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Understanding Spray Drift

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    1. Understanding Spray Drift Robert E. Wolf Extension Specialist

    3. Nozzle Technology? Nozzles designed to reduce drift Improved drop size control Emphasis on Spray Quality Beginning with the extended range flat fan nozzle (all major manufactures have one), continuing with the design of preorifice inserts and turbulation chambers, and now with the venturi style nozzle design, nozzle manufacturer's have worked to develop nozzles that are improving the quality of spray emitted. Beginning with the extended range flat fan nozzle (all major manufactures have one), continuing with the design of preorifice inserts and turbulation chambers, and now with the venturi style nozzle design, nozzle manufacturer's have worked to develop nozzles that are improving the quality of spray emitted.

    4. Nozzles are important: Control the amount GPA. Determine uniformity of application. Affects the coverage. Influences the drift potential.

    5. Will affect drift: Movement of spray particles off-target. Creating smaller spray drops will result in increased drift. Is it Coverage vs Drift? What is the answer?

    6. Technical Aspects of Spray Drift

    7. Definition of Drift: Movement of spray particles and vapors off-target causing less effective control and possible injury to susceptible vegetation, wildlife, and people. Adapted from National Coalition on Drift Minimization 1997 as adopted from the AAPCO Pesticide Drift Enforcement Policy - March 1991

    8. Types of Drift: Vapor Drift - associated with volatilization (gas, fumes) Particle Drift - movement of spray particles during or after the spray application

    9. Factors Affecting Drift: Spray Characteristics chemical formulation drop size evaporation

    10. Wind Direction: Wind direction is very important Know the location of sensitive areas - consider safe buffer zones. Do not spray at any wind speed if it is blowing towards sensitive areas - all nozzles can drift. Spray when breeze is gentle, steady, and blowing away from sensitive areas. Dead calm conditions are never recommended.

    11. Because: Light winds (0-3 mph) tend to be unpredictable and variable in direction. Calm and low wind conditions may indicate presence of a temperature inversion. Drift potential is lowest at wind speeds between 3 and 10 mph (gentle but steady breeze) blowing in a safe direction. However, Drift Potential May be High at Low Wind Speeds

    12. Spray Droplet Movement with Various Wind Speeds The information presented on this slide demonstrates the effects of wind on the spray droplets. Note that the distances the droplets move are dramatically higher with the smaller droplets. As the droplet sizes increase, the distances moved decreases. Thus, larger spray droplets have a far greater opportunity to deposit on the target area. The information presented on this slide demonstrates the effects of wind on the spray droplets. Note that the distances the droplets move are dramatically higher with the smaller droplets. As the droplet sizes increase, the distances moved decreases. Thus, larger spray droplets have a far greater opportunity to deposit on the target area.

    13. Wind Speeds Gradients This diagram shows that as the height above the ground or the crop increases the velocity of the wind increases. This is a natural phenomenon.This diagram shows that as the height above the ground or the crop increases the velocity of the wind increases. This is a natural phenomenon.

    14. Wind Current Effects Wind currents can drastically affect spray droplet deposition Structures drastically affect wind currents Wind breaks Tree lines and orchards Houses and barns Hills and valleys Wind and air currents can drastically affect spray droplet deposition. When the wind blows against structures, the direction of the wind currents can be drastically affected. In this discussion, structures will be used to define anything that can deflect wind flow. Wind and air currents can drastically affect spray droplet deposition. When the wind blows against structures, the direction of the wind currents can be drastically affected. In this discussion, structures will be used to define anything that can deflect wind flow.

    15. Wind Patterns Near Shelterbelts This diagram shows the effects of a shelterbelt or tree line on the wind and the resulting currents developed. Note that on the upwind side of the trees the winds are flowing along in a laminar manner. As the currents approach the trees, the atmospheric pressure rises and the deflection of the wind currents begins. While most of the wind currents are deflected over the top of the trees, some of the currents are trapped in the trees. On the downwind side, there is a turbulent area and a relatively calm area. This describes how spray droplets are often moved by wind currents to unexpected areas-i.e., symtomology may be observed at the tops of trees as well as areas near the ground. This diagram shows the effects of a shelterbelt or tree line on the wind and the resulting currents developed. Note that on the upwind side of the trees the winds are flowing along in a laminar manner. As the currents approach the trees, the atmospheric pressure rises and the deflection of the wind currents begins. While most of the wind currents are deflected over the top of the trees, some of the currents are trapped in the trees. On the downwind side, there is a turbulent area and a relatively calm area. This describes how spray droplets are often moved by wind currents to unexpected areas-i.e., symtomology may be observed at the tops of trees as well as areas near the ground.

    16. Wind Patterns Near Treelines This diagram of wind currents has several applications. If there was a field between two tree lines then the turbulent and circular flows described could result in spray droplet deposition even in upwind areas bordering the field If the sketch was depicting level fields with a ditch or depression, then one could understand how product was moved down into the depression by wind currents. Areas with topographical variability-i.e, a combination of hills, valleys, woodlands-can present even greater variables which result in spray droplet deposition in areas that would be difficult to explain without these diagrams. This diagram of wind currents has several applications. If there was a field between two tree lines then the turbulent and circular flows described could result in spray droplet deposition even in upwind areas bordering the field If the sketch was depicting level fields with a ditch or depression, then one could understand how product was moved down into the depression by wind currents. Areas with topographical variability-i.e, a combination of hills, valleys, woodlands-can present even greater variables which result in spray droplet deposition in areas that would be difficult to explain without these diagrams.

    17. Wind Patterns Around Buildings This diagram and the following one describe the flow of winds around a building or similar structure. Notice how the air swirls toward the ground on the downwind side of the building. Drifting fine droplets could easily be deposited here.This diagram and the following one describe the flow of winds around a building or similar structure. Notice how the air swirls toward the ground on the downwind side of the building. Drifting fine droplets could easily be deposited here.

    18. Wind Patterns Around Buildings This overhead sketch of the wind currents around a building show how the swirling currents would allow the deposition of drifting fine droplets. This overhead sketch of the wind currents around a building show how the swirling currents would allow the deposition of drifting fine droplets.

    20. Inversions:

    21. Temperature Inversions:

    22. Recognizing Inversions: Under clear to partly cloudy skies and light winds, a surface inversion can form as the sun sets. Under these conditions, a surface inversion will continue into the morning until the sun begins to heat the ground.

    24. Precautions for Inversions: Surface inversions are common . Be especially careful near sunset and an hour or so after sunrise, unless There is low heavy cloud cover The wind speed is greater than 5-6 mph at ground level 5 degree temp rise after sun-up Use of a smoke bomb or smoke generator is recommended to identify inversion conditions.

    25. Spray Droplet Size

    26. Efficacy and Drift Potential is Influenced by: Size of the Spray Droplets - Volume Median Diameter (VMD) Droplet Spectrum (Range - big to small)

    27. Relationship of Drift to Drop Size

    28. Comparison of Micron Sizes for Various Items: (approximate values) pencil lead 2000 (?m) paper clip 850 (?m) staple 420 (?m) toothbrush bristle 300 (?m) sewing thread 150 (?m) human hair 100 (?m)

    30. Cutting Droplet Size in Half Results in Eight Times the Number of Droplets

    31. Important Droplet Statistics:

    32. Evaporation of Droplets

    33. Spray Characteristics are Important to Understand:

    35. New Label language-EPA Reviewing Public Comments Public Listening Sessions planned Sometime in 2003?? Match the crop protection product to the target Adhere to label guidelines based on an industry standard ASAE S-572 Buffer Zones or No Spray Zones Maximize Efficacy Minimize Drift EPA Requested Changes Coming!!!!

    36. Origin Of Standardized Spray Droplet Size Categories 1985 -- British Crop Protection Council (BCPC) Droplet size classifications, primarily designed to enhance efficacy. Uses the term SPRAY QUALITY for droplet size categories. 2000 -- ASAE Standard S572 Droplet size classifications, primarily designed to control spray drift. Uses the term DROPLET SPECTRA CLASSIFICATION for droplet size categories.

    37. ASAE DSC and Volume Median Diameter (DV0.5) From PMS* Laser Spectrometer Very Fine (VF) < 182m Fine (F) 183-280m Medium (M) 281-429m Coarse (C) 430-531m Very Coarse (VC) 532-655m Extremely Coarse (XC) >656m These size categories are developed from an ASAE standard reference nozzle set with a laser instrument. Spray nozzles and their operational parameters must then be characterized by the same laser instrument. The DSC categories from VF to XC are from the ASAE standard, the size ranges were obtained with the USDA ARS PMS system at College Station, Texas. Other instruments may give slightly different droplet size ranges with the respective DSC, but it is expected that a different laser system would give the same DSC for the same spray spectrum when the reference nozzles have been used to develop the droplet size ranges for each DSC with that different laser system and that system is in turn used to classify the DSC of the given spray spectrum. The standard requires that the same system be used for classifying nozzles that is used for establishing the size categories with the ASAE standard reference nozzle set. These size categories are developed from an ASAE standard reference nozzle set with a laser instrument. Spray nozzles and their operational parameters must then be characterized by the same laser instrument. The DSC categories from VF to XC are from the ASAE standard, the size ranges were obtained with the USDA ARS PMS system at College Station, Texas. Other instruments may give slightly different droplet size ranges with the respective DSC, but it is expected that a different laser system would give the same DSC for the same spray spectrum when the reference nozzles have been used to develop the droplet size ranges for each DSC with that different laser system and that system is in turn used to classify the DSC of the given spray spectrum. The standard requires that the same system be used for classifying nozzles that is used for establishing the size categories with the ASAE standard reference nozzle set.

    39. Computer Models:

    40. AgDRIFT Program Map

    41. Example of Model Use - Aerial: Applicators Standard Operation

    42. Strategies to Reduce Drift: Select nozzle to increase drop size Increase flow rates - higher application volumes Use lower pressures Use lower spray (boom) heights Avoid adverse weather conditions Consider using buffer zones Consider using new technologies: drift reduction nozzles drift reduction additives shields, electrostatics, air-assist

    43. Some Other Things to Keep in Mind when Planning a Spray Application Allow enough time for: Scheduling and planning the application Obtaining the products Setting up the application date Weather delays or maintenance problems, if necessary.

    44. In Conclusion: