Introduction

Background

Invasion of annual brome grasses has been a major problem in rangelands of the western United States, threatening the multifunctionality of rangeland ecosystems that provide a variety of ecosystem goods and services including forage, biodiversity, wildlife habitat, and carbon sequestration. Their invasion progressively reduces the diversity of native plant communities, reduces the availability of quality forage, changes seasonal patterns of forage production, and can ultimately negatively impact livestock performance (Haferkamp 2001). Aberration from the native plant community also negatively impacts rangeland wildlife and their access to food and habitat (Bachen et al. 2018). Further, rangelands invaded by annual bromes are more susceptible to wildfire (Balch et al. 2013), posing risk to public safety, wildlife, livestock, and rangeland health.

Compared to the western US, Alberta and western Canada have experienced relatively little annual brome invasion to date (Douglas et al. 1990; Leeson et al. 2017). This has been changing however, and recently increases in annual bromes along the US-Canada border have been observed, leading to concerns about Albertan grassland conservation (communication with landowners; Leeson et al. 2017). Due to the relatively recent onset of brome expansion into Alberta grasslands, early control action may be a valuable tool to provide containment of the invasion within southern Alberta.

The herbicide indaziflam has recently shown promise in controlling annual grasses on western US rangeland (Clark et al. 2019; Sebastian et al. 2016; Sebastian et al. 2017). Indaziflam is a pre-emergent, non-selective, cellulose biosynthesis inhibiting herbicide that has demonstrated long residual activity in the soil, causing ongoing seedling mortality capable of depleting the annual brome seed bank over time while potentially having little negative impact to native perennial species (Sebastian et al. 2016; Sebastian et al. 2017). However, Alberta’s agroclimatic conditions (i.e. climate, soil, veg) are markedly different than the midwestern US plains. Since residual activity of indaziflam is dependent on precipitation and soil properties (Alonso et al. 2011; Sebastian 2015), the herbicide should be tested within Alberta’s agroclimatic conditions.

Research Objectives

The objectives of this research are to assess the efficacy of indaziflam in controlling annual brome grass in the dry mixed grass prairie of Alberta and to determine how indaziflam affects native plant composition and production. Specific study objectives are to:

1) Compare indaziflam control of annual bromegrass following its application at two different times of the year and three different herbicide rates by measuring annual bromegrass cover one year, two years, and three years after treatment.

2) Assess the impacts of indaziflam on non-target vegetation cover one year, two years, and three years after treatment.

We hope to determine whether indaziflam effectively controls annual bromegrass in Alberta, and what the best rate and timing of application would be to do so. The results will also help in identifying potential drawbacks of using this herbicide, such as non-target effects to native species. Ultimately, we hope to provide information that will help land managers decide whether it makes sense to use this herbicide based on their environmental and economical goals for the land.