Individual and combined effects of fall fire and growth-regulator herbicide on annual bromes

Authors: Vermeire, Lance; Rinella, Matthew - Matt; Strong, Dustin

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2021
Publication Date: 3/26/2021
Citation: Vermeire, L.T., Rinella, M.J., Strong, D.J. 2021. Individual and combined effects of fall fire and growth-regulator herbicide on annual bromes. Rangeland Ecology and Management. 76:129–138. https://doi.org/10.1016/j.rama.2021.02.009.
DOI: https://doi.org/10.1016/j.rama.2021.02.009

Interpretive Summary: Wide-spread invasive annual grasses, cheatgrass and Japanese brome, have sudden population increases and compete with native species. Fire, herbicide and grazing each provide various levels of control. We tested the individual and combined effects of fall fire and the herbicide aminopyralid on annual brome control. Treatments were combinations of two fire (no fire; fall fire with 2-yr return interval) and three herbicide (no herbicide; alternate-yr herbicide; annual herbicide) treatments with five replications. Across years, fire doubled bare ground and reduced litter cover to half of that with no fire. Fire had no effect on percent germination of new brome seed. Fire reduced brome biomass one or two growing seasons after fire. With fire, brome biomass did not exceed 29 kg · ha-1 the first three study years and was 132 kg · ha-1 without fire. During the final year, brome biomass increased and was similar (704 kg · ha-1) across fire treatments. Biomass of all species except brome was 19% greater with fire during 2015 and 2018. Nonburned plots shifted from dominance by cool-season perennial grasses to dominance by bromes by the last year. Cool-season perennial grasses maintained dominance through 2017 with fire and was codominant with bromes during 2018. Aminopyralid reduced brome germination each year it was applied. Despite the reduction in germinable seed, brome biomass was not affected by herbicide. Cool-season perennial grasses dominated in both herbicide treatments through 2017. During 2018, bromes dominated with no herbicide or alternate-yr herbicide and were codominant with cool-season perennial grasses with annual herbicide treatment. All treatment combinations reduced forbs compared to nonburned, no herbicide treatment. Long-term control of annual bromes requires long-term commitment to repeated treatment. Complementary treatment combinations could increase control if they address different phases of the brome life cycle. However, the combination of fall fire and spring application of aminopyralid did not extend annual brome control under the study conditions.

Technical Abstract: Wide-spread invasive annual grasses, cheatgrass (Bromus tectorum L.) and Japanese brome (B. japonicus Thunb.), have sudden population increases and compete with native species. Fire, herbicide and grazing each provide various levels of control. We tested the individual and combined effects of fall fire and the herbicide aminopyralid on annual brome control. Treatments were a factorial arrangement of two fire (no fire; fall fire with 2-yr return interval) and three herbicide (no herbicide; alternate-yr herbicide; annual herbicide) treatments with five replications. Across years, fire doubled bare ground and reduced litter cover to half of that with no fire. Fire had no effect on percent germination of new brome seed. Fire reduced brome biomass one or two growing seasons after fire. With fire, brome biomass did not exceed 29 kg · ha-1 the first three study years and was 132 kg · ha-1 without fire. During the final year, brome biomass increased and was similar (704 kg · ha-1) across fire treatments. Nonbrome biomass was 19% greater with fire during 2015 and 2018. Nonburned plots shifted from dominance by C3 perennial grass to dominance by bromes by the last year. C3 perennial grass maintained dominance through 2017 with fire and was codominant with bromes during 2018. Aminopyralid reduced brome germination each year it was applied. Brome biomass was not affected by herbicide. C3 perennial grass dominated in both herbicide treatments through 2017. During 2018, bromes dominated with no herbicide or alternate-yr herbicide and were codominant with C3 perennial grass with annual herbicide treatment. All treatment combinations reduced forbs compared to nonburned, no herbicide treatment. Long-term control of annual bromes requires long-term commitment to repeated treatment. Complementary treatment combinations could increase control. However, the combination of fall fire and spring application of aminopyralid did not extend annual brome control under the study conditions.