The benefits of using pre-emergent herbicides in rehabilitating cheatgrass-infested rangelands

Authors: Morgan, Tye; Harmon, Daniel - Dan; Blank, Robert - Bob; Clements, Darin - Charlie

Submitted to: The Progressive Rancher
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/19/2018
Publication Date: 7/12/2018
Citation: Morgan, T.A., Harmon, D.N., Blank, R.R., Clements, D.D. 2018. The benefits of using pre-emergent herbicides in rehabilitating cheatgrass-infested rangelands. The Progressive Rancher. 7:14-15.

Interpretive Summary: Arid western rangelands of the United States face one of the greatest environmental challenges of the 21st century, cheatgrass invasion and the resulting reoccurring wildfires. With each passing wildfire season, more and more critical habitats are being converted to cheatgrass grass dominance. 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 Landmark XP (50 % sulfometuron methyl + 25% chlorsulfuron +25% inert material) @1.75 oz/acre rate in the fall of 2015, fallowed the site for 1-year and seeded desirable native and introduced perennial grasses using a Kincaid no-till drill. The herbicide application resulted in more than 98% cheatgrass control which significantly increased available mineral nitrogen and soil moisture for seeddlings of seeded species. Perennial grass establishment into the second-year averaged 3.3/ft² in the introduced and native 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.

Technical Abstract: One of the greatest environmental challenges of the 21st century is cheatgrass invasion on western rangelands, resulting in the recurrence of catastrophic wildfires. With each passing wildfire season, more and more critical habitats are being converted from productive landscapes to cheatgrass dominance. In 2017, Nevada had over 600 individual wildfires, burning a total of 1.2 million acres. In an effort to minimize the negative effects of wildfires, 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 associated fine fuels. Using the pre-emergent herbicide, Landmark XP @ 1.75 oz/acre rate, fallowing the site for 1-year and seeding with a variety of native and introduced seed mixes we recorded > 98% cheatgrass control in the herbicide plots and an increase of perennial grasses from 47/acre to 120,000/acre. We recorded a 16-fold increase in available mineral nitrogen and a 3-fold increase in available soil moisture at the seedling stage of the seeded perennial grasses. The germination, emergence and establishment of perennial grasses decreased cheatgrass densities and associated fuels by more than 96%.