Herbicide Release of 3-Year-Old Loblolly Pine from Competing Hardwoods in Arkansas
Abstract Objectives were to identify effective late-summer and spring herbicide treatments for the release of 3-yr-old loblolly pine (Pinus taeda L.) from competing hardwoods and to quantify longer term pine growth response to varying levels of hardwood control. Effective late-summer treatments included imazapyr at 1.0 and 0.5 lb ae/ac, imazapyr at 0.5 lb ae/ac in combination with glyphosate at 1.125 lb ae/ac, and imazapyr at 0.25 lb ae/ac with surfactant. The best spring treatment was hexazinone at 2.0 lb ai/ac. Although spring imazapyr treatments stunted pine height growth 2 growing seasons after treatment, height growth had recovered by age 10. Late-summer imazapyr treatments provided better hardwood control than spring treatments. Although check plot hardwood basal area averaged 9 ft2/ac, and winged elm (a species known to be tolerant to imazapyr) was the predominant hardwood species at treatment, pine basal area response to treatment ranged from 6 to 27 ft2/ac at age 10. Pine response increased with imazapyr rate for late-summer treatments. Adding hexazinone to imazapyr did not improve hardwood control, and no benefits were observed from adding metsulfuron to either glyphosate or hexazinone. South. J. Appl. For. 20(3): 121-126.