Improving restoration of exotic annual grass-invaded rangelands through activated carbon seed enhancement technologies

Abstract

Cost-efficient strategies for revegetating annual grass-infested rangelands are limited. Restoration efforts typically comprise a combination of pre-emergent herbicide application and seeding to restore desired plant materials. However, practitioners struggle with applying herbicide at rates sufficient to achieve weed control without damaging nontarget species. The objective of this research was to determine if seed enhancement technologies using activated carbon would improve selectivity of the pre-emergent herbicide imazapic. Bluebunch wheatgrass (Pseudoroegneria spicata) seed was either untreated, coated with activated carbon, or incorporated into "herbicide protection pods" (HPPs) made of activated carbon through a newly developed seed extrusion technique. In a grow-room facility, bluebunch wheatgrass seeds were sown in pots that contained seed of the exotic-annual grass downy brome (Bromus tectorum). After planting, pots were sprayed with 70, 105, 140, or 210 g acid equivalent (ae) · ha-1 of imazapic or left unsprayed. Where herbicide was not applied, downy brome biomass dominated the growing space. Imazapic effectively controlled downy brome and untreated bluebunch wheatgrass. Seed coating improved bluebunch wheatgrass tolerance to imazapic at 70 g ae · ha-1. HPPs provided protection from imazapic at all application rates. When untreated seeds and HPPs are compared at the four levels of herbicide application (excluding the no herbicide level), HPPs on average were 4.8-, 3.8-, and 19.0-fold higher than untreated seeds in density, height, and biomass, respectively. These results indicate that HPPs and, to a lesser extent, activated carbon-coated seed have the potential to further enhance a single-entry revegetation program by providing land practitioners with the ability to apply imazapic at rates necessary for weed control while minimizing nontarget plant injury. Additional research is merited for further development and evaluation of these seed enhancement technologies, including field studies, before they can be recommended as restoration treatments. © 2014 The Society for Range Management.