Effect of stage of phalaris minor on the efficacy of accord plus (fenoxaprop+ metsulfuron, readymix)

Screen house and field studies were carried out at CCS Haryana Agricultural University, Hisar during 2009_10 and 2010_11 to evaluate the efficacy of ready-mix formulation of fenoxaprop and metribuzin (Accord Plus) applied at two growth stages of Phalaris minor. Metribuzin 150, 180 and 210 g/ha and Accord Plus 275 g a.i./ha were compared with tank mix of pinoxaden+carfentrazone 50+20 g/ha each applied at 38 and 60 days after sowing (DAS) of wheat under field conditions during 2010_11. Delayed application resulted in 33 and 28% reduced efficiency of herbicides against P. minor, respectively, at 3 and 5 weeks after treatment (WAT) (data averaged over treatments). Metribuzin 150 and 180 g/ha was least effective against P. minor when applied 60 DAS, whereas its application at 210 g/ha and Accord Plus resulted in 44 and 16% lower mortality of P. minor, respectively, over their application 38 DAS. Delayed application also lowered wheat tillers resulting in lower grain yield. Wheat yield was reduced by 23 and 18% by metribuzin 210 g/ha and Accord Plus 275 g a.i./ha compared to 14% in tank mix of pinoxaden+carfentrazone when applied 60 over 38 DAS. Under screen house conditions, 19 populations of P. minor were evaluated at two growth stages (2_4 leaf and 4_6 leaf) with three rates of Accord Plus (137.5, 275 and 550 g a.i./ha) during 2009_10 and 2010_11. Mortality of P. minor populations was 44, 65 and 97% at the 4_6 leaf stage of application compared to 83, 98.5 and 100% when applied at the 2_4 leaf stage, respectively, with three rates of Accord Plus (data averaged over populations). Accord Plus 275 g a.i./ha applied at the 2_4 leaf stage provided 90_100% control of all the populations of P. minor, whereas delayed application at 4_6 leaf stage provided 45 to 85% control. P. minor populations, Rasidan, Nangla, Barhi, Suchan Kotli and Uchana were controlled by 50% by 275 g a.i./ha of Accord Plus application at 4_6 leaf stage. P. minor populations, Barhi, Suchan Kotli, Koyal, Jakholi and Chanarthal were not completely knocked down by even 550 g a.i./ha of Accord Plus with delayed application at the 4_6 leaf stage. Some of these populations have already exhibited loss of efficacy against fenoxaprop and clodinafop under field conditions. Care need to be taken in timely application of Accord Plus where efficacy of one of the mixture partners (fenoxaprop) is questionable.