Suppression efficacy of remotely piloted aircraft systems-based herbicide application on invasive Phragmites australis in wetlands

Abstract

Invasive common reed [Phragmites australis (Cav.) Trin. ex Steud. ssp. australis] has established and dominated 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 persistent invasions. To improve P. australis management in wetlands, we investigated remotely piloted aircraft systems (RPASs) as a precision tool for herbicide application. We applied an imazapyr-based herbicide (240 g ai L-1) with a spray-equipped RPAS at selected test sites, marking the first-ever application of its kind in Canada. We then (1) evaluated the efficacy of RPAS-based herbicide application to P. australis and (2) examined the plant community changes 1 yr 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. Plant community changes varied by field site; one wetland underwent a secondary invasion by European frog-bit (Hydrocharis morsus-ranae L.) while the other was dominated by the native spotted jewelweed (Impatiens capensis Meerb.), highlighting the complexities of plant community succession following herbicide application in biodiverse wetlands.