Managing Reed Canary Grass in Wetlands with Minimal Environmental Impact

Reed canary grass (Phalaris arundinacea) is a ubiquitous plant species that degrades wetlands by forming monocultures throughout the Pacific Northwest. Applications of glyphosate-based pesticides are effective and commonly applied at a rate of 2% with an appropriate surfactant for the management of reed canary grass. However, the use of glyphosate has become controversial in recent years over concerns of the potential harm to humans, native vegetation and freshwater ecosystems. Additionally, the costs and time required to effectively manage reed canary grass continue to increase placing additional pressure on project budgets. This study assesses the effectiveness of various applications of glyphosate-based pesticide formulations in managing reed canary grass populations using high resolution multispectral imagery acquired with unmanned aerial systems. A set of six glyphosate-based formulations ranging from 0.5% to 2% with and without a water buffering agent, or kicker, were tested in a complete randomized design with five replications at Jackson Bottom in Hillsboro, OR. The images were captured biweekly during the growing season from April 2019 to October 2020, leading to 29 orthoimages. Repeated measures analysis suggests no significant difference between the highest (2%) and lowest (0.5%) glyphosate concentrations tested in managing reed canary grass, indicating that each concentration is equally effective. Moreover, we found that the kicker provided no significant contribution in managing reed canary grass. Therefore, to reduce the potential harm to humans, native vegetation and freshwater ecosystems while controlling treatment costs, we suggest using minimal concentrations of glyphosate with appropriate adjuvants when managing reed canary grass.