7 Factors Affecting Drift Spray CharacteristicsEquipment & Application HerbicideNozzle type FormulationNozzle size AdditivesNozzle orientation Drop sizeNozzle pressure EvaporationHeight of release
8 Weather & other Factors Affecting Drift Temperature & humidity Wind (direction and velocity) Air stability/inversions Topography
9 Drift Potential Depends on The percentage of small droplets in the droplet size range. Droplet size is measured in microns. The key factor is the percentage of the spray droplets less than 200 microns in diameter.
10 Droplet Size Spray drift droplets are measured in microns and expressed as Volume Median Diameter or VMD One micron = 1/25,000 th inch
12 1/2 of spray volume = larger droplets VMD 1/2 of spray volume = smaller droplets
13 Cutting Droplet Size in Half Results in Eight Times the Number of Droplets = = 2 more droplets fill in the sphere 500 Microns 500 Microns 250 Microns
14 Important Droplet Statistics: Operational Area
15 Evaporation and Deceleration of Various Size Droplets* Droplet Diameter (microns) Terminal Velocity (ft/sec) Final Drop diameter (microns) Time to evaporate (sec) Deceleration distance (in) 20.0470.3<1 50.25171.83 100.913379 1501.75016 2002.4672925 *Conditions assumed: 90 F, 36% R.H., 25 psi., 3.75% pesticide solution
16 SizeVery Fine MediumCoarseVery Coarse Dv0.1<55*55-9495-164165-225>225 Dv0.5<119119-216217-353354-464>464 Dv0.9<204204-369370-598599-789>789 %<14157.220.2-57.25.7-20.12.9-5.6<2.9 *Numbers listed are in Microns Nozzle Drop Size Classification British Crop Protection Council (BCPC)
17 Drop Size Classification & Use Very Fine Fine Medium Coarse Very Coarse <119 m 119-216 m 217-353 m 354-464 m >464 m Insecticides and Fungicides Herbicides and Postemergence Soil Applications of Herbicides
18 http://apmru.usda.gov/downloads/downloads.htm Software for estimating droplet size distribution is available on the web.
Evaporation of Droplets Wind High Relative Humidity Low Temperature Low Relative Humidity High Temperature Fall Distance
20 Wind 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. Spraying in dead calm conditions is never recommended.
21 Drift Potential May be High at Low Wind Speeds 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.
22 Conditions Where are what are the adjacent crops? Are there houses, a town or other sensitive areas near the site?
23 Buffer Zone A buffer zone means an area where pesticide is not directly applied thereby providing protection to a defined area. Buffer zones may depend on: state regulations pesticide product labels prevailing weather conditions sensitive/protected area(s)
24 Product Selection You may have several options on products. Understand the product chemistry! Consider the effect this product may have on homes and gardens near the application site. Consider environmental and wildlife safety.
25 Equipment Selection and Setup Select equipment to produce the largest droplet size possible and still provide adequate coverage. Be aware that some products require relatively smaller droplets to ensure good coverage.
26 When Planning a Spray Application Allow enough time for planning and executing the operation. Including weather and equipment delays. Do not fall into the trap of declaring “I need to spray right now!”. Forcing a job under poor conditions almost always leads to drift or other errors.
27 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.
28 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
Spray Droplet Movement with Various Wind Speeds
30 NameFeaturesCost* DwyerFloating Ball15.50 Wind WizardMechanical39.50 Turbo MeterWind speed - knots, feet/min, meters/sec, mph135.00 Kestrel 1000Maximum, average, current wind speed - knots, feet/min, meters/sec, mph 89.00 Kestrel 2000Maximum, average, current wind speed, temp, wind chill- knots, feet/min, meters/sec, mph 119.00 Kestrel 3000All wind speed features plus temp, wind chill, dew point, heat index, relative humidity 159.00 Plastimo Iris 50**Compass89.00 Wind Meters and Compass *Prices for Wind Meters taken from Gempler’s 2000 Master Catalog **Plastimo Airguide Inc., 1110 Lake Cook Road, Buffalo Grove, IL 60089(708-215-7888)
31 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.
32 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.
33 Nozzles are important Control the amount – GPA. Determine uniformity of application. Affects the coverage. Influences the drift potential.
34 Spray Characteristics are Important to Understand Demonstrates Turbo Flat vs TurboDrop-5 MPH Wind
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