Creeping Bentgrass Phytotoxicity and Photochemical Efficiency Response to Amicarbazone.

Amicarbazone is a new herbicide currently being evaluated for potential control of annual bluegrass (Poa annua L.) in creeping bentgrass (Agrostis palustris Huds.).  Amicarbazone is a photosystem II inhibiting herbicide, similar in mode of action to atrazine and simazine.  Research was conducted to evaluate creeping bentgrass physiological response to increasing rates of amicarbazone compared to standard rates of paclobutrazol.  Amicarbazone rates were 0.1, 0.2, 0.3, and 0.4 kg ai/ha.  Paclobutrazol rates were 0.6 and 1.2 kg ai/ha.  All treatments were applied with 0.25% v/v non-ionic surfactant to a creeping bentgrass putting green.  Physiological response was measured utilizing a pulse-modulated chlorophyll fluorometer and photochemical efficiency (Fv/Fm) measurements were standardized relative to the non-treated.  All amicarbazone treatments decreased creeping bentgrass Fv/Fm greater than the non-treated and paclobutrazol treatments at 7 and 14 days after treatment (DAT).  Amicarbazone at 0.1 kg ai/ha decreased Fv/Fm 47% compared to the non-treated and measurements continued to decrease as rates were increased.  Amicarbazone at 0.3 kg ai/ha, decreased Fv/Fm 78, 53, 39, 20, and 12% compared to the non-treated at 7, 14, 21, 28, and 42 DAT respectively.  Paclobutrazol at 0.6 kg ai/ha decreased Fv/Fm 14% at 7 DAT while at 1.2 kg ai/ha Fv/Fm was similar to the non-treated.  All treatments recovered by 42 DAT.  The results of this study suggest that increasing rates of amicarbazone do reduce the photochemical response of creeping bentgrass compared to standard rates of paclobutrazol.