Integrating the herbicide imazapic and the fungal pathogen Pyrenophora semeniperda to control Bromus tectorum

Bromus tectorum is a winter annual grass that affects rangeland in western North America. A glasshouse pot experiment was conducted that integrated imazapic application and inoculation of the soil-borne fungal pathogen, Pyrenophora semeniperda, for the purpose of providing greater control of B. tectorum. We hypothesised that P. semeniperda inoculation would reduce B. tectorum emergence and integration of imazapic and P. semeniperda would result in a greater reduction in B. tectorum biomass and density compared with either treatment applied alone. This study revealed that P. semeniperda significantly reduced B. tectorum emergence and density and the responses were greatest for seed placed below the soil surface. Further, B. tectorum biomass was similar between imazapic and P. semeniperda treatments. This indicates that P. semeniperda could be applied in advance of B. tectorum germination and emergence. After emergence, imazapic application could reduce B. tectorum biomass and kill seedlings. A two-pronged approach to controlling B. tectorum that combines P. semeniperda inoculation and post-emergent imazapic application may provide a greater opportunity to limit invasion of this weed in rangeland of western North America. Future work should be directed towards the pathogen-plant relationship and how it relates to integrating biological control with traditional methods, towards the effect of varying P. semeniperda inoculum and imazapic rates and lastly, to how environmental conditions in the field may affect implementation and efficacy of this two-pronged approach.