Litter Reduction by Prescribed Burning Can Extend Downy Brome Control

Abstract

LITTER REDUCTION BY PRESCRIBED BURNINGCAN EXTEND DOWNY BROME CONTROL Downy brome (Bromus tectorum L.) is a highly successful invasive species primarily because it fills an open niche in native plant communities. It also produces large amounts of litter over time. We hypothesized that removing accumulated litter with a prescribed burn before applying herbicides would improve herbicide efficacy, extending the duration of control. In January 2012, two downy brome infested sites were burned. In March 2012, post-emergent applications of glyphosate, imazapic, and tebuthiuron were made in a split-plot design.Aboveground biomass was collected at 6, 18 and 27 months after treatment (MAT) to evaluate treatment effects. In non-burned areas, all herbicide treatments were similar to the control 27 MAT; however, burning combined with imazapic or tebuthiuron reduced downy brome biomass 27 MAT by 81% ± 4.6 SE and 84% ± 19.3 SE, respectively. Remnant species responded positively to burning and herbicide treatments. Native cool season grass biomass increased after burning while native warm season grass biomass increased following tebuthiuron treatments.The impact of litter on imazapic and tebuthiuron availability was also evaluated. Herbicide interception increased in a linear relationship with increasing litter. For every 50 g·m -2 increase in litter there was a 7% increase in the amount of herbicide intercepted, meaning that 75% of the applied herbicide was intercepted by 360 g·m -2 of litter. A simulated rainfall event of 5 mm, 7 days after application, removed a significant amount of herbicide. This indicates that at sites with surface litter, timely precipitation could be critical for herbicide efficacy; however, when burning was used to remove litter and was followed by herbicides with residual soil activity, iii downy brome control was extended. Due to downy brome's relatively short seed viability in the soil, extending herbicide efficacy to several years could help to reduce the soil seed bank.iv ACKNOWLEDGEMENTS

The influence of winter annual grass litter on herbicide availability

“…Litter was allowed to dry under the same conditions described previously and was then weighed. The average biomass of the three litter samples was equivalent to 2,600 kg ha −1 , which is consistent with biomass production in high litter sites for all three winter annual grass types (Evans and Young 1970;Kessler et al 2015;Wallace et al 2015). Therefore, this biomass was used to simulate high litter conditions, while 50% of the biomass measurement (1,300 kg ha −1 ) was used to simulate low litter conditions.…”

“…The impacts of winter annual grass litter on soil-active herbicides have only been empirically evaluated in one published study (Kessler et al 2015). In that study, up to 74.6% of imazapic and tebuthiuron were intercepted when applied over high amounts of B. tectorum litter, and only 69% of the intercepted herbicide could be desorbed from the litter with 15 mm of rainfall 7 d after treatment (DAT) (Kessler et al 2015). That study and several others evaluating crop residues have hypothesized that some irreversible binding to the litter may be occurring.…”

“…That study and several others evaluating crop residues have hypothesized that some irreversible binding to the litter may be occurring. This hypothesis is based on the fact that rainfall is not able to recover 100% of the applied herbicide (Banks and Robinson 1982;Carbonari et al 2016;Cavenaghi et al 2007;da Silva 2018;Ghadiri et al 1984;Kessler et al 2015).…”

Accounting for aboveground carbon storage in shrubland and woodland ecosystems in the Great Basin

“…For example, in the Great Basin, introduced grassland is primarily cheatgrass which has aboveground carbon typically below 1000 kgC/ha (Bradley et al 2006, Diamond et al 2012, Kessler et al 2015. Our excluded category included primarily agriculture, introduced grass, development, and water.…”

“…These vegetation types typically store small amounts of aboveground carbon. For example, in the Great Basin, introduced grassland is primarily cheatgrass which has aboveground carbon typically below 1000 kgC/ha (Bradley et al 2006, Diamond et al 2012, Kessler et al 2015. While on average, agriculture systems in the United States store some carbon, it is typically harvested, resulting in little long-term aboveground carbon storage.…”