The susceptibility of rice cultivars IRGA 417, BR-IRGA 410, BRS Pelota and Qualimax 1 was evaluated using a simulated drift of the herbicide imazethapyr + imazapic as a function of timing of flooding. The experiment was conducted under greenhouse conditions during the 2003/2004 growing season. The experimental design was arranged in randomized blocks with four replications. Treatments consisted of drift simulation by applying increasing herbicide doses at the following rates: 0%, 3.125%; 6.25%; 12.5%; 25%; 50% or 100% of the commercial dose (amended with Dash at 0.5% v/v), on rice plants at the V3 to V4 growth stages. Flooding was applied either three days prior or after treatment application. Herbicide was applied using a CO2 pressurized costal sprayer (flat fan nozzles 110.015 on the boom) at 150 L ha-1 with a constant pressure of 210 kPa. Phytotoxicity, expressed in percentage, was evaluated visually at 10, 15 and 20 days after treatment (DAT). Plant and root dry mass were evaluated at 25 DAT. Results showed that herbicide drift promoted toxic effects to rice plant under both dry and flooding conditions. Plant dry mass was significantly reduced with increasing herbicide dosage, regardless of timing of flooding. Cultivar IRGA 417 was the most sensitive to imazethapyr + imazapic simulated drift.
phytotoxicity; dry mass; imazethapyr + imazapic
