Cultural Methods for the Control of the Invasive Japanese Stiltgrass (Microstegium vimineum) in Stream Restoration

Microstegium vimineum (Japanese stiltgrass) is one of the most invasive plant species in the eastern United States, posing a consistent problem to practitioners working in stream restoration and often necessitating treatment using non-selective herbicides to reduce invasion. Herbicide use frequently results in collateral damage to desirable native species and can lead to reinvasion after treatment. This study evaluated alternatives to herbicide referred to collectively as cultural controls, the use of which draws conceptually from the interaction of stress and disturbance in plant communities that predicts reduced invasion and increased competitive success of native species with higher levels of environmental stress. We tested several preventative cultural approaches, including (intended stressor in parentheses): (1) canopy shade (light limitation), (2) sawdust soil amendments (short-term nitrogen limitation), (3) wood mulch soil amendments (longer-term nitrogen limitation), and (4) double seeding rates (native species competition), as well as a combination of these treatments. Over a two-year field study within a restored stream corridor, we found that high carbon: nitrogen ratio soil amendments such as sawdust were the most effective at attenuating M. vimineum invasion and that shade promoted native species competition with this invader. Our results suggest a set of best practices that stream restoration practitioners could consider during the design and construction phases of a stream restoration project, particularly on sites with increased risk of M. vimineum incursion.