Efficacy of Several Herbicides on Yellow Archangel (Lamiastrum galeobdolon)

Yellow archangel is a twining perennial species that produces a dense evergreen canopy and may negatively affect forest floor vegetation. Because it is spreading rapidly in the Pacific Northwest (PNW), greenhouse and field trials were conducted on yellow archangel to determine its relative sensitivity to several herbicides. Products that slowed or prevented yellow archangel regrowth at 9 mo after treatment (MAT) in one or both iterations of the greenhouse trial were aminopyralid, diclobenil, glufosinate, imazapyr, isoxaben, metsulfuron, sulfometuron, triclopyr amine, and triclopyr ester + 2,4-D ester. In the field trial at 10 MAT, triclopyr and imazapyr were controlling 81 and 78% of treated yellow archangel, respectively, similar to aminopyralid, glyphosate, and metsulfuron (61 to 65%). Two applications of 20% acetic acid or 20% clove oil were controlling 53% at the same timing. At 13 MAT, only imazapyr and glyphosate were still providing good control of yellow archangel (81 and 80%, respectively), while all other products were controlling the weed at 53% or less. By 7 or 8 MAT after a second application, only imazapyr and glyphosate provided effective control of yellow archangel (86 to 94%).Nomenclature: 2,4-D, acetic acid, aminopyralid, clove oil, diclobenil, glufosinate, glyphosate, imazapyr, isoxaben, metsulfuron, sulfometuron, triclopyr, yellow archangel, Lamiastrum galeobdolon (L.) Ehrend. & Polatschek.Management Implications: Yellow archangel is a fast-growing and dense-canopied perennial species that is quickly becoming problematic along both coasts of the United States and Canada, and is particularly troublesome in forest, park, and ornamental settings in western Oregon, Washington, and British Columbia. Because the susceptibility of yellow archangel to herbicides is not known, greenhouse and field trials were conducted to determine which products could be useful for land managers to aid in its control. Herbicides identified in greenhouse trials that rapidly defoliated yellow archangel included diclobenil, glufosinate, isoxaben, metribuzin, triclopyr amine, and triclopyr ester + 2,4-D ester. Those products, in addition to aminopyralid, imazapyr, isoxaben, metsulfuron, and sulfometuron, effectively reduced yellow archangel regrowth at 9 mo after treatment (MAT) in one or both iterations of that trial. In the field, triclopyr amine, 20% acetic acid, and 20% clove oil quickly defoliated yellow archangel. However, control with acetic acid or clove oil had declined to only 53% at 10 MAT even after two applications. Control at 10 MAT with triclopyr and imazapyr was 81 and 78%, respectively, statistically similar to aminopyralid, glyphosate, and metsulfuron (61 to 65%). By 13 MAT, only imazapyr and glyphosate were still providing good control of yellow archangel (81 and 80%, respectively) and by 8 mo after a second application, control with these herbicides was 93 and 86%, respectively. Because yellow archangel seedlings were found in several of the treated plots, it is important to consider the seedbank when control programs for well-established patches are planned and conducted, and when maintaining the site following initial treatment.