Short-Term Performance of Three Hexazinone Formulations: Efficacy, Seedling Survival, and Growth

Granular (PRONONE 10G and 5G) and liquid (VELPAR L) hexazinone (1 to 4 kg ai/ha) were applied to a northern New Brunswick clearcut (loams, silt loams, and clay loams) to reduce raspberry competition. Treatment, using skidder-mounted herbicide application equipment, occurred in May and September 1986, with planting of 2+2, bareroot, black spruce seedlings in June 1986 and in June 1987. Seedling survival and growth were measured yearly for 5 growing seasons after planting. By August 1991, hexazinone formulation did not affect raspberry control, seedling survival, or growth. Raspberry cover for the 4 kg ai/ha treatment and for fall treatments remained less than that for controls. Survival of seedlings planted approximately 1 month after spring treatment was less than controls, but seedling stem volume was greater than that of control seedlings for most treatments. Survival and stem volume of seedlings planted approximately 1 yr after spring treatment or 9 months after fall treatment were greater than that of control seedlings for most treatments. Best survival and growth occurred for seedlings planted 1 yr after spring treatment. Fifth-year stem volume for these seedlings was correlated with raspberry cover (r2 = 0.35), decreasing as raspberry cover increased. We conclude that the use of the PRONONE 10G formulation offers operational advantages over the liquid formulation. North. J. Appl. For. 13(1):41-45.