Leafy spurge (Euphorbia virgata) is an invasive weed that can lead to declines in plant diversity, forage productivity and grassland ecosystem functioning. Herbicides are frequently used to control leafy spurge but can also negatively affect ecosystem functioning through impacts on non-target species and consequent shifts in plant and microbial communities. Given the spread of leafy spurge and thus increased use of herbicides, better understanding of repeated herbicide use is necessary, lest the cure be worse than the disease. In 2020, we established an experiment in a leafy spurge invaded mixed grass prairie in Saskatchewan to test the effects of three herbicide treatments – an untreated control, a single herbicide application and an annual application – on both invaded and uninvaded plots. In 2020 and 2021, after all treatments were complete, we collected plant and soil samples to measure leafy spurge abundance, plant community composition, forage productivity, soil bacterial and fungal abundance and community composition, and soil carbon and nitrogen retention to determine whether herbicide use can sustainably control leafy spurge and enhance forage production, while maintaining grassland and soil health.
Results/Conclusions
Our preliminary results showed that both herbicide treatments reduced leafy spurge biomass and density as well as broadleaf plant species biomass and richness, which was more greatly reduced in the annual treatment than the single application. This suggests that multiple applications may be even more detrimental to non-target species. There was also no increase in forage biomass in either treatment. Total soil carbon and nitrogen and plant available nitrogen were unaffected by the herbicide treatments. Plots invaded by leafy spurge had reduced forage productivity, while carbon and nitrogen were unaffected. Our preliminary results therefore suggest that herbicide application may have limited impact on ecosystem function; however, longer term effects or effects on other ecosystem components, such as changes to microbial communities, remain possible.
