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Mailing Address:
U of I Moscow
Natural Resources Bldg.
Room 205
875 Perimeter Dr. MS 1135
Moscow, ID 83844-1135
Phone: 208-885-6536  
Fax: 208-885-6564

Physical and Mailing Address: 
U of I Boise
Idaho Water Center
Suite 242 
322 E Front St.
Boise, ID 83702
Phone: 208-364-3176

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Assessing the Effectiveness of New Herbicides for Managing Invasive Weeds on Rangelands

The Challenge

Managing annual invasive grasses is tremendously difficult due to their rapid growth and reproduction, allowing them to outcompete native plants and spread across vast areas at a rapid rate. As they continue to colonize new areas, they are reshaping the range by reducing wildlife and livestock food resources and increasing the wildfire return interval.

Aerial application of herbicides has been key for managing invasive annual grass species. Through this method, herbicides can be applied to large areas to reduce spread of the invasive grasses on the landscape, lessen fire risk, and potentially reduce the size of wildfires.

Cheatgrass, an invasive annual grass
Figure 1: An area dominated by Cheatgrass, an invasive annual grass

Imazapic, an herbicide active ingredient, is commonly used for aerial applications and is effective for controlling annual invasive grasses for at least one year. Although effective, annual application over large landscapes is labor and cost-intensive.

A new herbicide, indaziflam, has been shown to be effective for up to three years. A longer-acting herbicide could be very beneficial for controlling annual invasive grasses, but little information is available about the effectiveness of indaziflam with aerial application.  

A treatment plot from a study on cheatgrass.
Figure 2: A treatment plot from the study, with new forbes and native plants rapidly recolonizing the area.

Our Response

A study spearheaded by Rangeland Center Members Lisa Jones and Dr. Tim Prather is assessing the effectiveness of aerial application of indaziflam, both by itself and co-applied with imazapic. This study is also diving in to whether this combination of herbicides negatively affects the reestablishment of native vegetation after the annual grasses are removed.  

So far, the herbicide has been successfully controlling annual grasses for three years. Forbs, shrubs, and grasses are starting to establish in the treated areas. Early results for indaziflam are promising, and continued study of this herbicide may help develop more effective strategies for managing the risks of invasive annual grasses in sage steppe ecosystems.

Contact Us

Mailing Address:
U of I Moscow
Natural Resources Bldg.
Room 205
875 Perimeter Dr. MS 1135
Moscow, ID 83844-1135
Phone: 208-885-6536  
Fax: 208-885-6564

Physical and Mailing Address: 
U of I Boise
Idaho Water Center
Suite 242 
322 E Front St.
Boise, ID 83702
Phone: 208-364-3176

Directions