All previous studies reporting the application time-of-day effect for herbicides have been conducted with a single-orifice, flat fan nozzle. Whether an increased number of flat fans in the nozzle could affect the application time-of-day effect is unknown. A replicated outdoor pot experiment was conducted to determine the best application time for trifloxysulfuron from 05:00 (before sunrise), 07:00 (after sunrise), 09:00, 11:00, 13:00, 15:00, 17:00, 19:00 (before sunset), and 21:00 (after sunset) against velvetleaf when sprayed with a single-, dual-, or triplet-orifice flat fan nozzle. Trifloxysulfuron sprayed with the single-orifice flat fan nozzle at 05:00 was the least effective treatment reducing velvetleaf fresh weight by 51%. When the single-orifice flat fan nozzle was used, velvetleaf fresh weight, expressed as a quadratic polynomial function with a parabola opening upward, decreased as the application time changed from 05:00 to 11:00 (70% control); thereafter, it increased until 21:00. When the dual- and triplet-orifice flat fan nozzles were used, velvetleaf fresh weight, expressed as a quadratic polynomial function with a parabola opening downward, increased from 05:00 to 07:00; thereafter, it increased as the application time changed until 19:00 (the best application time, reducing velvetleaf fresh weight by 82%). Foliar nyctinasty in velvetleaf is responsible for decreased efficacy of trifloxysulfuron sprayed with the single-orifice flat fan nozzle before sunset. This obstacle can be overcome using the dual- or triplet-orifice flat fan nozzles.
