The objective of this study was to evaluate the residual soil activity of herbicide (imazethapyr+imazapic), labeled for the Clearfield (CL) system and using corn, cv. Biomatrix 2202, as a bioindicator. The study was carried out in a greenhouse, at the Universidade Federal de Pelotas, in southern Brazil. Rice, cv. IRGA 422 CL, was planted in boxes (60 x 40 x 20 cm). At the 3-4 leaf stage, the herbicide Only (imazethapyr+imazapic) was sprayed at 0; 25+75; 37.5+112.5 and 50+150 g ha-1. After harvesting the rice, boxes were kept without flooding for 45 days. Black oat (Avena strigosa) was planted to keep the soil covered during the winter. In the spring, oat was harvested and 360 or 540 days after herbicide aplication (DAA), the soil from the boxes was transferred to two sets of pots labeled as experiment 1 (main corn crop) and experiment 2 (minor corn crop), respectively. The soil for experiment 2 was kept drained during the time period between seeding the two studies (360 to 540 DAA). Corn was planted in both studies and harvested at the 4-5 leaf stages. The variables evaluated were shoot and root biomass, plant height and leaf area index (for experiment 2). The data from both studies were analyzed using ANOVA (<0.05), and tested as polynomial models, when significant. A significant reduction was observed in shoot and root biomass, plant height and leaf area index planted up to 540 days after (imazethapyr+imazapic) aplication to CL rice. Corn cv. Biomatrix 2202 showed to be a good bioindicator of soil residual activity for the herbicide (imazethapyr+imazapic) in the CL system.
red rice; Clearfield® rice; imidazolinones; soil persistence
