Control of invasive plants at high latitudes with persistent herbicides: understanding persistence, to manage pesticide residues and achieve effective control

Abstract

Invasive plants are considered a problem in management of natural resources and maintenance of ecosystem services in Alaska. Persistent herbicides are often used to control invasive plants because of increased duration and efficacy of control; however, applicators must understand that persistence impacts rotations to sensitive crops or restoration to sensitive desirable species. The purpose of this study was to define and document the impacts of aminopyralid and clopyralid degradation and movement in boreal ecosystems when used in agricultural settings or applied to Prunus padus, a problematic invasive tree in the boreal ecosystem. In laboratory microcosms clopyralid did not adsorb to soil particles under any conditions. Aminopyralid adsorbed to soil particles with increased adsorption at lower pH due to protonation of the amine group. Amnopyralid and clopyralid were compared in agricultural field treatments of fallow ground, followed by two years of small grain production before rotation to field peas, a sensitive species in the third year. Herbicide was detected one year after treatment with both herbicides, but by two years after treatment only aminopyralid was detectable in soil. Bioassays performed with these same soils had a similar pattern with smaller plants 1 and 2 years after treatment, but no indication of herbicide 3 years after treatment. Despite the lack of detection in soils, herbicide sensitive field peas were unable to grow in aminopyralid treated plots 3 years after treatment, indicating the presence of biologically significant concentrations of herbicide. Aminopyralid applied to stems of invasive Prunus padus saplings was exuded from the roots of treated trees, with herbicide detected in soils and resulting in damage to some susceptible species. Applications of triclopyr resulted in the detections of herbicide and observations of non-target damage without significant change in defoliation of the target trees. Reduced rates were equally effective for aminopyralid.