Risk, Rate, and Impact of Medusahead Invasion of California Savannas

Project Overview

Project Type: Graduate Student
Funds awarded in 2007: $19,971.00
Projected End Date: 12/31/2008
Grant Recipient: UC Davis
Region: Western
State: California
Graduate Student:
Major Professor:

Annual Reports


  • Animals: sheep


  • Education and Training: on-farm/ranch research
  • Pest Management: weed ecology


    This graduate student project is integrated into a pre-existing USDA Western SARE project (SW06-038) intended to develop grazing-based methods for medusahead (Taeniatherum caput-medusae) control. Using Landsat imagery and ground surveys across several counties, Mh coverage was mapped over 12 Mha of rangeland in the California Central Valley and surrounding foothills. Two small-scale studies indicated that Mh thatch accumulation has little effect on Mh invasion or removal, and that Mh is not competitive against ryegrass in the absence of defoliation. Spatial mapping of “precision grazing” and Mh distribution over treated pastures in Yolo County was conducted and available results are discussed.


    Medusahead (Taeniatherum caput-medusae) is an invasive noxious grass that is unpalatable to livestock and wildlife and slow to decompose (Young 1992, George 1992). Accumulation of medusahead (Mh) residue forms a heavy thatch layer that may inhibit other plant species (Knapp 1998). By 1999, over 5 million acres in central and northern California contained Mh (Miller et al. 1999). Although it spread southward into 10 more California counties during the last decade, there is little original information about impacts or management of Mh. Only one study of environmental factors related to Mh invasion was published (Dahl and Tisdale 1975). As part of a larger parent project I initiated several studies to better understand the distribution of Mh and the processes related to its invasion and control.

    Project objectives:

    1. 1. Create a method to determine the risk that a pasture or a land management unit will be invaded by Mh. Use method to prioritize areas for prevention of new Mh infestation in participating ranches.
      2. Improve effectiveness of precision grazing to control Mh by determining how patch size and density affect utilization by livestock and subsequent Mh spread.
      3. Establish thresholds for Mh control by assessing the effects of Mh spatial distribution and patch size on loss of grazing capacity and biodiversity.
    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.