Chemical control of downy brome (Bromus tectorum) is one of the primary tools employed to restore degraded rangelands in Western North America. However, many herbicides used to control downy brome may also inadvertently inhibit germination of desirable seeds planted following chemical treatment. We evaluated three herbicides: Imazapic (Plateau®), Indaziflam (Esplanade®), Rimsulfuron (Matrix®) and Indaziflam/Rimsulfuron in combination. We compared each product’s ability to control downy brome over multiple (2) years, as well as the unintended inhibition of seeded species in treated areas one or two years after chemical application. Six common restoration species (bluebunch wheatgrass, Siberian wheatgrass, blue flax, alfalfa, Wyoming big sagebrush, and forage kochia) were seeded into treatment areas either the same year as herbicide application (single entry), one year following herbicide application (multiple entry), or immediately prior to herbicide application (sprayed after seeding). Downy brome cover and density of seeded species within each treatment was measured the following spring.
Results/Conclusions
While Indaziflam consistently achieved the highest and most consistent control of downy brome in both the single and multiple entry treatments—especially when used in combination with Rimsulfuron—it substantially inhibited emergence of all seeded species, even two years (multiple entry) after chemical application. Imazapic achieved moderate control of downy brome in the single entry treatment, but control was not maintained in the multiple entry treatment. However, Imazapic also had the least severe inhibition on emergence of seeded species in the single entry treatment, and was similar to Rimsulfuron in the multiple entry treatment. Rimsulfuron achieved the highest control of downy brome in single entry treatments of individual herbicides, but with a corresponding high inhibition of seeded species. Rimsulfuron had similar control and inhibition on seeded species as Imazapic within the multiple entry treatment, but with some differentiation in control and inhibition among sites and species, respectively.