Abstract
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 off-season 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.
Highlights
In Santa Catarina, paddy rice culture is carried out in two production systems, covering approximately 80% and 20% of the cultivated area, respectively (Sosbai, 2018)
It is known that the application of herbicides with residual activity in the soil, such as alachlor, clomazone, S-metolachlor, pendimethalin, and trifluralin, proved to be an efficient alternative to control weedy rice in other production systems (Griffin and Harger, 1990; Askey et al, 1998)
The herbicide factor was significant, and most of the treatments provided a low level of control of the giant arrowhead, except for flumioxazin, which presented a mean control higher than 89% (Table 1)
Summary
In Santa Catarina, paddy rice culture is carried out in two production systems (water-seeded and drill-seeded), covering approximately 80% and 20% of the cultivated area, respectively (Sosbai, 2018). The early preparation of the soil stimulates the germination of weedy rice seeds in the offseason, allowing the adoption of management practices that reduce the infestation of this species during the crop cycle. Another characteristic of the “catarinense” production of water-seeded rice is the lack of crop rotation in the production fields (Eberhardt et al, 2016). 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, the selectivity of this herbicide treatment needs to be studied. 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
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