DOI: 10.5061/dryad.hdr7sqvgz
title: Herbicide effects on the establishment of a native bunchgrass in annual grass invaded areas: Indaziflam vs. imazapic

description: Annual grass invasion is transforming the western US and driving a need
 for restoration techniques that can both reduce exotic annual grass
 abundance and allow revegetation of native species. Pre-emergent
 herbicides can provide control of annual grasses, but when applied
 concurrently with direct seeding efforts, the herbicide can also impact
 seeded species. Indaziflam is a relatively new herbicide that may provide
 extended control of exotic annual grasses, but little is known about its
 effects when applied at the time of seeding.  In this study, we
 compared indaziflam to imazapic, a popular herbicide used in restoration
 efforts, to understand how indaziflam affects plant establishment of a
 native species, bluebunch wheatgrass Pseudoroegneria spicata (Pursh) Á.
 Löve. We created furrows on half our treatments to limit herbicide
 concentrations and potentially create a safe-site for seeding bluebunch
 wheatgrass.  During the two-year study, indaziflam provided
 consistent control of the annual weed, downy brome Bromus tectorum L.,
 whereas imazapic control decreased sharply with time. Indaziflam and
 imazapic decreased bluebunch wheatgrass seedling emergence by 96 and 46%,
 and two-year plant density by 91 and 65%, respectively, compared to
 non-herbicide treatments. Both herbicides reduced aboveground biomass of
 bluebunch wheatgrass by over 85% two years after seeding/herbicide
 application.  Furrow treatments mitigated imazapic effect on
 bluebunch wheatgrass, but did not limit the impacts by
 indaziflam.  Herbicide can be used in conjunction with direct
 seeding efforts, but mitigation of the effects to native seeds will depend
 on herbicide specifics such as mode of action and soil mobility. 
description: <i>Plant
 Measurements</i> Bluebunch wheatgrass seedling
 emergence was characterized at the end of April 2018 by individually
 counting all live seedlings in each row of the entire plot. Bluebunch
 wheatgrass aboveground biomass was sampled and dried in late August 2019,
 two years after the initial planting. Biomass samples were collected by
 clipping all aboveground biomass at ground level. Downy brome cover was
 measured visually during the last week of May 2018 and May 2019. Bluebunch
 wheatgrass density was counted simultaneously as biomass was destructively
 sampled. Both bluebunch wheatgrass plant density and aboveground biomass
 were sampled once, 2 years after planting. All bluebunch wheatgrass
 sampling was done on the center row of three side-by-side replicate rows
 to limit edge effect. Downy brome cover estimates were
 made visually to the nearest 1% using a circular metal hoop (Bonham et
 al., 2004). The hoop used was 1 m in diameter and placed over three
 side-by-side rows of the same treatment. Percent of total ground area
 occupied by downy brome within the hoop was estimated visually using the
 total hoop area to the nearest percent. These hoops were placed in the
 same position during both years of the study. Downy brome cover values
 were estimated for each treatment (4 per sub-block) averaged to the
 sub-block level, such that each herbicide treatment had one statistical
 repetition at the block level.