Optimizing Use of Herbicides and Surfactants for Control of Two Midwest Forest Invaders: Amur Honeysuckle and Wintercreeper

Amur honeysuckle (Lonicera maackii (Rupr.) Herder) and wintercreeper (Euonymus fortunei (Turcz.) Hand.-Maz.) are important invasive plants in Midwestern U.S. forests. We studied how two herbicides at two concentrations combined with three concentrations of a surfactant affected the mortality of these species. For L. maackii, we also studied the effect of application timing, and for E. fortunei, we also measured the treatment effect on native species after one year. For E. fortunei, triclopyr caused complete mortality at both low and high concentrations. The application of glyphosate increased mortality from low to high concentrations. The addition of a surfactant to glyphosate increased mortality, with the low concentration being as effective as the high concentration. There was a negative effect of surfactant on native species, with the high concentration of the surfactant causing a 75% reduction in native species compared to not using a surfactant. For L. maackii, there was greater mortality from the fall application of herbicides. Mortality was higher overall with the addition of a surfactant, but the effect of the surfactant was more important in spring. Glyphosate was more effective in fall, while triclopyr tended to be more effective in spring. Generally, lower concentrations of herbicides tended to have a higher efficacy in the fall. Our results can help managers determine the best method of chemical control that balances cost, efficacy, and recovery of native species.