Carryover Effect of Imidazolinone Herbicides for Crops Following Rice

Abstract

We aimed with this study to evaluate the effects of residual activity in soil of formulated mixtures of the herbicides imazethapyr + imazapic and imazapyr + imazapic on ryegrass and on rice cultivars, IRGA 424 and BRS Querencia. Two experiments were conducted under greenhouse in randomized blocks design with four replications in split-plot and split-split-plot designs, respectively for the first (E1) and second (E2) experiments. For E1, main plots allocated herbicides (imazethapyr + imazapic and imazapyr + imazapic), and subplots the doses [(0, 0.5, 1.0, 1.5 and 2.0 fold the label dose of imazethapyr + imazapic (1 L·ha-1) and imazapyr + imazapic (140 g·ha-1) plus 0.5% of the adjuvant Dash→)]; for E2, sub-subplots allocated rice cultivars (BRS 424 and IRGA Querência). Phytotoxicity, plant height and shoot dry weight (E1 and E2) and plant stand (E2) were evaluated. Results showed that the annual ryegrass and rice cultivars IRGA 424 and BRS Querencia are sensitive to imazethapyr + imazapic and imazapyr + imazapic, serving as bioindicators of its residual activity in soils following Clearfield→ rice. Imazapyr + imazapic, applied post-emergence in irrigated rice at doses of 1.0, 1.5 and 2.0× the label dose, present longer residual activity in soil compared to imazethapyr + imazapic for ryegrass and non-Clearfield→ rice.