Phytotoxicity of imazapyr+imazapic on tolerant rice varieties Guri INTA CL and IRGA 424 RI

ABSTRACT Rice varieties from the Clearfield® system may present different tolerance levels to imidazolinone herbicides in function of application rate. The objective of this research was to evaluate the phytotoxicity of different rates of the formulated mixture of the herbicides imazapyr+imazapic applied on two tolerant irrigated rice varieties. The experiment was carried out in 2015/16 and 2016/17 growing seasons. A randomized complete block design was used in a factorial 2x6 with five replications. The factor A was composed by the tolerant rice varieties Guri INTA CL and IRGA 424 RI, and the factor B by rates of the formulated mixture of the herbicides imazapyr+imazapic (525+175 g a.i. kg-1) of 0, 140, 210, 280, 350, and 420 g c.p. ha-1. In the first growing season, it was observed maximum phytotoxicity of 8.5% while in the second the highest percentage was 13%. The number of stems m-2, plant height, shoot dry matter, SPAD index, and grain yield were not influenced (p≥0.05) by herbicide rates. The application of the formulated mixture of the herbicides imazapyr+imazapic causes low initial phytotoxicity to the tolerant rice varieties Guri INTA CL and IRGA 424 RI up to three times the recommended rate, not influencing their grain yield.