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

Project Overview

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
Dr. Tracy Mosley
Montana State University Extension

Annual Reports


  • Additional Plants: native plants


  • Animal Production: range improvement
  • Education and Training: demonstration, extension, farmer to farmer, focus group, on-farm/ranch research, participatory research
  • Natural Resources/Environment: habitat enhancement
  • Pest Management: weed ecology

    Proposal abstract:

    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 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.

    Project objectives from proposal:

    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 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.

    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.