Abstract
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.
Highlights
Facing the need of alternatives to control weedy rice (Oryza sativa), tolerant rice varieties to imidazolinone herbicides of the Clearfield® system were developed. Herbicides belonging to this chemical group act on the inhibition of the acetolactate synthase enzyme (ALS), which acts on the synthesis of the branched chain amino acids valine, leucine, and isoleucine (Sudianto et al, 2013)
Despite its considerable expressiveness on the rice productive chain in that state, the knowledge about the tolerance level of IRGA 424 RI to imidazolinone herbicides is limited due to its shorter usage time in relation to Guri INTA CL, which has been in the market for the longest time
At 7 DAA it was observed a maximum value of 7.5% in the highest applied rate, while at 14 DAA there was an increase of 1% for that same rate in relation to the previous evaluation
Summary
Facing the need of alternatives to control weedy rice (Oryza sativa), tolerant rice varieties to imidazolinone herbicides of the Clearfield® system were developed. The responses to different herbicides of the imidazolinones chemical group, as well as to different rates, are dependent of the variety tolerance level, which Phytotoxicity of imazapyr+imazapic on tolerant rice varieties Guri INTA CL and IRGA 424 RI
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