Evaluating winter annual grass control and native species establishment following applications of indaziflam on rangeland

Abstract

Indaziflam, a preemergent (PRE) herbicide option for weed management on rangeland and natural areas, provides long-term control of invasive winter annual grasses (IWAGs). Since indaziflam only provides PRE control of IWAGs, postemergent (POST) herbicides such as glyphosate can be mixed with indaziflam to control germinated IWAG seedlings. Field trials were conducted at three sites on the Colorado Front Range to evaluate glyphosate dose required to provide adequate POST IWAG control, and compare long-term Bromus tectorum L., Bromus japonicus Houtt. and Secale cereale L. control with indaziflam and imazapic. Two of the three sites were void of desirable species and so species establishment through drill seeding was assessed, while the remnant native plant response was assessed at the third site. Herbicide applications were made March 2014 through April 2015, and two sites were drill seeded with native species nine months after herbicide application. Yearly visual control evaluations, biomass of all plant species, and drilled species stand counts were collected. Glyphosate at 474 g ae ha-1 reduced B. tectorum biomass to zero, while glyphosate at 631 g ae ha-1 was needed to reduce biomass to near zero at the S. cereale site. At all three sites, only indaziflam treatments had significant reductions in IWAG biomass compared to the non-treated check at 3 years after treatment (YAT). By 3 YAT in the drill seeded sites, cool-season grass frequency ranged from 37 to 69% within indaziflam treatments (73 and 102 g ai ha-1) while imazapic treatments ranged from 0 to 26% cool-season grass frequency. In the site with a remnant native plant community, indaziflam treatments resulted in a three- to four-fold increase in native grass biomass. These results indicate that the multi-year IWAG control provided by indaziflam can aid in desirable species re-establishment through drill seeding or response of the remnant plant community.

Indaziflam controls nonnative Alyssum spp. but negatively affects native forbs in sagebrush steppe

“…Established perennial graminoid richness and Shannon's diversity were largely unaffected by indaziflam (P = 0.96 and P = 0.50, respectively) (Tables 2 and 3, Supplementary Figure S1), as expected from previous studies (Clark et al 2019(Clark et al , 2020. Perennial forb mean species richness was lower in sprayed plots (P < 0.01) and under high invasion (P = 0.02), decreased with elevation (P < 0.01), and differed between years (P = 0.01; Table 3, Supplementary Figure S1).…”

“…In areas where the seedbank is composed mostly of nonnative species that have formed persistent soil seedbanks, indaziflam is a valuable tool to deplete the seedbank of target species before active revegetation efforts (Clark et al 2020). However, in areas with minimal infestations, an existing diverse plant community, and therefore likely a diverse seedbank, the use of indaziflam and its impacts on the seedbank of nontarget species should be carefully considered before broadscale use.…”

“…The preemergent herbicide indaziflam is promoted as an option to control invasive annual grasses in sagebrush steppe (Clark et al 2020;Sebastian et al 2016). Indaziflam is a nonselective herbicide that inhibits cellulose biosynthesis (Brabham et al 2014) and provides residual control in the top few centimeters of soil (0 to 2.5 cm).…”

Herbicide effects on the establishment of a native bunchgrass in annual grass invaded areas: Indaziflam versus imazapic

“…Another option would be to wait (2–5 years) until the indaziflam activity level has decreased, and then seed native species. One study showed success seeding in the fall following a spring application of indaziflam (Clark et al., 2020). Both approaches could potentially lead to restoration seeding success, and long‐term invasive annual grass control, but waiting to seed several years after herbicide application could potentially result in large areas of bare ground and eventual erosion on sloped or high wind areas.…”

“…Some studies have compared invasive annual grass control by herbicide (Applestein, Germino, & Fisk, 2018; Clements, Harmon, Blank, & Weltz, 2017; Elseroad & Rudd, 2011; Sebastian, Nissen, Sebastian, Meiman, & Beck, 2017b), but few have examined potential ways to control invasive annual grasses while simultaneously allowing seeding of native species that are also susceptible to herbicide (Clark, Sebastian, Nissen, & Sebastian, 2020; Eckert et al., 1974). Here we study two herbicides that differ in mode of action, soil persistence, and soil mobility to identify potential strategies that control invasive grasses without harming native species seeded for restoration.…”