Enhanced Precision of Aerial Herbicide Application for Invasive Species Management

Abstract

Invasive common reed (Phragmites australis ssp. australis) has established and dominated in Ontario wetlands for decades. The detrimental effects of P. australis invasions on wetland habitats have demanded intervention through aggressive suppression efforts. However, constraints in available control methods to suppress P. australis have led to persistence. To improve P. australis management in wetlands, we investigated remotely piloted aircraft systems (RPASs) as a precision tool for herbicide application. We applied Habitat® Aqua with a spray-equipped RPAS at selected pilot sites, marking the first-ever application of its kind in Canada. We evaluated the suppression efficacy of RPAS-based herbicide application to P. australis and examined the plant community changes one-year after the initial herbicide application. We found a > 99% reduction in live P. australis stems, along with reductions in species richness (33%), Shannon-Weiner diversity (73%), Simpson’s reciprocal diversity (50%), and Pielou’s evenness (73%) in the year following herbicide application. We performed an in-field application experiment to quantify the herbicide deposition of an RPAS-based application through the vertical profile of a P. australis canopy, comparing medium and coarse droplet sizes. We determined that both droplet sizes achieved similar coverage and vertical penetration of herbicide within the P. australis canopy. Lateral droplet drift occurred at least 8 m away from the application area with medium droplets diminishing at a faster rate than the coarse droplets. We used remotely-sensed images taken before and after the RPAS-based herbicide application to determine the application accuracy and post-treatment effects. We determined that RPAS-based herbicide application to P. australis was on-target 91% of the time. The herbicide drift footprint extended up to 20 m away from the application area, representing a distance that is 96% lower than the label-recommended buffer distance for Habitat® Aqua application with a helicopter.