Abstract
ABSTRACT: The use of imidazolinone-tolerant rice cultivars allows selective control of weedy rice and barnyardgrass. However, in many situations, there is a need to add herbicides from other chemical groups to increase the spectrum of weed control. In this sense, saflufenacil has the potential to be used in mixture with imidazolinone herbicides. This study aimed to evaluate the interaction effects of the imazapyr+imazapic and saflufenacil herbicides in weedy rice and barnyardgrass and to investigate their impacts on the yield of the irrigated rice cultivar Puitá INTA CL. To reach these aims, greenhouse and field experiments were carried out during two growing seasons, with herbicide treatments sprayed separately and in mixtures of saflufenacil with imazapyr+imazapic. Results showed that saflufenacil did not interfere with control of weedy rice and barnyardgrass obtained with imazapyr+imazapic. The D50 values of imazapyr+imazapic for weedy rice control were 14.5+5, 9.1+3 and 12.5+4.2 g ha-1of imazapyr+imazapic for combinations with 0, 3.06 and 6.12 g ha-1of saflufenacil, respectively. In the field experiments, all doses of imazapyr+imazapic applied isolated or in mixture with saflufenacil provided control levels barnyardgrass above 90% at 28 days after herbicides application. Furthermore, saflufenacil did not cause damage or loss in the yield of the rice crop when mixed with imazapyr+imazapic. The Puitá INTA CL rice cultivar was tolerant of the tested herbicides, whether applied alone or in mixture, reaching grain yield of 9.987 kg ha-1 when applied 42 g ha-1 of saflufenacil plus 147+49 g ha-1 of imazapyr+imazapic.
Highlights
The Clearfield® system has become an indispensable tool for selective control of Poaceae weed species, as weedy rice and barnyardgrass
The intensive adoption and misuse of this technology has led to the selection of resistant weeds, the weedy rice (Oryza sativa) and the barnyardgrass (Echinochloa crus-galli) and giant arrowhead (Sagittaria montevidensis); and this has led the use of other herbicides to control these species (MENEZES et al, 2013; MOURA et al, 2016; NUNES et al, 2016; HEAP, 2018)
Some changes have been established to aid in the chemical management, among them, the herbicide mixture, which aims to increase action spectrum and efficiency of weed control, such as red rice (Oryza sativa), Echinochloa crus-galli, Sesbania exaltata, Ipomoea hederacea, Alternanthera philoxeroides (PELLERIN et al, 2003; PELLERIN et al, 2004; CARLSON et al, 2011; MONTGOMERY et al, 2015; FISH et al, 2016)
Summary
The Clearfield® system has become an indispensable tool for selective control of Poaceae weed species, as weedy rice and barnyardgrass In this system, imidazolinone-resistant cultivars are grown with the application of imidazolinone herbicides in pre and/or post-emergence (IRGA, 2018; SOSBAI, 2018). The intensive adoption and misuse of this technology has led to the selection of resistant weeds, the weedy rice (Oryza sativa) and the barnyardgrass (Echinochloa crus-galli) and giant arrowhead (Sagittaria montevidensis); and this has led the use of other herbicides to control these species (MENEZES et al, 2013; MOURA et al, 2016; NUNES et al, 2016; HEAP, 2018). The herbicides mixtures can result in three different types of interactions, which can be an additive, synergistic or antagonistic interaction. The interaction of herbicides mixture can produce opposite effects on the same physiological process of the plant or synergizes the overall effect (COLBY, 1967; DAMALAS, 2004; KUDSK & MATHIASSEN, 2004)
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