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