WINTER-WHEAT (TRITICUM-AESTIVUM) GROWTH STAGE EFFECT ON PARAQUAT BIOACTIVITY

Paraquat was applied at 0.28 and 0.56 kg ai ha-1 to winter wheat at five growth stages at 0800, 1300, and 1600 hr to determine whether growth stage or time of application influenced winter wheat response to paraquat. Paraquat bioactivity was affected by growth stage. Biomass reduction by paraquat was 84% when winter wheat was in the 1 to 3 leaf stage, but only 68% when application was delayed until tillering. Paraquat bioactivity continued to decrease at later growth stages. The time of day when paraquat was applied did not affect its bioactivity on winter wheat.