Postemergence Control of Annual Bluegrass with Mesotrione in Kentucky Bluegrass

Six field trials were conducted in 2009 and 2010 to study postemergence control of annual bluegrass (Poa annua L. var. Hausskn Timm) in kentucky bluegrass (Poa pratensis L.) with mesotrione. Mesotrione was applied at 11 different rate and application intervals to an area of kentucky bluegrass that was naturally infested with annual bluegrass. Mesotrione rates of 56 g.ha(-1) applied two or three times per week for a total of 10 applications or 84 g-ha(-1) applied two times per week for a total of seven applications provided consistent control of annual bluegrass but required significant application labor and resulted in minor kentucky bluegrass injury. Other treatments that required fewer applications, 110 g.ha(-1) applied twice per week for five applications or 186 g.ha(-1) per week for three applications, also achieved high levels of control under high air temperatures, but control levels can vary significantly as temperatures fluctuate and seasons change. Mesotrione can successfully control annual bluegrass in kentucky bluegrass when frequent applications at low rates are applied or when environmental conditions are conducive to control.