Weed management in citrus orchards largely involves the application of nonselective herbicides (e.g., glyphosate and paraquat) for postemergence control (Singh et al., 2005). The off-target movement of these herbicides (drift) can affect citrus tree physiology with consequent impact on orchard profitability. It has been reported that the glyphosate contamination of sweet orange (Citrus sinensis) can result in peel burn and fruit drop (Erickson, 1996).
To minimize spray drift from herbicide applications, efforts have been made to develop less drift-prone equipment and application techniques. The most notable technology advances include: low-drift nozzles (Nuyttens et al., 2009), air-assisted boom sprayers (Pichè et al., 2000), drift reduction adjuvants (Johnson et al., 2006), and sprayer shield (Wolf et al., 1993). While the use of drift-reducing technologies has raised concern about potential reduction in herbicide application effectiveness (Knoche, 1994); several authors have reported no reduction in weed control efficacy of glyphosate applications with low-drift nozzles (Etheridge et al., 2001; Wolf, 2000).
Different approaches have been adopted to quantify the drift generated during pesticide applications. Salyani and Cromwell (1992) used high-volume air samplers and polyester film (Mylar®, DuPont, Wilmington, DE) to, respectively, quantify airborne and fallout spray drift from aerial and ground orchard sprayers. In another study, Salyani and Farooq (2004) used vertically hung polyester strings to sample spray drift from various citrus sprayers. Nevertheless, the most widespread method of drift assessment involves sampling of spray deposit at various downwind distances (Ganzelmeier et al., 1995; McArtney and Obermiller, 2008; Van de Zande et al., 2006). In herbicide applications, drift can be monitored by evaluating the injuries on sentinel plants (Felsot et al., 1996). Overall, the above techniques have shown a high variability of deposition in time and space because of the changes in weather conditions (Stover et al., 2003; Van de Zande et al., 2006). It has been difficult to compare different trials without directly comparable and repeatable conditions. Therefore, laboratory procedures have been developed to evaluate the potential drift of nozzles in wind tunnels (Derksen et al., 1999; Herbst 2001; Nuyttens et al., 2009). Wind tunnel may provide a method to classify drift potential of single or multiple nozzles without the effects of sprayer movement, crop characteristics, and environmental conditions. To simplify the test procedure and to reduce trial costs, Balsari et al., (2007) developed the DEIAFA test bench to evaluate drift potential of field crop sprayers. The methodology involves sampling of spray cloud that lingers on after the sprayer pass. Normally, the larger spray cloud mass and longer lingering time associate with greater drift potential under field conditions (Balsari et al., 2007). The main objective of this study was to evaluate the suitability of the DEIAFA drift test bench system in assessing drift potential of a citrus herbicide applicator. Specific objectives of the study were: 1) to develop a computational procedure for the evaluation of deposit values measured with the test bench and 2) to investigate the effects of drift shield, nozzle type, and ground speed on the drift potential of the sprayer.
Balsari, P., Marucco, P. & Tamagnone, M. 2007 A test bench for the classification of boom sprayer according to drift risk Crop Protection 26 1482 1489
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Etheridge, R.E., Hart, W.E., Mayes, R.M. & Mueller, T.C. 2001 Effect of venturi-type nozzles and application volume on post emergence herbicide efficacy Weed Technol. 15 75 80
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Herbst, A. 2001 A method to determine spray drift from nozzles and its link to buffer zone restrictions Amer. Soc. Agr. Eng. Intl. Mtg. Paper No. 01-1047.
Johnson, A.K., Roeth, F.W., Martin, A.R. & Klein, R.N. 2006 Glyphosate spray drift management with drift reducing nozzles and adjuvants Weed Technol. 20 893 897
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Nuyttens, D., Taylor, W.A., De Schampheleire, M., Verboven, P. & Dekeyser, D. 2009 Influence of nozzle type and size on drift potential by means of different wind tunnel evaluation methods Biosystems Eng. 103 271 280
Salyani, M. 2000 Methodologies for assessment of spray deposition in orchard applications Amer. Soc. Agr. Eng. Intl. Mtg. Paper No. 00-1031.
Singh, S., Singh, M. & Futch, S.H. 2005 Effect of application time and glyphosate formulations on weed control efficacy in young citrus groves Proc. Florida State Hort. Soc. 118 62 65
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Stover, E., Scotto, D., Wilson, C. & Salyani, M. 2003 Pesticide spraying in Indian River grapefruit: II. Overview of factors influencing spray efficacy and off-target deposition HortTechnology 13 166 177
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