The aim of this research was to evaluate the effect of night-time application on the reduction of spray volume and dose rate in post-emergence herbicide applications and on the selectivity to soybean plants. Two field trials were settled in the experimental farm of the FCAV/UNESP - Jaboticabal/SP, Brazil, during 1994/95 and 1995/96. Spray applications were carried out at 5:00 and 9:00a.m. and 2:00, 5:00 and 10:00p.m. In the first trial the herbicides lactofen and bentazon were applied at 60% of the recommended rate. In the second trial lactofen was applied at 40% of the standard rate and fomesafen at 70%. Control plots were treated with the recommended rate of the herbicides. There were also settled weeded and unweeded plots. It was verified that the reduced dose and spray volume applications carried out at 5:00 a.m. and 10:00 p.m. favored the performance of lactofen with 60% of the standard rate but the contrary ocurred with fomesafen. There was no statistical difference between spray volumes studied which allowed the application of 75 or 150l/ha according to the most favorable period for each herbicide. The effect of herbicides bentazon, lactofen and fomesafen depends, besides the environmental conditions during the night-time, on the interations with these herbicides and the weeds.
spray volume; reduced rate; bentazon; lactofen; fomesafen