Title: Can imazapic and seeding be applied simultaneously to rehabilitate medusahead-invaded rangeland? Single vs. multiple entry Authors
Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 23, 2014
Publication Date: N/A
Interpretive Summary: Medusahead invasion reduces livestock forage, degrades wildlife habitat, and promotes frequent wildfires. Thus, there is a need to rehabilitate medusahead-invaded rangelands, but rehabilitation can be expensive. To reduce the cost of rehabilitating medusahead-invaded rangelands, it has been proposed that herbicide control with imazapic be applied concurrent with seeding desired species. We compared this method to seeding desired species one year after imazapic application. We found that establishment of seeded species was more than 10 times greater when seeding occurred one year after imazapic application, probably as a result of reduced herbicide mortality of seeded species. Our results suggest that waiting one year to seed after imazapic application is a better rehabilitation strategy than combining seeding and imazapic application into a single treatment.
Technical Abstract: It has recently been proposed that reducing the cost of rehabilitating medusahead (Taeniatherum caput-medusae (L.) Nevski)-invaded rangelands may be attained by seeding desired vegetation with a concurrent application of the pre-emergent herbicide (imazapic). However, the efficacy of this “single entry” approach has been inconsistent and it has not been compared to the multiple entry approach where seeding is delayed one year to decrease herbicide damage to non-target seeded species. We evaluated single and multiple entry approaches at five medusahead-invaded rangelands in southeastern Oregon with seeding for both treatments occurring in October of 2011. Prescribed burns were performed at each single and multiple entry plot prior to imazapic application to improve medusahead control and prepare the seedbed for seeding introduced perennial bunchgrasses. Both treatments effectively controlled medusahead during the two years post-seeding. However, almost no seeded bunchgrasses established with the single entry treatment (< 0.5 individals•m-2); probably as a result of non-target herbicide mortality. In contrast, the multiple entry treatment had on average 6.5 seeded bunchgrasses•m-2 in the second year post-seeding. Perennial grass (seeded and non-seed species) cover was eight times greater in the multiple entry compared to the single entry treatment by the second year post-seeding. Perennial grass cover and density in the single entry treatment did not differ from the untreated control. These results suggest that the multiple entry approach has probably altered the community from annual dominated to perennial grass dominated, but the single entry approach will likely be re-invaded and dominated medusahead without additional treatments because of a lack of perennial vegetation. Our results suggest that if medusahead is successfully controlled with imazapic that a single entry approach will not be effective because of limited establishment of seeded species.