocol has been distributed throughout Montana to be used on spotted knapweed-infested rangeland. The information has also been incorporated into a Montana State University bulletin, which is a defined livestock grazing prescription for controlling spotted knapweed that clearly describes the appropriate timing, intensity, frequency, and duration of grazing, as well as appropriate stocking rates and monitoring indicators for sustainable grazing. This publication is currently in draft form and is expected to be published in 2010. Upon completion of this bulletin, copies will be distributed to all county Extension offices in Montana and we will work to promote the associated management techniques across Montana and the West.

Objective 3: Information gleaned from this project has been shared with a vast assortment of individuals and groups interested in spotted knapweed control. Results and applications have been shared with ranchers, landowners, livestock operators, county Extension personnel, county weed district personnel, state and federal agency personnel, university researchers, and other concerned citizens. Information has been distributed at field days and workshops, as well as conferences in Montana and the western U.S. We estimate that this information and practical applications associated with it has been presented to >500 people throughout the course of this project.
We have continued to work one-on-one with livestock producers and landowners who are utilizing prescribed livestock grazing or mowing to manage spotted knapweed. These interactions have provided a great opportunity to help individuals and groups with spotted knapweed problems focus their efforts on reducing viable seed input into the seedbank, which ultimately reduces control costs on their land and enhances the ecological integrity of their rangelands.

A Master’s of Science student successfully completed her coursework and research requirements using this project and a Master’s thesis was published as a result of this project. Additionally, a peer-reviewed journal manuscript was successfully published in the journal Rangeland Ecology and Management (60:550-556).

There are still ample opportunities to disseminate the important results of this research. Once the Montana State University bulletin is complete, management applications of this research will be disseminated across Montana and the West to promote effective management of spotted knapweed and to promote the enhanced ecological integrity of rangelands.

Impacts and Contributions/Outcomes

Results:

Spotted knapweed produced new buds and flowers by the end of the growing season 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, reduced the percent viability of seeds present at dormancy, and reduced the number of viable seeds present.

Clipped plants produced 73-98% fewer buds/flowerheads than unclipped plants. All seven clipping treatments also reduced seed production by spotted knapweed. 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%.

No seeds in the doughy stage were viable throughout the study and clipping in June during the bolting stage reduced percent viability of intermediate seeds 57%. Clipping at all other timings or combinations of timings reduced percent viability of intermediate seeds 99% compared with no clipping. 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% and clipping at all other timings or combinations of timings reduced percent viability of mature seeds 58-99.6%.

The numbers of viable intermediate, mature, and total seeds were all reduced by clipping. Clipping in June during the bolting stage reduced the total number of viable seeds nearly 90% compared with no clipping. 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.

Management Implications/Application:

Defining the most effective timing of defoliation of spotted knapweed to reduce viable seed production is critical for suppressing spotted knapweed. Spotted knapweed reproduces largely by seed, therefore, prescribed sheep grazing or mowing should effectively suppress its reproduction when spotted knapweed is defoliated during the bolting, late-bud/early-flower or full-flower stages. New flowers that are produced after defoliation earlier in the same summer produce very few to no viable seeds. Defoliation during the bolting stage can reduce the number of viable seeds nearly 90%, but the most effective time of defoliation is during the late-bud/early-flower or full-flower stage, which reduces viable seed production nearly 100%.

Defining the most effective timing of defoliation of spotted knapweed to reduce viable seed production is critical for suppressing spotted knapweed. Livestock owners and landowners who are using applied prescribed sheep grazing or mowing to control spotted knapweed can benefit greatly from knowing when the most effective timing of grazing is, so they can fine-tune their grazing strategies to most effectively treat their spotted knapweed-infested rangeland. Results from this research indicate that if spotted knapweed is prescriptively grazed or mowed during the bolting stage, an additional defoliation during the late-bud/early-flower or full-flower stage is recommended for the best control. However, if spotted knapweed plants are prescriptively grazed or mowed during the late-bud/early-flower or full-flower stage, an additional defoliation is not necessary.

Collaborators: