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.

In an attempt to refine calibration procedures for greenhouse spray chambers, the effects of an herbicide adjuvant, operating pressure, and travel speed on the static and dynamic spray patterns of single flat-fan hydraulic nozzle tips were studied. The volume output in the central 15 cm of the spray pattern (where target plants would ordinarily be positioned) was used as an indicator of the relative dosages received from both a tapered flat-fan tip (8001 VS) and an even-spray tip (8001 EVS). All tested variables significantly altered the spray pattern. Specifically, dynamic spray patterns differed from static patterns, and speed of travel affected the dynamic pattern for both tapered and even flat-fan sprays. Increasing the travel speed from 0.375 to 0.75 m/s reduced spray deposit in the central 15 cm of the spray pattern by up to 19% for water, and by up to 34% for water containing 0.1% v/v nonionic surfactant. Increasing surfactant concentration to 1% decreased the magnitude of the speed effect. Higher pressure sprays tended to reduce the effect of increased travel speeds. These results show that changes in physicochemical properties of the spray solution as well as air turbulence introduced by nozzle movement can affect the pesticide dosage to which a target plant is exposed in a spray chamber. For proper treatment comparison, delivery systems for greenhouse spray experiments should be calibrated with end-use spray liquids, operating pressures, and nozzle travel speeds.

The importance of spray retention to the biocontrol of green foxtail with Pyricularia setariae was characterized using airbrush and broadcast sprayers at variable application volumes. Spray retention was determined by measuring amounts of a tracer dye solution on treated plants using fluorescence spectrophotometry. Depending on the droplet size, broadcast spraying at 1,000 to 2,000 L/ha produced a level of retention equivalent to that of airbrush spraying until runoff. The trend of P. setariae spore retention on green foxtail was similar to that of liquid retention. Broadcasting P. setariae at volumes producing equivalent spray retention to that of airbrush inoculation resulted in a similar level of weed control under greenhouse conditions. Reducing broadcast volume from 2,000 to 250 L/ha lowered biocontrol efficacy only slightly, when the concentration of P. setariae was increased proportionally to keep the applied fungal dose the same. A nozzle with a fine droplet spectrum (volume median diameter [VMD] 207 μm) had a significantly greater retention efficiency than a coarse spray (VMD 325 μm), but this retention difference was not translated into consistent enhancement of biocontrol efficacy. Higher retention increases may be necessary for more substantial improvement in biocontrol of green foxtail by P. setariae.

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.

Herbicide efficacy, coverage, and retention were evaluated for spray applied through Drift Guard, Turbo TeeJet, AI TeeJet, and TurboDrop drift-reducing nozzles compared to a conventional flat-fan nozzle. Percentage spray coverage detected on water-sensitive cards was greater for conventional and Drift Guard nozzles than for Turbo TeeJet, AI TeeJet, and TurboDrop nozzles. Spray without adjuvants was retained better by redroot pigweed for treatments applied with conventional and Drift Guard nozzles than Turbo TeeJet, AI TeeJet, and TurboDrop nozzles. However, spray with adjuvants was retained similarly for all nozzle types when averaged over spray adjuvant and two weed species. The efficiency of spray retention was greater for spray applied in 47 than in 190 L/ha spray volume for all nozzles. Paraquat and glyphosate, representing contact and translocated herbicides, respectively, provided similar grass species control for all nozzle types, regardless of spray volume. Paraquat and glyphosate were also equally or more effective in 47 compared to 190 L/ha spray volume.

Field experiments were conducted to evaluate the effect of five spray-nozzle types and three drift-control adjuvants (DCA) on glyphosate spray drift. The extended-range (XR) flat-fan nozzle at 280 kPa was used as the standard comparison. DCAs were evaluated for drift reduction with the use of the XR and air-induction (AI) nozzles. Wind speed ranged from 1.3 to 9.4 m/s (3 to 21 mph). Lethal drift (DL) and injury drift (DI) were determined by downwind visual observation of grain sorghum response. Drift distances were measured from the spray swath edge. The Turbo FloodJet and AI nozzles reduced DL distance by 34%. All four drift-reducing (DR) nozzles reduced DI distance by 22 to 32%. Reducing the pressure of the XR flat-fan nozzle from 280 to 140 kPa did not reduce DL or DI distance. When applied through AI nozzles, each DCA increased droplet volume diameter, one DCA reduced DI distance and none reduced DL distance when applied through XR tips. The DCAs did not affect DL or DI distance.

Utility adjuvants are adjuvants that are tank-mixed in the spray solution to improve the spray application process, but do not directly influence herbicide efficacy. However, by improving the spray application process, utility adjuvants can indirectly improve herbicide efficacy. There are five primary utility adjuvant types: compatibility agents, deposition agents, drift control agents (sometimes referred to as antidrift agents or drift retardants), defoaming agents, and water conditioning agents, and three secondary utility adjuvant types: acidifying agents, buffering agents, and colorants (dye markers). Herbicides can react either physically or chemically with other spray mixture components to form an unsprayable mixture. Compatibility agents prevent these reactions from occurring. Drift control agents and deposition agents increase the amount of herbicide deposited on target surfaces. The primary function of drift control agents is to reduce the amount of spray solution that moves off-target. Indirectly, the amount of herbicide reaching target surfaces can be increased. A defoaming agent will reduce or prevent foam produced in the spray mixture. Ions in the spray solution can interact with various herbicides, decreasing efficacy. Water conditioning agents will counteract the effect of the ions on herbicides. Water conditioning agents must be added before the herbicide to prevent herbicide–ion interaction. Acidifying and buffering agents function in a similar fashion, reducing or increasing spray solution pH. A buffering agent will maintain a pH range, whereas an acidifying agent will not. Colorants are dyes that are added to the spray solution to produce a visible color on the sprayed area to assist the applicator in applying the herbicide.

Field experiments were conducted to determine the influence of nozzle type, spray volume, and adjuvants on herbicide efficacy. Carfentrazone and imazamox, representing contact and translocated herbicides, respectively, were equally or more effective when applied with drift-reducing TurboDrop or Drift Guard nozzles than the conventional flat-fan nozzle in 95% of the comparisons. Imazamox was equally effective when applied in 47, 94, or 190 L/ha spray volume, regardless of nozzle type or adjuvant. Carfentrazone applied in 47 L/ha spray volume controlled flax and sunflower as well as in 94 or 190 L/ha, provided urea ammonium nitrate fertilizer and either nonionic surfactant or methylated vegetable oil were included in the spray mixture. Conversely, carfentrazone with only urea ammonium nitrate was less effective when applied in 47 than in 94 or 190 L/ha spray volume. Carfentrazone and imazamox applied in low spray volumes (47 L/ha) gave consistent control when an effective adjuvant was included in the spray mixture.

A field study was conducted in 1992 and 1993 to identify the spray volume and droplet size combinations to optimize control of common cocklebur (Xanthium strumarium) from acifluorfen by maximizing target deposition. In many instances, acifluorfen controlled common cocklebur better using either small (250 µm) or large (450 µm) spray droplets when applied at the lower carrier volumes of either 56 or 112 L/ha. When sprays were applied at 169 L/ha, there was little difference in control between droplet sizes. Deposition of acifluorfen was determined in 1993. Stepwise regression indicated that acifluorfen deposition amount is less important than environmental conditions for common cocklebur control. Relative humidity was the most significant variable for determining common cocklebur control with acifluorfen.