Graduate Thesis Or Dissertation
 

The role of droplet size, concentration, spray volume, and canopy architecture in herbicide application efficiency

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  • To improve the efficiency of herbicide applications, each stage of the spray application process must be considered. Two of these stages, the process of spray deposition within plant canopies and the influence of the form of the spray deposit on efficacy were investigated. The effect of droplet size, spray volume, and droplet trajectory on the vertical distribution of spray deposits was measured within canopies of bracken fern (Pteridium aquilinum L. Kuhn) and greenleaf manzanita (Arctostaphylos patula Greene). Spray containing a fluorescent tracer was applied using spinning disc and flat fan nozzles, and deposition was measured on horizontal strings placed at various levels in the canopy. Spray deposition profiles were not significantly affected by droplet size. With bracken, 50 1/ha application volumes gave greater deposition than at 100 1/ha. Spray deposition was increased, particularly with the vertically oriented manzanita foliage, when droplets entered the canopy with a significant horizontal component to their trajectory. The foliage structure of bracken and manzanita canopies was measured using a point quadrat vegetation sampling technique. A model to predict spray deposition profiles was then developed, and observed deposition profiles were compared to predicted profiles. With bracken, the modelled profile was close to, but underestimated, the measured deposit attenuation. With manzanita, the predicted deposit profile overestimated deposit attenuation, suggesting that the vertically moving droplets were reflected from the foliage inclined at 72° from the horizontal. The effects of droplet size, spray volume, and herbicide rate on phytotoxicity were also investigated. Glyphosate and fluroxypyr were applied to bracken fern and greenleaf manzanita, respectively, using spinning discs. Increasing glyphosate concentration or the area of foliage wetted were equally effective in enhancing efficacy on bracken fern. A smaller droplet size and higher spray volume increased the efficacy of fluroxypyr on manzanita. For both species and chemical combinations, the addition of a surfactant, L-77, showed the greatest potential for increasing the efficiency of spray applications. In general, using small droplets with a horizontal velocity component, and a suitable surfactant will increase spray efficiency. High herbicide concentrations may be beneficial if localized scorch does not occur.
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Déclaration de droits
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  • Master files scanned at 600 ppi (256 Grayscale) using Capture Perfect 3.0.82 on a Canon DR-9080C in TIF format. PDF derivative scanned at 300 ppi (256 B&W), using Capture Perfect 3.0.82, on a Canon DR-9080C. CVista PdfCompressor 4.0 was used for pdf compression and textual OCR.
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