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The pyrimidine herbicide aminocyclopyrachlor was evaluated for crop tolerance and weed control in wild blueberry (Vaccinium angustifolium Aiton). Preemergence applications of aminocyclopyrachlor at a rate of 50 g a.i. ha−1 did not reduce aboveground blueberry biomass, yield potential, or final yield, and this rate appears safe for use in wild blueberry. Preemergence applications of aminocyclopyrachlor at a rate of 100 g a.i. ha−1 reduced aboveground blueberry biomass, but yield potential and final yield were only reduced significantly at application rates of 200 and 400 g a.i. ha−1. Preemergence applications of aminocyclopyrachlor at a rate of 100 g a.i. ha−1 effectively suppressed Euthamia graminifolia (L.) Nutt., and further evaluation of aminocyclopyrachlor to identify safe application timings and rates in wild blueberry is warranted. Aminocyclopyrachlor applied as a directed spot spray provided good control of several herbaceous and woody perennial weeds, and this use pattern could provide an alternative management option for many perennial weeds in wild blueberry.

Miller, A. J., Bork, E. W., Hall, L. M. and Summers, B. 2015. Long-term forage dynamics in pastures sprayed with residual broadleaf herbicide: A test of legume recovery. Can. J. Plant Sci. 95: 43–53. Legumes such as alfalfa (Medicago sativa L.) and white clover (Trifolium repens L.) are important components of northern temperate pastures where they increase forage productivity and quality, but are susceptible to decline when exposed to broadleaf herbicides. Little is known about the long-term sward responses following herbicide use in northern temperate pastures, including the recovery of legumes and their subsequent contribution to forage production. We established five field sites over 2 yr to assess changes in grass, legume, total forage (grass+legume) and other forb biomass, as well as the recovery of a common weed, dandelion (Taraxacum officinale Weber), for up to 3 yr following a single application of two broad leaf herbicides with residual properties (aminopyralid and aminocyclopyrachlor). The importance of defoliation and the legume seed bank in facilitating legume biomass recovery were also evaluated with mowing and legume overseeding, respectively, in a strip/split-split design. Both herbicides had similar functional impacts on sward composition based on peak annual biomass, reducing legume biomass by an average of 71–100% across the 3 yr, equivalent to 63.4–22.6 g m−2 from year 1 to year 3, respectively. Although grass biomass did not change significantly with herbicides, net reductions in total forage were limited to 6.8% (28 g m−2) over the study, suggesting at least some ability of grasses to compensate for legume removal. Legume biomass was greater following overseeding and only in non-sprayed controls, but then decreased over time. Conversely, biomass of other forbs and cover of dandelion were lower shortly following herbicide application, only to reach levels similar to non-sprayed controls by the second growing season. Defoliation also influenced sward composition, favoring dandelion recovery following herbicide application. As both weed control and legume re-establishment are important objectives for livestock producers, the result of this study provides useful insight into the long-term impact of broad-leaf weed control on forage production in mixed swards of northern temperate pastures.