Department of Agronomy, CCS Haryana Agricultural University, Hisar-125 004 (Haryana), India.
Isoproturon resistant biotypes of Phalaris minor have spread to over 1 m ha of N-W India causing a threat to the option of chemical weed control in wheat. The resistant biotypes have been found to degrade isoproturon by enhanced detoxification mediated by cyto P450 monooxygenase enzymes. Herbicides of different modes of action are required to combat the evolution of cross-resistance in weed species. Experiments were conducted to evaluate the efficacy of JV-485 (isopropazol) and Mon-37500 (sulfosulfuron) against the resistant (R) and susceptible (S) biotypes of P. minor and selectivity against wheat. Plants of R and S biotypes and wheat were raised in a glasshouse and isopropazol was applied pre-emergence; isoproturon and sulfosulfuron (±0.2% surfactant) were applied postemergence 21 days after sowing (DAS) at the 2–3 leaf stage of P. minor and 3–5 of wheat and 35 DAS at 4–6 leaf stage of P. minor with four replicate pots for each treatment. Plants were sprayed using a motorized track sprayer fitted with a flat fan even spray nozzle at 300 kPA pressure delivering 200 I water/ha. Observations were periodically recorded for visual mortality and fresh/dry weights were recorded 4–6 weeks after treatment (WAT). Wheat was relatively safe to the treatments of isopropazol upto 100 g/ha which was >16 times the GR50 values for the P. minor biotypes. Mon-37500 was equally safe to wheat and there was no growth inhibition at 20 g/ha (+surfactant). Both these herbicides were highly effective against isoproturon resistant biotypes of P. minor. Mon-37500 was effective even upto 4–6 leaf stage of P. minor, some variations though were observed among the biotypes. Surfactant (0.2% Mon-0818) enhanced the efficacy of Mon-37500 and is desired to use under field conditions.
