Evaluating the efficacy of removal treatments on wavyleaf basketgrass (Oplismenus undulatifolius)

With the spread of a new invasive plant species, it is vital to determine the effectiveness of removal strategies as well as their advantages and disadvantages before attempting widespread removal. While thousands of dollars have been spent to curtail the spread of wavyleaf basketgrass [Oplismenus undulatifolius (Ard.) P. Beauv.], a relatively new invasive species, the lack of a cohesive management plan and funding has made controlling this species especially difficult. We assessed the efficacy of a variety of chemical control methods and hand weeding for this species and followed select methods over time. We also assessed the potential for ecosystem recovery following removal by measuring total and native species richness in response to treatments. Our pilot study revealed a wide breadth of responses to our eight herbicides, with fluazifop plus fenoxaprop, imazapic, quizalofop, and sulfometuron methyl being the least effective. In our follow-up experiments, hand weeding, glyphosate, and clethodim treatments were effective at reducing O. undulatifolius percent cover, density, and biomass, with an average reduction of at least 48% in the first year. However, we found substantial variation in the effectiveness of clethodim between our two experiments, which was likely driven by site differences. We also found that all three of these removal methods were effective at reducing the number of O. undulatifolius flowering stems and the height of those stems, which will likely reduce the spread of this species to new areas. Finally, we found that these methods have the potential to restore total and native species richness, but that glyphosate-treated plots did not fully recover until 2 yr after treatment.

Interspecific competitive potential of wavyleaf basketgrass (Oplismenus undulatifolius), a recent introduction to the mid-Atlantic United States

Understanding the mechanisms by which an invasive plant species is able to colonize and successfully expand into native plant communities can help in estimating the potential threat posed by a new invader and predict impacts on community diversity, structure, and function. Wavyleaf basketgrass [Oplismenus undulatifolius (Ard.) P. Beauv.] is a perennial, shade-tolerant grass species that has been recently introduced to the mid-Atlantic United States. Areas invaded by O. undulatifolius typically have low species richness, but it is unknown whether O. undulatifoius actively outcompetes other species or simply thrives primarily in species-poor habitats. This study used a greenhouse experiment to quantify interspecific competition in shade and sun among seedlings of O. undulatifolius; Japanese stiltgrass [Microstegium vimineum (Trin.) A. Camus], an invasive annual grass common in the region; and a mix of three native perennial grass species commonly used in restoring areas invaded by M. vimineum. In this experiment, shade did not significantly affect growth or competitive ability. Interspecific competition irrespective of shade had a negative effect on growth of all species, but O. undulatifolius was affected to a much greater degree than either M. vimineum or the native grass mix. These results suggest that, at least under these conditions, O. undulatifolius is a weak interspecific competitor and may be capable of forming dense monotypic stands only in areas that already have low species diversity. In the mid-Atlantic region, postagricultural legacies and overabundant deer populations, which lead to depauperate understories, may be a major facilitator of O. undulatifolius invasion in forests.