Ventenata and other coexisting exotic annual grass control and plant community response to increasing imazapic application rates

Authors: Davies, Kirk; Hamerlynck, Erik

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2019
Publication Date: 7/1/2019
Citation: Davies, K.W., Hamerlynck, E.P. 2019. Ventenata and other coexisting exotic annual grass control and plant community response to increasing imazapic application rates. Rangeland Ecology and Management. 72(4):700-705. https://doi.org/10.1016/j.rama.2019.02.010.
DOI: https://doi.org/10.1016/j.rama.2019.02.010

Interpretive Summary: Ventenata (Ventenata dubia (Leers) Coss.) is an exotic annual grass invading Intermountain rangeland plant communities, where it can form monotypic stands, degrade wildlife habitat, and reduce livestock forage. We evaluated five application rates of imazapic (0 to 175 g ae·ha-1) on ventenata control and plant community response at two rangeland sites in two years (2014 and 2015). Ventenata control increasing within increasing imazapic rates. However, control was not enough to shift the dominance from exotic annual species to perennial species and exotic annual grasses fully recovered by the second or third year after imazapic application. This information is useful to rangeland managers and scientists developing strategies to manage ventenata.

Technical Abstract: Ventenata (Ventenata dubia (Leers) Coss.) is an exotic annual grass that can invade Intermountain rangeland plant communities, where it can form monotypic stands, degrade wildlife habitat, and reduce livestock forage. There is limited information on ventenata control in rangelands as it has only recently be identified as a substantial problem. Imazapic is a pre-emergent herbicide commonly used to control other exotic annual grasses and therefore, is likely to control ventenata in rangelands. We evaluated five application rates of imazapic (0 to 175 g ae·ha-1) on ventenata control and plant community response at two rangeland sites in two years (2014 and 2015). Imazapic reduced exotic annual grass (largely ventenata) cover and density, with greater vententata control with increasing imazapic rates. Exotic annual grass density at the highest levels of control was 184-299 plants·m-2 the first year after imazapic application. Exotic annual grasses fully recovered in the second or third year after imazapic application. Bare ground generally increased with imazapic application. However, density of perennial vegetation did not vary among treatments. Perennial vegetation cover generally did not increase with imazapic control of ventenata. Imazapic can control ventenata; however, even at the highest rates, control was not enough to shift the dominance from exotic annual species to perennial species. Integrating other treatments with imazapic application may be a strategy to improve ventenata control and increase perennial vegetation, and will require further investigation. The difficulty and likely expense of achieving substantial and lasting control of ventenata suggest, similar to other exotic annual grasses, that preventing ventenata invasion and dominance should be a high management priority.