Perennial grass establishment following fall and spring imazapic applications

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

Submitted to: Society for Range Management
Publication Type: Abstract Only
Publication Acceptance Date: 12/21/2020
Publication Date: 2/16/2021
Citation: Clements, D.D., Harmon, D.N. 2021. Perennial grass establishment following fall and spring imazapic applications. Society for Range Management. 74:60.

Interpretive Summary:

Technical Abstract: It is critically important that land managers have useful information available to them when attempting proper weed control practices in efforts to improve restoration/rehabilitation efforts on cheatgrass-infested rangelands. We were approached on the topic of applying the well known pre-emergent herbicide, Imazapic, in the spring of the year on cheatgrass-infested rangelands and then seeding that treated habitat the following fall. Our experience has been that Imazapic has a soil activity of 12-15 months and the residual activity could damage seeded species seedlings and decrease overall establishment of seeded species. We initiated an experiment by which we applied Imazapic in the fall of 2017 and the spring of 2018 @ 70g ai/ha (6oz/ac). The treated plots were seeded in the fall of 2018 with introduced, native and introduced/native perennial grass seed mixes using a no-till drill. Establishment of perennial grasses in each seed mix was significantly higher in Imazapic fall treated plots. Fall plots recorded 21.5, 8.6 and 17.2 perennial grasses/m² in the introduced, native and introduced/native seed mixes respectfully. Imazapic spring treated plots recorded 7.5, 3.2 and 7.5 perennial grasses/m² in the same seed mixes, respectfully. The Imazapic spring treated plots continued to show cheatgrass control in the spring of 2019, 1 year following application which is another indicator that this non-selective, soil-active pre-emergent herbicide has the residual effect to cause additional mortality to seedlings of seeded species. The cold desert environments of northern Nevada rangelands receive the vast majority of its’ precipitation during the winter months, spring applications of Imazapic in environments that receive warm season precipitation may experience less perennial grass mortality than cold desert environments of northern Nevada.