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

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 field and laboratory experiments were quantified with analytical detection and plant bioassay. Aminopyralid soil residues were identified in 57% of field treatments receiving 8-60 ml herbicide solution (2% ai) and 70% of laboratory treatments receiving 10 µl herbicide solution (2-16% ai). Triclopyr residues were found from one field treatment following dosage with 28 ml herbicide solution (18.5% ai). Anatomically, plants grown in soils associated with herbicide-treated trees, 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 if root exudation is species or herbicide specific.

Physical and physiological pathways of off-target triclopyr movement and associated non-target injury following basal bark application

“…Although we only tested the triclopyr acid formulation, results are in agreement with previous investigations of root exudation of the butoxyethyl ester formulation. These concluded it is limited and unlikely to result in non-target injury (Eck and McGill 2007; Graziano et al 2022; Harrington et al 2016; Kochenderfer 1999). Additionally, although not part of this study, the transfer of herbicides from target plants to non-target vegetation through interspecific root grafting is also rare and has not been observed with triclopyr (Eck and McGill 2007; Futch and Weingarten 2010; Kochenderfer et al 2006; Willoughby 1999).…”

“…We recommend the use of triclopyr for basal bark treatments when non-target injury must be avoided. However, land managers should anticipate greater triclopyr release and an elevated risk for non-target injury when performing basal bark treatments in high-density plant infestations, due to increased herbicide output (Graziano et al 2022). We recommend that future research should focus on investigating alternative mechanisms of non-target injury that remain untested for triclopyr, as well as approaches that seek to improve triclopyr herbicide stewardship in basal bark treatments.…”

“…Precipitation and flooding events can lead to herbicide wash-off from treated stems and foliage, contributing to runoff, off-target herbicide deposition, and the accumulation of herbicide residues in soil (Harrington et al 2016;Holmes and Berry 2009;Norris et al 1987;Nowak and Ballard 2005;Wilcock et al 1991). This can increase non-target plant exposure to herbicide (Graziano et al 2022;Holmes and Berry 2009). Nowak and Ballard (2005) reported a 0.5-m radius of non-target injury during basal bark treatments of triclopyr ester.…”

Herbicide Uptake (Flashback) in Non-target Hardwood Species Within South Carolina Floodplains

“…Likewise, triclopyr amine salt (found in Garlon 3A) has persisted in soil up to a year after treatment on silt clay loam soils [27]. Graziano et al [5] found a limited amount of non-target chokecherry damage associated with triclopyr treatments (only 5% of treatments) found in soil residue, where as, aminopyralid (residual soil active herbicide) was found in 57% of field treatments. The study also stated that non-treatment soils had greater plant dry mass compared to soils with herbicide treated trees.…”

“…Eck [3] did not observe any damage (wilting, axillary budding, chlorosis, and necrosis) to adjacent stems within treatments using triclopyr as basal bark applications (Garlon 4 ® ) or stem injection using triclopyr (amine formulation) capsules. Limited flashback damage (5% of treatments) of triclopyr ester (Garlon 4®) into non-target stems was observed by Graziano et al [5]. Turner et al [6] found that a combination of triclopyr amine (50%), water (40%), and imazapyr (10%) gave better control of more species compared to triclopyr (amine) alone in older stands.…”