Hexazinone site preparation improves black spruce seedling survival and growth

Granular (PRONONE 10G and 5G) and liquid (VELPAR L) hexazinone (1 to 4 kg ai ha −1 ) were applied to a northern New Brunswick clearcut (loams, silt loams, and clay loams) to reduce raspberry [Rubus idaeus L. var. strigosus (Michx.) Maxim] competition. Treatment, using skidder-mounted herbicide application equipment, was completed in May and September 1986, with planting of 2+2, bareroot, black spruce seedlings [Picea mariana (Mill.) B.S.P.] in June 1986 and in June 1987. Seedling survival and growth were measured yearly for five growing seasons after planting. By August 1991, raspberry cover for three treatments remained less than that for controls. Survival of seedlings planted approximately one month after spring treatment was less than controls, but seedling height and stem diameter were greater than that of control seedlings for most treatments. Survival and growth of seedlings planted approximately one year after spring treatment or nine months after fall treatment were greater than that of control seedlings for most treatments. Fifth-year height and stem diameter of seedlings planted nine months after fall treatment were negatively correlated with raspberry height (r 2  = 0.729, height and 0.745, diameter), decreasing as raspberry height increased. Over the five-year observation period, hexazinone formulation did not affect raspberry control, but did affect seedling survival and growth. Spring treatment with PRONONE 10G (2 kg ai ha −1 ), with planting delayed by one year, provided the best treatment to achieve both optimal seedling survival and growth during plantation establishment. Key words: liquid hexazinone, granular hexazinone, site preparation, black spruce, growth parameters, seedling survival, raspberry competition