Herbicide protection pods (HPPs) facilitate sagebrush and bunchgrass establishment under imazapic control of exotic annual grasses

Authors: CLENET, DANIELLE - Oregon State University; Davies, Kirk; JOHNSON, DUSTIN - Oregon State University; KERBY, JAY - Nature Conservancy

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2020
Publication Date: 8/26/2020
Citation: Clenet, D.R., Davies, K.W., Johnson, D.D., Kerby, J.D. 2020. Herbicide protection pods (HPPs) facilitate sagebrush and bunchgrass establishment under imazapic control of exotic annual grasses. Rangeland Ecology and Management. 73(5):687-693. https://doi.org/10.1016/j.rama.2020.07.002.
DOI: https://doi.org/10.1016/j.rama.2020.07.002

Interpretive Summary: It is difficult to reliably establish perennial bunchgrasses and shrubs into areas invaded by exotic annual grasses. Herbicide is often necessary to control exotic annual grasses to establish bunchgrasses from seed. This study assessed the effectiveness of seed incorporated into pellets containing activated carbon in protecting multiple species of bunchgrasses and shrubs in the field from high levels of herbicide control of exotic annual grasses. Activated carbon protects seed in pellets by deactivating herbicide, allowing seeding and herbicide application to be done concurrently. We found that pellets protected seed from high levels of herbicide and thus improved establishment of four perennial bunchgrass species and sagebrush. Since revegetation of sagebrush steppe is extremely difficult and is necessary to increasing the resistance and resilience of the sagebrush steppe, any technology which improves the chance of success is extremely valuable.

Technical Abstract: Revegetation of annual grass-invaded rangelands is a primary objective of land managers following wildfires. Controlling invasive annual grasses is essential to increasing revegetation success; however, pre-emergent herbicides used to control annual grasses prohibit immediate seeding due to non-target herbicide damage. Thus, seeding is often delayed one year following herbicide application. This delay frequently allows for re-invasion of annual grasses, decreasing the success of revegetation efforts. Incorporating seeds into herbicide protection pods (HPPs) containing activated carbon (AC) permits concurrent high herbicide application and seeding because AC deactivates herbicides. While HPPs have, largely in green-house studies, facilitated perennial bunchgrass emergence and early growth, their effectiveness in improving establishment of multiple species and functional groups in the field has not been assessed. We seeded five bunchgrass species and two shrub species as bare seed and seed incorporated into HPPs at two field sites with high imazapic application rates to control annual grasses. HPPs significantly improved establishment of sagebrush (Artemesia tridentata Nutt. Spp. wyomingensis Beetle & Young), and crested wheatgrass (Agropyron cristatum (L.) Gaertn.) over the two-year study. Three native perennial grass species were protected from herbicide damage by HPPs but had low establishment in both treatments. The two remaining shrub and grass species did not establish sufficiently to determine treatment effects. While establishment of native perennial bunchgrasses was low, this study demonstrates that HPPs can be used to protect seeded bunchgrasses and sagebrush from imazapic, prolonging establishment time in the absence of competition with annual grasses.