Fungal suppression as a means to control leafy spurge and restore range health

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Leafy spurge (Euphorbia esula) is a widespread invasive plant that has infested nearly two million hectares of land in North America, with costs projected to exceed a billion dollars in Canada alone. Many of these effects derive from the fact that leafy spurge forms large monocultures that reduce biodiversity and forage for livestock. Because leafy spurge produces extensive rhizomes and abundant seed, it can recover rapidly from disturbance and is difficult to control. However, leafy spurge is reliant on symbiotic soil fungi (mycorrhizal fungi) for nutrients: disrupting these symbioses with fungicide may allow resident vegetation to recover in invaded areas. Recovery of the resident vegetation may also be enhanced by defoliating leafy spurge - which would reduce shading - and by reseeding resident species that do not rely on mycorrhizal fungi for soil nutrients. The proposed research evaluates fungicide as a control measure for leafy spurge, by establishing an experiment suppressing fungi, defoliating leafy spurge using herbicide and mowing, and reseeding native plants. This experiment will be distributed across 24 native grassland sites spanning the range of leafy spurge invasion in Saskatchewan. Within the experiment, we will monitor effects on leafy spurge populations as well as the structure, abundance, and nutritive value of the native plant community. These data will be used to evaluate the efficacy of the proposed control measures, and will be combined with local environment measurements to identify which conditions facilitate leafy spurge control and vegetation recovery. Additionally, to evaluate treatment effects on plant-soil interactions, we will combine these results with measurements of microbial colonization of leafy spurge roots and soil microbial community structure. This project will increase our understanding of the effects of leafy spurge invasion in general, and in Saskatchewan in particular. Further, we will use these results to develop context dependent recommendations for leafy spurge control, including which native species can be reseeded to suppress leafy spurge.