Effectiveness of pre-emergent herbicides in rangeland rehabilitation

Authors: Clements, Darin - Charlie; Harmon, Daniel - Dan

Submitted to: California Invasive Plant Council
Publication Type: Abstract Only
Publication Acceptance Date: 9/12/2020
Publication Date: 10/29/2020
Citation: Clements, D.D., Harmon, D.N. 2020. Effectiveness of pre-emergent herbicides in rangeland rehabilitation. California Invasive Plant Council. 7:1-4.

Interpretive Summary:

Technical Abstract: Arid western rangelands of the United States face one of the greatest environmental challenges of the 21st century. The accidental introduction and subsequent invasion of cheatgrass onto millions of acres of Great Basin rangelands has resulted in catastrophic and the conversion of formerly big sagebrush/bunchgrass communities to rangelands dominated by cheatgrass. In an effort to minimize the negative effects of wildfires and habitats converted to cheatgrass dominance, the USDA-Agricultural Research Service, Great Basin Rangelands Research Unit has been conducting research on the use of pre-emergent herbicides to control cheatgrass and reduce the cheatgrass seedling/perennial grass seedling competition that results in perennial grass seedling mortality and ensures cheatgrass dominance. The establishment of perennial grasses is critical in reducing cheatgrass densities and associated fuels. To control cheatgrass and other associated annual weeds we applied Sulfometuron methyl Chlorsulfuron, Landmark XP, @ 1.75 oz/acre rate, and Imazapic, Plateau, @ 6oz/acre rate then fallowed the treated plots for 1-year and seeded desirable native and introduced perennial grasses. Each treated plot received 3 seed mixes; 1) Native, 2) Introduced, and 3) Native/Introduced. The Landmark XP application reduced cheatgrass above-ground densities by 99.3% while Plateau reduced it by 98.6%. This level of cheatgrass control significantly increased available mineral nitrogen and soil moisture for seedlings of seeded species. Perennial grass establishment into the second-year averaged 3.3/ft² in the introduced and native seed mix plots while the native/introduced seed mix plots averaged 2.4/ft². The introduced plots yielded 1 cheatgrass/ft² showing promising suppression of cheatgrass, while the native and introduced plots recorded 3x as much cheatgrass, 3.6 and 3.4 cheatgrass/ft², respectfully. The control plot averaged 22.2/ft² which results in as much as 96% reduction in cheatgrass above-ground densities. This study demonstrates that if we use the best tools in the toolbox including pre-emergent herbicides and adaptable plant species and apply them correctly using proper timing, rates and seeding depths we can be successful and make progress towards a more productive and sustainable rangeland future. It is not prudent to limit your chance of success by seeding without an active weed control program (reducing cheatgrass competition) or applying pre-emergent herbicide at the wrong time (post-emergent) as well as using plant materials that will limit your success and increase the failure rates.