Publicação on-line; 28 ref.; 7 tables; Summary (En)

ABSTRACT
Background: Weed management is a challenge in paddy rice production,
mainly due to the dispersal of a population resistant to herbicides.
Objective: To assess the efficacy of chemical weed control in the offseason to
reduce weedy rice and other species in water-seeded or drilled
rice.
Methods: Two experiments were carried out in a flat field to water-seeded
or drilled rice, in randomized block design. The water-seeded system
treatments were organized in a split-plot design. In the plot were evaluated
two water management in the off-season (with or without continuous
flooding), and in the subplot nine herbicides-treatments were evaluated
(Check, clomazone at 0.72 and 1.08 kg a.i. ha-1, oxadiazon at 1.00 and
1.50 kg a.i. ha-1, oxyfluorfen at 0.312 and 0.48 kg a.i. ha-1, S-metolachlor at
1.44 kg a.i. ha-1, and flumioxazin a 0.075 kg a.i. ha-1). In the drilled rice
experiment, the treatments were organized in a two-factor factorial. The
factor A was nine herbicides treatments (the same herbicide and rates
applied in water-seeded experiment) and the factor B was two application
time (73 and 43 days before of rice-sowing).
Results: Off-season management was efficient to reduce weedy rice
infestation only on the paddy rice system using the pre-germinated seeds.
In this assay, flumioxazin was an efficient alternative to giant arrowhead
control, however the selectivity of this herbicide treatment needs to be
studied. In dry-seeded system, herbicide sprayed in off-season reduced
barnyardgrass infestation until the paddy rice sowing.
Conclusions: The off-season management was efficient to reduce weedy
rice and giant arrowhead infestation in water-seeded system, and
barnyardgrass infestation in drill-seeded system.

Keywords:
drill-seeded
water-seeded
residual herbicides
pre-germinated
Oryza sativa