Laboratory studies were conducted using a Malvern laser droplet/particle size analyzer to determine the droplet spectra of several venturi-type drift reduction nozzles compared to a standard single, elliptical-orifice flat fan nozzle. Spray solutions of glufosinate, glyphosate, and paraquat were applied through all combinations of five nozzle types (four drift reduction), three tip sizes, and four application pressures. Nozzles were also evaluated for pattern uniformity using water plus surfactant at one pressure. When averaged over herbicide, tip size, and pressure the venturi nozzles collectively produced larger volume median diameter (VMD) droplets than the standard nozzle. The percentage of spray volume in droplets < 205 μm was less for the venturi nozzles (17%) than for the standard nozzle (65%) when averaged across all factors. The order of herbicides producing the largest droplets was paraquat (470 μm) > glyphosate (460 μm) > glufosinate (400 μm), as measured by VMD. The venturi nozzles were more variable in their spray volume distribution than the standard nozzle. Utilization of venturi-type nozzles may minimize the drift potential of the herbicides evaluated but could also lead to uneven herbicide application and subsequent erratic weed control.

Field studies were conducted to compare venturi-type nozzles to a fan nozzle with respect to the efficacy of postemergence herbicides applied to common cocklebur and broadleaf signalgrass. Spray solutions of glufosinate, glyphosate, and paraquat were applied through all combinations of three nozzles and two application volumes. Venturi nozzles were a Delavan Raindrop Ultra (RU) and a Spraying Systems AI Teejet (AI). A Spraying Systems XR Teejet (XR) fan nozzle was included as a standard. Previous work indicated droplet size spectra differed among these nozzles. There was a difference in common cocklebur control among nozzles (AI = XR > RU), although control was at least 90% for all nozzles. Herbicide choice had a greater effect on broadleaf signalgrass control than nozzle type. Broadleaf signalgrass control differed among herbicides (glufosinate = paraquat > glyphosate) and among nozzles (AI = XR > RU). Herbicide performance varied between nozzles (AI > RU), but the AI nozzle was as effective as the XR fan nozzle.

No abstract

Field studies were conducted in 1993 and 1994 to evaluate sicklepod control with combinations of imazaquin + metribuzin at lower than normal use rates. Soybean was seeded in late-May to early-June each year and imazaquin and metribuzin were applied PPI alone at 0.75 and 1x and 0.5, 0.75, and 1x their registered rates, respectively, and in factorial combinations of their 0.5 and 0.75x rates. The registered (1x) rates for imazaquin and metribuzin on this soil type are 0.14 and 0.43 kg/ha, respectively. Several standard sequential treatments and flumetsulam + trifluralin PPI at 0.06 + 0.70 and 0.07 + 0.95 kg/ha were included for comparison. Sicklepod control and soybean seed yield responses differed between 1993 and 1994. In 1993, the combinations of imazaquin + metribuzin averaged 90% control 6 wk after planting (WAP) and soybean seed yield increased 75% compared to the untreated check. Imazaquin + metribuzin at their respective 0.5x rate was as effective as any treatment evaluated. In 1994, sicklepod control was generally lower with all treatments. Soybean seed yield was reduced due to sicklepod interference with soil-applied treatments alone. However, imazaquin + metribuzin at their respective 0.75x rate provided sicklepod control levels and reductions in weed biomass similar to those observed with flumetsulam + trifluralin at 0.07 + 0.95 kg/ha and the sequential treatments, and increased soybean seed yield 19% compared to the untreated check.