Using herbicides to control an invasive annual grass, Ventenata dubia, in southwestern Montana

Herbicides are often used to control invasive annual grasses with varying degrees of success. In this study, the effectiveness of active ingredient, indaziflam (Esplanade), a new herbicide mode of action, was compared to commonly used herbicides for controlling Ventenata dubia (ventenata), while accounting for injury of the local plant community. Indaziflam is a cellulose biosynthesis inhibiting herbicide which has activity on plant roots. Applied prior to seedling emergence, it is expected to control annual species for up three years. In a Bromus inermis (smooth brome) dominated field near Bozeman, MT, 10 herbicide treatments were applied fall 2016. Assessments of V. dubia control and injury to co-occurring species were conducted three times throughout the 2017 and 2018 growing season. Canopy cover of V. dubia, annual forbs, perennial grasses, perennial forbs, and bare ground were measured. Our results indicate indaziflam provides at least two years of control of V. dubia alone and in combination applications, however, varying degrees of injury to perennial grasses are evident. Increased bare ground can also cause potential niche openings and erosion issues. Information obtained through this study will be useful for restoring disturbed range and wild lands that are impacted by invasive annual grasses like V. dubia.