Non-Peer ReviewedAs pesticides become more biologically active and their use becomes more widespread the impacts of spray drift become a topic of considerable interest. The drifting of sprays is a complex process; factors influencing it include meteorological conditions, application parameters, and the nature of the target. Advances in aerial application technology and in our ability to measure drift, coupled with the adoption of new technologies for regulating pesticide application spurs a desire for a greater understanding of the pesticide application process. Experiments were conducted to quantify and profile drift from aerial applications of pesticide. The effects of atomizer type, spray quality and ground cover were examined. The materials and methods essential to conduct such a project were reviewed in detail

Caldwell, D.M.

Wolf, T.M.

English

eCommons@USASK

Quantification of spray drift from aerial applications of pesticide

University of Saskatchewan Research Archive

Quantification of Spray Drift fromAerial Applications of PesticideD.M. Caldwell1, and T.M. Wolf21Department of Plant Science, University of Saskatchewan, #51 Campus Dr., Saskatoon, SK,S7N 5A82Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK, S7N 0X2Key Words: Spray Drift, Aerial ApplicationAbstractAs pesticides become more biologically active and their use becomes more widespread theimpacts of spray drift become a topic of considerable interest. The drifting of sprays is a complexprocess; factors influencing it include meteorological conditions, application parameters, and thenature of the target. Advances in aerial application technology and in our ability to measure drift,coupled with the adoption of new technologies for regulating pesticide application spurs a desirefor a greater understanding of the pesticide application process. Experiments were conducted toquantify and profile drift from aerial applications of pesticide. The effects of atomizer type, sprayquality and ground cover were examined. The materials and methods essential to conduct such aproject were reviewed in detail.IntroductionPesticide spray drift is defined as plant protection product carried out of the target area throughthe air during the application process, or shortly thereafter (ISO Draft Proposal, 2003). Theapplied chemicals move down wind of the treated area where they can have a detrimental effecton sensitive plants, wildlife and humans.The drifting of sprays is a complex process. Factors influencing drift include meteorologicalconditions, application parameters, and the nature of the target or other interceptors (Teske,2002).The protection of the environment is a fundamental value of all Canadians. It is important tokeep our air and water free from pollutants. A renewed interest in protecting the environmentfrom pollutants coupled with advances in aerial application technology and in our ability tomeasure drift spurs a desire for a greater understanding of the pesticide application process. Themost recent efforts to quantify drift from agricultural aerial applications of pesticide in Canadawere 25 years ago (Maybank, et al. 1978). Modern applications are made from aircraft withdifferent aerodynamic characteristics and with different atomization technology. The chemicalsapplied today are more target specific, and less toxic to non-target organisms than the onesapplied a quarter century ago. In addition we have adopted new technologies for regulatingpesticide application which have yet to be validated. The above noted reasons necessitate furtherstudy in the area of spray drift.The primary objective for this project was to generate empirical data to quantify spray driftdeposits from fixed wing aerial applications of pesticide. Attempts were also made to profile thespray cloud as it moved down wind of the application area. The data generated from thisexperiment may also prove useful in illustrating the effects of specific application parameters onthe amount of spray deposited downwind. The results of this experiment will be evaluatedagainst the output of the mechanistic models currently used for decision making in the regulatoryprocess.Materials and MethodsThe treatments in this experiment were designed to examine the effects of several applicationparameters. The specific issues of interest in this project include the effects of spray quality,atomization, and ground cover. Application scenarios include Fine vs. Medium spray qualities,deflection vs. rotary atomizers, and application to bare ground vs. to a mature crop canopy.The two spray quality treatments were generated using the same CP 09 nozzle with a deflectionsetting of 0o for the Medium spray quality and a deflection setting of 30o for the Fine sprayquality. The two different atomization treatments included the CP 09 flooding-deflection typenozzle, and the ACS rotary-cage type nozzle. The two ground covers in the experiment were abarley crop in the late stages of anthesis (standing approximately 0.9 m tall) and the bare groundtreatment was a field of peas that had been harvested, leaving very little residue on the surface.Each treatment in the experiment was replicated three times. This project was designed as afractional factorial experiment, whereby the effect of one particular treatment can only beexamined with respect to that application parameter. It was not logistically feasible to design afactorial experiment with enough treatments where one application parameter could be evaluatedas influenced by another. All treatments were made with an Air Tractor AT502, applying a tankmix of Rotamine-WT tracer dye, Ag-surf surfactant and an optical brightener.Table 1. Application scenarios evaluated.Trt Atomizer Spray Quality Target1CP 090o MediumMatureCereal2CP 0930o FineMatureCereal3ACSRotary FineMatureCereal4CP 0930o FineBareGroundThe northern third of a field measuring approximately 600m by 1600m was used as theexperimental site. The flight path was marked off perpendicular to the wind direction on thewindward side on the field. Three parallel sampling lines were marked perpendicular to the flightpath. Sampling stations for drift measurement were placed at 12.5m, 25m, 50m, 100m, 200m andDistance (m2)12.5 25 50 100 200 400Deposit (µg/m2)0.1110100100010000Trt #1Reg #1Trt #2Reg #2Trt #3Reg #3Trt #4Reg #4 Distance (m2)12.5 25 50 100 200 400Deposit (µg/m2)110100100010000100000Trt #1Reg #1Trt #2Reg #2Trt #3Reg #3Trt #4Reg #4 Figure 1. Deposition on the passive samplers at ground level. Petri-dish deposition isshown on the right and straw deposition on the left.400m on each of the sampling lines. The off-swath samples were placed at these stations.Stations were also placed directly on the flight path and upwind of the application area, the on-swath samples and check samples were placed at these respective stations.Samplers utilized in this experiment simulated both vertical and horizontally oriented targets.The horizontal samplers were 15-cm diameter petri dishes placed at each sampling stations. Thevertical samplers were plastic drinking straws 0.6cm in diameter and 12cm long. These were alsoplaced at each sampling station. Plastic strings sampled the spray cloud with height. The stringswere suspended by helium blimps elevated to a height of 30m. The strings were 2mm indiameter and processed in 1m sections. Blimps were placed at the 25m, 100m and 400m stations.Rotorod towers actively sampled the spray cloud at a rate of 120L per minute. The towerssampled the air at 1m, 2m, 3m, and 4m. A pair of rotorod towers was placed at the 25m, 100mand 400m stations.In order to account for the photolytic break down of the tracer dye in ultra violet light, severalsamples were sprayed with dye prior to the experiment and stored in the dark. These were placedupwind of the treatment area in direct sunlight during the course on the spray application.Once the pesticide application had been made the samplers were collected in a sanitary mannerand placed into dark storage. In order to prevent contamination of the samples, care was taken toensure off-swath samples were not handled near or stored with the on-swath samples. Sampleswere processed by washing in ethanol. The wash was collected and its dye concentration wasdetermined on a fluorescence spectrophotometer. The fluorescence spectrophotometer measuredthe fluorescence intensity of the wash solution and the concentration of dye in the solution wasdetermined by comparison to standard solutions. Dye concentrations from the fluorescencespectrophotometer were expressed as parts per billion.The wash concentrations from the fluorescence spectrophotometer were then converted to µg ofthe dye deposited per unit area. These conversions were made based on the concentration of thedye in the spray tank solution, surface area of the sampling device, volume of ethanol used towash the sampling device, photolytic multipliers, and the conversion of ppb to µg or % of theactual amount applied.Preliminary ResultsStatistical analysis has not yet been conducted on the data at the time of publication but graphs ofthe data reveal some preliminary results of the experiment (Figure 1). The data for deposition onFigure 2. String deposit with elevation for theCP 09 30o treatmentDeposit (mg/m2)0.0 2.0 4.0 6.0 8.0 10.0 12.0Height (m)05101520253025m vs Height 100m vs Height the targets at ground level was linear once plotted on a log-log scale. While definitive statementsregarding treatment differences cannot be made yet, the results do seem to illustrate some of theexpected trends for spray drift. For example, the deposition down wind on the first treatment (theMedium spray quality) seems to be less than the deposition for the second treatment (the Finespray quality). Another expected trend illustrated in the data is the greater deposition of driftingspray on the vertically oriented compared to horizontally oriented targets. The graph fordeposition on the drinking straw samplers show greater deposition per unit surface area than onthe petri dishes by about one order of magnitude. This demonstrates the superior ability of thissampler to collect airborne drift deposits.The data collected from the string and rotorod samplers will be more challenging to analyze andinterpret than the deposition data. Specific attributes of the data set will have to be identified inorder to allow for statistical analysis. The graphical images of these data sets help demonstratethe typical processes which occur as the spray cloud moves downwind. At short distancesdownwind of the application the spray cloudtended to be heavily concentrated near theground level (Figure 2). As the cloud movedfurther down wind some of its particles weredeposited onto the ground, and some of thecloud was dispersed to higher elevations.The result was a spray cloud that wasincreasing in size and decreasingconcentration as it moved down wind.Future work on this project will involvedetailed analysis of the meteorologicalconditions measured during the applications.A comprehensive statistical analysis of driftdeposits on each type of sampler will also beconducted. Finally an empirical model willbe developed which can compared to theoutput of computer models currently used inthe regulatory process.ConclusionsThis project has generated a valuable data set that has great potential to increase ourunderstanding of pesticide drift. Its analysis can shed new light on an area of study that has notbeen looked at in some time. The results of this project can help not only to mitigate the damagescaused by spray drift but also provide a level of confidence with the mechanistic modelscurrently used in the regulatory system.Acknowledgements:We would like to extend our thanks to Brian Caldwell, Skye Ketilson, Lorelei Gress and DaveCote for their technical support. We thank Ted Kuchnicki, Derek Francois, JD Whall for theirassistance in conducting the trials. We would also like to thank Blair Mutcher and the staff fromLonesome View for their assistance with the applications. Thanks also to Guy Lafond foraccommodating us at the Indian Head research farm and to the Qu’Appelle Valley PlowsharesInitiative for donating land for the trial.Literature CitedISO Draft Proposal. 2003. Equipment for crop protection - Methods for the field measurement ofspray drift.Maybank, J., Yoshida, K., and Grover, R. 1978. Spray drift from aerial pesticide applications.APCA Journal 28(10):1009-1014Teske, M.E., Bird, S.L., Esterly, D.M., Curbishley, T.B., Ray, S.L., and Perry, S.G. 2002.AgDRIFT: a model for estimating near-field spray drift from aerial applications. EnvironmentalToxicology and Chemistry.  21(3):659-671.

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Quantification of spray drift from aerial applications of pesticide

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