Susceptibility of native annual forbs to indaziflam and imazipic

Authors: Harmon, Daniel - Dan; Clements, Darin - Charlie

Submitted to: Society for Range Management
Publication Type: Abstract Only
Publication Acceptance Date: 12/21/2020
Publication Date: 2/16/2021
Citation: Harmon, D. N. and C. D. Clements. 2021. Susceptibility of native annual forbs to Indaziflam and Imazapic. Society for Range Management Virtual Annual Meeting, February 15-18,2021. 74:63. #379818

Interpretive Summary:

Technical Abstract: Management techniques to minimize the negative impacts of exotic plant invasions can include a diverse array of tools. One such tool is the use of pre-emergent herbicides. These herbicides, if used correctly, pose little threat to established perennial plants and are extremely effective on newly germinated seeds. The primary target for most rangeland pre-emergent herbicides is annual grasses. However, the unintended costs to native annual forb populations has not been well studied. Broadleaf native annual forbs likely vary in their susceptibility to different pre-emergent herbicides. Annual forbs have complex seed dormancy strategies that lead to persistent seedbanks that may outlast the herbicide activity period. Imazipic has about a 1-year activity period, which can vary depending on environmental conditions. The recently developed herbicide Indaziflam has a longer activity period beyond 1 year. We designed a field experiment to evaluate the susceptibility of native annual forbs to these herbicides. At two field sites in northern Nevada, we seeded replicated plots (1m2) of 5 different native annual forbs. Plots were seeded October 2019 on (1) non-herbicide treated plots, plots 1 year after (2) Imazipic and (3) Indaziflam treatments (sprayed September 2018) and plots the same year as (4) Indaziflam application (sprayed September 2019). Monitoring occurred in May 2020. Overall, the reduced cheatgrass competition and decreased herbicide activity on Imazipic plots lead to the greatest forb establishment densities (2018 Imazipic: 83 seedlings/m2, non-herbicide: 34 seedlings/m2, 2018 Indaziflam: 7 seedlings/m2, and 2019 Indaziflam: 0.5 seedlings/m2). These results indicate that Indaziflam is remaining active the second year after application, however some seedling establishment did occur, demonstrating the potential to replenish the annual forb seedbank for long-term persistence. Replicated plots were seeded in October 2020 and monitoring will continue on previous and newly established plots to determine the long-term effects of these herbicides on native annual forbs.