Plant invasions have far-reaching consequences that affect humans and ecological systems. A potential invader switches from being a minor component of its native community to a major component in its invaded community, displacing native species and threatening biodiversity. Bromus tectorum long-term dominance in western rangelands has been associated with a loss of desired perennial species' seedbank and recruitment, which may be due to soil pathogens. A soil-borne generalist fungal pathogen, Pyrenophora semeniperda, is able to kill B. tectorum seeds in the seedbank, providing the missing link to current management strategies that only target B. tectorum seedlings. Accordingly, our objective was to assess the potential of improving B. tectorum management by integrating an herbicide, imazapic, and P. semeniperda, with varying rates of perennial grass seeding and a fungicide seed treatment. We applied this ecologically based management strategy to a randomized complete block field experiment, with four replications, which was followed for two years. Vegetation density was recorded every year and biomass was collected the second year. Bromus tectorum seeds were retrieved from soil samples to assess P. semeniperda abundance and seeds were scored as infected or non-infected.
Results/Conclusions
Plots inoculated with P. semeniperda did not differ in infection from those that weren't (22.1 ± 3.6%, 20.9 ± 3.3%, respectively) (P = 0.88). Consequently, we pooled across the P. semeniperda treatment for a repeated measures analysis of variance and an analysis of variance to assess treatment effects on density and biomass, respectively. There was no effect of fungicide or seeding rate; however, herbicide affected B. tectorum and seeded perennial grass density. Bromus tectorum density in Year 1 was higher in non-sprayed (1382 ± 518 tillers m-2) compared to sprayed (576 ± 312 tillers m-2) plots; the effect disappeared in Year 2 when both had similar densities. Seeded perennial grass density was twice as great in sprayed (25 ± 7 tillers m-1) compared to non-sprayed plots (13 ± 6 tillers m-1). Biomass was unaffected by treatments. Although P. semeniperda was ineffective, we controlled B. tectorum for one year with a single herbicide application and had strong perennial grass establishment two years post treatment. Utilizing a biocontrol agent for B. tectorum requires further research on how to increase its abundance beyond ambient levels. Overall, multi-pronged approaches (e.g. herbicides and revegetation) will better serve the West in maintaining biodiversity and ecosystem services.