LENGTH OF RESIDUAL ANNUAL BLUEGRASS CONTROL OF MESOTRIONE RELATIVE TO OTHER PREEMERGENCE WEED CONTROL PRODUCTS. S. Hart, C.J. Mansue, and K.A. Venner*, Rutgers University, New Brunswick, NJ (13)
Field studies were conducted in the fall of 2009 and 2010 to evaluate the length of residual weed control of annual bluegrass (Poa annua) on bare soil. Herbicides were applied to bare soil (Freehold sandy-loam with pH 6.4 and 2% organic matter). The compounds under evaluation were: mesotrione at 0.28 and 0.43 kg ai/ha, dithiopyr at 0.28 and 0.43 kg ai/ha, prodiamine at 0.57 and 0.74 kg ai/ha, and bensulide at 9.41 and 11.91 kg ai/ha. All applications were made using a single 9504EVS nozzle CO2 pressured sprayer calibrated to deliver 378 L/ha at 207 kPa. The study was visually evaluated at 4 and 8 weeks after treatment (WAT) and the following spring for Poa annua control. The plots were evaluated for percent control and percent cover of Poa annua, both on a scale of 0 (no control or cover) to 100 (complete control or cover). Annual broadleaf weeds were evaluated also at 4 WAT. Control of Poa annua ranged from 70% to 90% between the four compounds examined. Mesotrione was the only compound which showed significant difference between rates applied, 70% and 86%, respectively. All other compounds provided between 79% and 90% control, respectively. In springtime, mesotrione was found to only provide 31% to 44% control of Poa annua as opposed to the 81% to 85% provided by dithiopyr, 81% to 89% provided by prodiamine and 82% to 85% provided by bensulide. Annual broadleaf weeds, common chickweed (Stellaria media) and henbit (Lamium amplexicaule), were controlled with mesotrione. The result of one year of research suggests that the broad spectrum herbicides (dithiopyr, prodiamine, and bensulide) control Poa annua better than mesotrione as demonstrated by decreased control of mesotrione over time.