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Bio-control of Invasive Grasses in the Mojave Desert

Competition from annual bromes (cheatgrass and red brome) is a major obstacle to post-fire seeding success in arid ecosystems. Because currently available control methods fail to eliminate the annual brome carryover seedbank, we are examining the native fungal pathogen Pyrenophora semeniperda as a bio-control organism to eliminate these carryover seeds. Studies completed so far have shown that:

  1. Isolates of the fungus vary widely in virulence. Virulence variation is negatively correlated with growth rate in culture.
  2. This variation is genetically based, and multiple strains of the P. semeniperda can infect the same seed.
  3. Following application, the fungus persists at least one year under field conditions. This may necessitate fungicide treatment of seeds following bio-control, and further suggests that current and past seeding failures in arid ecosystems may already be associated with the fungus.
  4. While a fraction of brome seeds were killed by the heat associated with fires, infected seeds that were not burned up were still able to produce conidia.
  5. Using P. semeniperda to control brome seeds in lab and field studies has been good to excellent so far. Taken as a whole, these results suggest excellent potential for Pyrennophora semeniperda as a bio-control for seeds of cheatgrass and red brome.
  6. The outcome following infection for annual brome seeds is a “race” between the germinating embryo and the fungus, both of which compete for endosperm reserves. For this reason, dormant or slowly germinating seeds are most likely to be killed by the fungus.
  7. P. semeniperda has many hosts, including native grasses, forbs and shrubs. Susceptibility to the fungus among species varies widely.


  • Phil Allen, Craig Coleman, Mikel Stevens, Department of Plant and Wildlife Sciences (College of Life Sciences) BYU
  • Susan Meyer, US Forest Service Shrub Sciences Laboratory
  • Julie Beckstead, David Boose, Gonzaga University

This research project is funded by: The USDA National Research Initiative, the USDA Forest Service, the Nature Conservancy, and the Joint Fire Science Program; with logistical support from the Bean Life Science Museum’s Lytle Ranch Preserve.