Spotgun-Applied Hexazinone: Release of Red Pine (Pinus resinosa) from Quaking Aspen (Populus tremuloides) Competition and Residue Persistence in Soil

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Abstract
Weed control and red pine release by spotgun-applied hexazinone in a northern Ontario plantation were evaluated 3 yr after treatment, while hexazinone residues and lateral movement in the sandy loam soil were determined 1 yr after treatment. Hexazinone, grid pattern spot applied at 480 mg ai/spot, approximating 1.6 kg ai/ha, resulted in 88% quaking aspen stem dieback and variable suppression of white birch and pin cherry. The height and basal diam of treated red pine were 131 and 150% of control, respectively, after 3 yr. Hexazinone residues were reduced to 1% at the treated spot and did not move laterally beyond 0.5 m, 1 yr after treatment. Detection of small amounts of metabolites A and B (0.2 and 0.3%) indicated the non-cumulative degradation of hexazinone in soils.