Short-term performance of two hexazinone formulations: efficacy, seedling survival and growth

Liquid (VELPAR L) and dry-flowable (VELPAR ULW) hexazinone (2 kg ai ha-1) were aerially applied to a northern New Brunswick clearcut to reduce raspberry [Rubus idaeus L. var. strigosus (Michx.) Maxim] competition. Treatments were applied in June 1987; planting with containerized (multipot) black spruce [Picea mariana (Mill.) B.S.P.] was conducted 2 and 14 months after treatment in August 1987 and 1988. Seedling survival and growth were measured yearly through August 1991. Hexazinone formulation did not affect raspberry control seedling survival, or growth. Five growing seasons after treatment, raspberry cover was generally less in treated plots than in controls. Seedling survival did not differ among treatments for seedlings planted at either time interval after hexazinone treatment. Seedlings planted 14 months after hexazinone treatment grew poorly compared with those planted 2 months after herbicide treatment. Stem volume of seedlings planted 2 months after hexazinone treatment exceeded that of control seedlings in the first growing season after planting and remained greater than that of control seedlings through 1991. Stem volume increases over controls were restricted to the second growing season after planting for seedlings planted 14 months after hexazinone treatment. Fourth-year stem volume of seedlings planted 2 months after hexazinone treatment was correlated with raspberry cover (r2 = 0.34) As raspberry cover increased, black spruce growth decreased.