Legacies of invasive plant management: effects of leaching from glyphosate-treated and untreated plants on germination and early growth of native macrophytes

Invasive plant management can support the restoration of native plant communities. Glyphosate-based herbicides are commonly used for management because glyphosate does not persist at toxic concentrations in water and soil; however, glyphosate can accumulate in the tissues of treated plants. This study investigated whether glyphosate-treated plants can release glyphosate in their leachate, and if so, whether leachate from glyphosate-treated versus untreated plants affects the germination and seedling growth of native plants. We sprayed industry-standard concentrations of glyphosate (Roundup WeatherMAX®) on two macrophyte taxa that are invasive in North America: Phragmites australis and Typha × glauca . Nine weeks after spraying, we submerged sprayed and unsprayed plant tissues in water to create leachate. We quantified glyphosate and the degradation product aminomethylphosphonic acid (AMPA) in leachate over 21 days, and assessed the effects of leachate from sprayed and unsprayed plants on the germination and growth of two co-occurring native macrophytes, Typha latifolia and Ammannia robusta . Leachate from both treated invasive plant taxa contained glyphosate and AMPA, with P. australis leaching more glyphosate on average than T. × glauca . Typha latifolia germination and growth was stimulated by leachate with and without glyphosate. Ammannia robusta exhibited mixed responses, with some indication that leachate and glyphosate residues exert temporary inhibitory effects. Our study demonstrated that glyphosate-sprayed plants can release glyphosate into the environment, but negative impacts from this leachate on the germination and growth of at least some native macrophytes are short-term (