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Johnson Creek WHMA
Cheatgrass Control/Herbicide Application

The Johnson Creek Wildlife Habitat Management Area (WHMA) encompasses 2,880 acres in Sybille Canyon, and serves as yearlong and crucial winter range for mule deer, elk, bighorn sheep, and antelope. The area receives high recreational use (hunting, fishing, wildlife viewing) from the public throughout the year. In August of 2001, a wildfire burned 448 acres of the unit. Post-burn, cheatgrass emergence was almost immediate. Fire intensities were severe enough that response of perennial vegetation was negatively impacted. Nearly all mixed mountain shrubs were lost, particularly on south facing aspects. Cheatgrass provides only limited seasonal forage value for wildlife, and its prevalence raised the concern of local Department personnel, as well as private landowners and other land management agencies in the area.

In an effort to maintain the unit as an important seasonal and yearlong range for big game species, restoration efforts involving herbicides were considered. In Fall 2001, small test plots were completed on the unit, within and outside of the burn perimeter, using a herbicide called Plateau ®. Rates used varied from 2 oz./ acre to 12 oz./acre. By Spring of 2002, positive results (100% control of cheatgrass) were seen where the herbicide was applied. Plans were put in place to treat the majority of the burn area in early Fall 2002. Joe Vollmer of BASF provided Department personnel with herbicide application rate and timing of treatment recommendations.

In late August 2002, Plateau® was applied at a rate of 8 oz. / acre through aerial / helicopter application. In addition, 1 quart / acre of methylated seed oil surfactant and 5 gallons of water / acre was also used. Approximately 82% of the burn area was treated with herbicide. The other 18% is under federal ownership, and application of Plateau ® is not yet approved for use on these lands. Federal lands in the burn area were considered the "Control" for monitoring purposes. In addition, 89 acres of unburned lands were also treated at the same rate to control heavy cheatgrass infestations found in the understory of mixed mountain shrub stands. Costs for treatment were as follows: Herbicide and Surfactant $8,686.90, Aerial Application $8,264.00, Total Cost $16,950.90, for a Cost per Acre Treated of $37.67. Costs for the project were shared by the Wyoming Game and Fish Department, Foundation for North American Wild Sheep, and Rocky Mountain Elk Foundation.

Transects have been established in and outside of the treatment area, to monitor the herbicide's effects on targeted and non-targeted species.

Results from 2003, one year post-treatment, are:

  • 100% effective control of cheatgrass in treated sites
  • Increase in relative native cover from 15.8% to 100% in treated sites
  • 25% native cover in untreated sites, 75% is cheatgrass.
  • Percent total (native and non-native) herbaceous cover of 19% in treated sites, 51% in non-treated areas

Results from 2004, two years post-treatment are:

  • 97% effective control of cheatgrass in treated sites (3% decrease from '03)
  • Relative native cover of 91% in treated sites (9% decrease from '03)
  • 26% native cover in untreated sites, 74% is cheatgrass
  • Percent total (native and non-native) herbaceous cover of 32% in treated sites (13% increase from '03), 66% in non-treated areas (15% increase from '03)