Performance of the pre-emergent herbicide indaziflam on cheatgrass rangelands

Authors: Clements, Darin - Charlie; QUICKE, HARRY - Bayer Cropscience; Harmon, Daniel - Dan

Submitted to: The Progressive Rancher
Publication Type: Popular Publication
Publication Acceptance Date: 10/20/2022
Publication Date: 11/14/2022
Citation: Clements, D.D., Quicke, H., Harmon, D.N. 2022. Performance of the pre-emergent herbicide indaziflam on cheatgrass rangelands. The Progressive Rancher. 22(8):12-13.

Interpretive Summary:

Technical Abstract: Resource managers are constantly looking for effective tools to restore or rehabilitate degraded habitats. Throughout the Intermountain West, the accidental and subsequent invasion of cheatgrass has converted former big sagebrush/bunchgrass habitats into annual dominance, especially cheatgrass. Cheatgrass competition on rangelands is a major issue as cheatgrass outcompetes desirable perennial species at the seedling stage for limited resources. Mechanical and chemical treatments to reduce cheatgrass densities and associated fuels have been conducted and reported with varying degrees of success. Chemical, herbicide, use on rangelands to reduce cheatgrass densities and associated fuels is increasing in popularity, especially soil-active, pre-emergent herbicides. Imazapic (Plateau) is the most common pre-emergent herbicide used on cheatgrass-infested rangelands. Treated sites are recommended to be applied in late summer/early fall prior to any effective moisture that can trigger fall cheatgrass germination and emergence, that is why they are called pre-emergent herbicides. Application of pre-emergent herbicides in late fall may very well end up in a less than optimal control of cheatgrass that is necessary in the restoration/rehabilitation seeding efforts. A more recent herbicide that has introduced itself into the conversation of cheatgrass control is Indaziflam. Indaziflam is a broad-spectrum pre-emergent herbicide that was first released in 2011 for use in several perennial cropping systems. In 2016, a supplemental label for Indaziflam was approved for release for the restoration of natural areas as well as fire rehabilitation areas, and more specifically to target winter annual grasses such as cheatgrass. Currently, the Indaziflam product registered for use on rangelands is Rejuvra, at a recommended rate of 5 oz/acre. Indaziflam controlled cheatgrass densities from 36.8-98.6% compared to Imazapic, 94.2-97.8%. Imazapic treated plots resulted in significantly more perennial grass seedling emergence and establsihment than Indaziflam treated plots. Although Indaziflam has longer lasting residue activity that appears to have negative affects on seedlings of seeded perennial grasses compared to Imazapic, we have also witnessed the benefits of this longer lasting activity on cheatgrass control and perennial grass performance. When Indaziflam was applied over exiting perennial grasses, the control of cheatgrass in the community was nearly complete, 98.6%, and the perennial grasses increased in vigor due to the increase in available moisture and nitrogen that the cheatgrass and other weeds were utilizing. At this point, we have not concluded that Indaziflam is effective at controlling cheatgrass and rehabilitating the site back to perennial grasses in the short-term, but the use of Indaziflam on exiting intact herbaceous communities or greenstrips would provide added benefits to improve stand vigor, improve maintenance of greenstrips and decrease the fine fuels associated with cheatgrass, therefor decreasing the chance, rate, spread and season of wildfires that are so destructive to Great Basin rangelands.