Herbicides in Unexpected Places: Non-Target Impacts from Tree Root Exudation of Aminopyralid and Triclopyr Following Basal Bark Treatments of Invasive Chokecherry (Prunus padus) in Alaska

Abstract

Abstract Basal bark treatment of invasive trees is an approach designed to limit damage to non-target vegetation in the vicinity, but non-target injury is still documented. No study of basal bark treatments has examined the release of herbicide residues from roots of treated plants and resulting non-target impacts. Studies were conducted in Alaska interior and coastal boreal forests on basal bark treatments with aminopyralid and triclopyr on active-growth and dormant invasive chokecherry (Prunus padus L.). The study assessed non-target damage and soil herbicide residue using a combination of visual evaluations, bioassays, and soil residue analyses. Non-target damage from herbicide residues were identified in 40% of treatments containing aminopyralid with triclopyr, 60% of treatments containing aminopyralid alone, and 5% of treatments containing only triclopyr. Laboratory studies of aminopyralid treatments to saplings isolated the effects of herbicide exudation from roots, which was found to be significant, and the magnitude was dependent on dose. Herbicide soil residues in field and laboratory experiments were quantified with analytical detection and plant bioassays. Aminopyralid soil residues were identified in 57% of field treatments receiving 8 to 60 ml of herbicide solution (2% ai) and 70% of laboratory treatments receiving 10 µl of herbicide solution (2% to 16% ai). Triclopyr residues were found from one field treatment following dosage with 28 ml of herbicide solution (18.5% ai). Anatomically, plants grown in soils associated with herbicide-treated trees, both in the field and lab, grew less dry mass than non–herbicide treated controls. This study provides the first evidence that root exudation of herbicide following basal bark treatments contributes to non-target damage of adjacent vegetation and to accumulation of soil herbicide residues. This is an important new factor for integrated pest management within basal bark treatment systems and has implications for other herbicide application types such as injections and frill, as well as determining whether root exudation is species or herbicide specific.