The bioherbicide Verticllium nonalfalfae effectively removes Ailanthus altissima but leaves many other nonnative plants

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Abstract Ailanthus altissima (Mill.) Swingle readily exploits disturbances, grows quickly into dense monocultures, and suppresses native plant species. The vascular wilt pathogen, Verticillium nonalfalfae Inderb., native to the eastern U.S., has been proposed as a biocontrol agent for the invasive A. altissima. Studies consistently demonstrate the safety and efficacy of the bioherbicide, but they also note that the selective nature of the fungus does not preclude other invasive plants that commonly co-occur with A. altissima from occupying the site. We quantified the standing plant community and seedbank at several sites across Virginia five years after inoculation with V. nonalfalfae to understand which species are present or being naturally recruited. A. altissima remained dominant in untreated areas but was nearly eradicated from the treatment plots. Other nonnative species made up a large portion of the plant community and seedbank across all study areas, with no differences in their respective cover and count between treatments. While variability in plant community composition is high and site-specific context is important for establishing effective management strategies, planting native species and mitigating other invasives will be crucial to ensuring native species successfully establish in bioherbicide-treated areas.