Response of desirable trees to aminocyclopyrachlor in the field and greenhouse
Date
2017
Authors
Hildebrandt, Curtis M., author
Westra, Philip, advisor
Borch, Thomas, committee member
Jacobi, William R., committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Aminocyclopyrachlor is a selective, plant growth regulator herbicide in the pyrimidine carboxylic acid family. Previously, aminocyclopyrachlor was marketed for turfgrass management but was withdrawn by the EPA in light of unexpected non-target injury related to desirable tree species such as white pine (Pinus strobus), and Norway spruce (Picea abies). Field trials to assess the impact of aminocyclopyrachlor on two tree species green ash (Fraxinus pennsylvanica) and honeylocust (Gleditsia triacanthos) were conducted to determine the relative sensitivity of green ash and honeylocust to aminocyclopyrachlor, determine a minimum safe spraying distance from green ash and honeylocust trees, and to assess the effect of application timing on tree response. An additional greenhouse dose response trial on tree seedlings was used to compare green ash and honeylocust response to Norway spruce which had demonstrated high sensitivity to aminocyclopyrachlor, and blue spruce which is a common and important native species in Colorado. Field results showed that green ash was not susceptible to herbicide applications while honeylocust showed severe injury, up to 100% for trees closest to applications. Honeylocust trees up to 7 m from the edge of the application displayed moderate to severe injury symptoms, and the fall treatment timings in October and November appeared to be safer in terms of reducing injury on target trees. Soil analysis using LC-MS and HPLC demonstrated that aminocyclopyrachlor dissipation was no different in the soil underneath green ash and honeylocust trees, and that dissipation was likely aided by absorption in tree roots. A greenhouse dose response showed that honeylocust was a moderately sensitive species, about four times more tolerant to aminocyclopyrachlor than blue spruce or Norway spruce. Green ash was consistently tolerant to aminocyclopyrachlor in the greenhouse, showing only minor response at the higher doses. Taken together these results provide a basic groundwork of research necessary for the writing of better aminocyclopyrachlor herbicide labels, and a better understanding of this herbicide's effect on certain woody vegetation.