Water regime and straw influence on the effectiveness of preemerging herbicides without control of sourgrass?

Abstract

The control of sourgrass, has been one of the great challenges in the soybean culture, and the pre-emergent herbicides appear as a management option. The objective of this work was to evaluate the control of sourgrass using pre-emergent herbicides positioned under different irrigation regimes and amounts of straw. Two experiments were carried out, the first with corn straw + Urochloa ruziziensis (0 and 3 t ha(-1)) and the second without straw, both in a greenhouse with a completely randomized design in a 6 x 3 factorial scheme, in the first factor irrigation regimes (initial of 5 mm and after 48 hours 10 mm for maintenance, initial of 20 mm and after 48 hours 10 mm for maintenance, initial of 5 mm and after, 5, 10, 15 or 20 days a rain of 20 mm) and in the second, the pre-emergent herbicides: (diclosulam (29.4 g i.a ha(-1)); flumioxazin + imazethapyr (50 + 106 g i.a ha(-1)) and diuron + sulfentrazone (420 + 210 g i.a ha(-1)). When applied directly to the soil and on straw, diclosulam showed the lowest percentages of control in all irrigation regimes with the first rain of 5 mm and the second of 20 mm. Diuron + sulfentrazone and flumioxazin + imazethapyr did not present significant differences in the irrigation regimes, effectively controlling the sourgrass. The effectiveness of diclosulam was influenced by drought intervals after application, diuron + sulfentrazone and flumioxazin + imazethapyr showed an effective control of sourgrass in all treatments.