The economic merit of controlling brush regrowth using combinations of 2,4-D and dicamba with different patterns of repeat applications was assessed for pastures in east-central Saskatchewan. Two experiments were conducted simultaneously in a community pasture located on a Waitville loam. The area, which was originally dominated by aspen poplar (Populus tremuloides Michx.), had been cleared of trees and shrubs by bulldozing before the start of the tests. In the first experiment started in 1981, 2,4-D ester plus dicamba and 2,4-D amine plus dicamba were foliar applied to the brush regrowth. Single applications were compared with repeat sprayings in the first, second, or in both years following the initial herbicide application. A subset of these treatments was used in a second experiment started in 1983 to determine whether or not productivity effects were influenced by growing conditions in the initial year of spraying. Herbicides effectively controlled brush regrowth which increased yields of useable herbage (grasses plus forbs) by an average of 32–39%. The forage benefits did not decline with time to the end of the study in 1989. Herbicide treatments were generally more profitable when applied to younger stands of brush regrowth, with the 2,4-D ester formulations being more profitable than 2,4-D amine formulations. Economic returns were highest, although not always positive, for the treatment receiving a one-time application of 2-4-D ester at 2.2 kg ha−1 plus dicamba at 1.5 kg ha−1 for forage values between $25 and $75 t−1 (dry weight) and discount rates between 0 and 10%. In order to justify this treatment cost, the minimum value that must be obtained when utilizing the additional forage was $20 t−1 (dry weight) for the most profitable control treatment, assuming a 5% discount rate and persistance of the treatment effects for up to 18 yr. For the other treatments, breakeven forage values ranged between $37 and 70 t−1 under similar assumptions. Higher discount rates or a shorter effective treatment life increased breakeven forage values. Repeat herbicide applications could not be justified under any of the economic scenarios. Key words: Net present value, benefit-cost ratios, discount rate, aspen poplar, herbicides, 2,4-D
Selection of a discount rate for use in NRC regulatory analyses and application of discount rates to future averted health effects
