Efficacy of imazapyr and its mixtures against weeds under rubber

Isopropylamine salt ofimazapyr is effective against several weeds in rubber plantations but is relatively more expensive. Lower rates ofimazapyr were therefore evaluated in mixtures with other herbicides to determine whether improved weed control can be obtained. Effectiveness of the herbicide using different nozzle types and spraying equipment were also evaluated. Trials were conducted along planting strips of rubber between one to six years’ old against weeds comprising mainly of Ottochloa nodosa, Paspalum conjugatum, Axonopus compressus, Borreria latifolia and Asystasia gangetica. Evaluation on efficacy of imazapyr showed weeds were susceptible at low rates of application, and acceptable control could be obtained at 0.2 kg ae/ha. Imazapyr at 0.375 kg ae/ha provided more effective weed control than standard treatments with pre-mixed paraquat +diuron (0.6 kg ai/ha 0.6 kg ai/ha), pre-mixed glyphosate +dicamba (0.54 kg ae/ha 0.27 kg ae/ha), glufosinate ammonium (0.5 kg ai/ha) and slashing. Lower rate of imazapyr at 0.15 kg ae/ha in mixture with ametryn (0.5 kg ai/ha or 1.0 kg ai/ha), metsulfuron methyl (0.015 kg ai/ha) or pre-mixed isopropylamine salt of glyphosate +isopropylamine salt of dicamba (0.18 +0.09,0.36 +0.18 or 0.54 0.27 kg ae/ha) improved weed control while its mixture with diuron (0.5 kg ai/ha or 1.0 kg ai/ha) provided comparable control. Addition of alachlor (0.48 kg ae/ha or 0.96 kg ae/ha), metolachlor (0.36 kg ae/ha or 0.72 kg ae/ha) or oxyfluorfen (0.12 kg ae/ha or 0.24 kg ae/ha) to imazapyr at 0.25 kg ae/ha provided comparable control to imazapyr alone. Comparison of fan, hollow cone and solid cone nozzles showed comparable weed control with imazapyr at 0.375 kg ae/ha. Application of imazapyr at 0.375 kg ae/ha with the controlled droplet applicator showed improved weed control compared to the knapsack sprayer.