Assessing legume tolerance to residual broadleaf herbicides in northern temperate pastures using short-term dose trials.
Amanda Miller
Edward Bork
Linda Hall
Patrick Forsythe
Bill 0
Publication Year

Legumes such as alfalfa (Medicago sativa) and white clover (Trifolium repens) are beneficial features of northern temperate pastures due to their role in increasing forage productivity and quality. Little is known about the tolerance of legumes to broadleaf herbicides in northern soils and climates, including legume ability to regenerate from the seed bank once removed. We used a variable rate herbicide field study to assess 1) tolerance of existing legumes to herbicide bioactives, and 2) seedling performance of key forage legumes (alfalfa and white clover) from an augmented soil seed bank. This study was conducted at two sites over two years using broadleaf herbicide bioactives (aminopyralid and aminocyclopyrachlor), each applied at 6 different rates (0x, 0.0625x, 0.125x, 0.25x, 0.5x, and 1x) in a randomized block design with 4 replications. Sites were overseeded with 16 kg/ha of alfalfa and clover seed to populate seed-bank prior to herbicide application, and monitored for seedling emergence, survival and density over the following 12 months. Plots were further divided into mown and un-mown subplots to assess the role of forage competition on legume establishment. Legume performance differed modestly between the two different bioactives, with marked changes across the variable spray rates. Tolerance to herbicide and initial seedling establishment were also greater under mowing, likely due to decreased competition for light, moisture, and nutrients. Re-establishment of legumes is an important goal of producers, and this information provides insight into the expected return of legume populations in northern temperate pastures following spraying.

Additional Information
Amanda Miller1, Edward Bork1, Linda Hall1, Patrick Forsythe2, Bill 0 --- 1University of Alberta, Edmonton, Alberta, Canada, 2DuPont, Wetaskawin, Alberta, Canada