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Abstract
Efficacy of Imazapyr and Its Mixtures against Weeds Under
Rubber
Isopropylamine salt of imazapyr is effective against
several weeds in rubber plantations but is relatively more expensive. Lower
rates of imazapyr 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.

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