Doctoral Dissertations

Date of Award

12-1999

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

Thomas C. Mueller

Committee Members

Al Womac, Bob Hayes, Neil Rhodes, Tom Mueller, William Hart

Abstract

Laboratory and field studies were conducted to evaluate the drift potential and efficacy of commonly used postemergence herbicides applied through venturi-type drift reduction nozzles as compared to a standard flat fan nozzle. Laboratory studies were conducted utilizing a Malvem laser droplet/particle size analyzer to determine the droplet spectra produced by a given nozzle. Spray solutions of glufosinate, glyphosate, and paraquat were applied through all combinations of five nozzle types (four venturi), three tip sizes, and four application pressures. Nozzles were also evaluated for pattern uniformity utilizing water plus surfactant at one pressure. When averaged over herbicide, tip size, and pressure the venturi nozzles collectively produced larger volume median diameter droplets than the standard nozzle. The percent of spray volume in droplets < 205 pm 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 volume median diameter. The venturi nozzles were more variable in their spray volume distribution than the standard nozzle.

Field studies were conducted to compare nozzle effects on the efficacy of postemergence herbicides applied to common cocklebur (Xanthium strumarium) and broadleaf signalgrass (Brachiaria platyphylla). Spray solutions of commercial formulations of glufosinate, glyphosate, and paraquat were applied through all combinations of three nozzles (two venturi) and two application volumes. Nozzle type had the most consistent effect on common cocklebur control. The Delavan Raindrop Ultra venturi nozzle provided the least control (≤ 93%) and least biomass reduction (87%). The Spraying Systems AI Teejet venturi nozzle and the Spraying Systems XR Teejet flat fan nozzle provided similar levels of control (94 to 96%) and biomass reduction (92 and 93%). Nozzle type also affected broadleaf signalgrass control, but herbicide had the most consistent effect. Glyphosate controlled broadleaf signalgrass less (≤ 88%) than either glufosinate or paraquat (92 to 98%).

Field studies were conducted to measure nozzle effects on the accuracy of herbicide deposition in a target area and to identify the nozzle parameters responsible for accurate herbicide placement. The Delavan Raindrop Ultra and Spraying Systems AI Teejet venturi nozzles deposited a larger percentage of applied herbicide in the target area than the flat fan nozzle. However, the uniformity of herbicide deposition was similar for the venturi and flat fan nozzles. Increasing application volume increased the uniformity of herbicide deposition in the target area with all nozzles. Correlation analysis indicated that the percentage of spray volume contained in droplets smaller than approximately 200 µm was most important in determining herbicide deposition.

Venturi nozzles produce larger droplets which are less susceptible to drift than droplets produced by conventional flat fan nozzles. However, venturi nozzles vary in the size of droplets produced and the level of weed control they provide. Venturi nozzles which produce droplets of approximately 450 µm can provide weed control similar to that provided by a flat fan nozzle, whereas, venturi nozzles which produce 650 µm droplets provide less weed control than a flat fan nozzle. Venturi nozzles can reduce the drift potential of herbicide sprays and, depending on the specific nozzle, can be as effective as flat fan nozzles with a variety of postemergence herbicides. Due to their overall reduction in drift potential of herbicide sprays, venturi nozzles can provide producers with increased flexibility with respect to the timing and location of herbicide applications. Also, utilization of venturi nozzles will allow producers to tailor herbicide application parameters, such as herbicide choice and application volume, to optimize weed control while minimizing drift potential.

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