Understanding Spray Drift. Robert E. Wolf Extension Specialist Application Technology. Biological and Agricultural Engineering. Why Interest in Drift?. Spotty pest control Wasted chemicals Off-target damage More high value specialty crops Urban sprawl and..... Less tolerant neighbors
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Robert E. Wolf
Extension Specialist Application Technology
Biological and Agricultural Engineering
concerns! (Negative) (Perceptions)
Movement of spray particlesand vaporsoff-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
Vapor Drift - associated with volatilization (gas, fumes)
Particle Drift - movement of spray particles during or after the spray application
unpredictable and variable in direction.
Height Above Crop Canopy, Feet
5 mphWind Speeds Gradients
The relation between height above the canopy of a crop like cotton or soybean and the speed of wind.
5 0 5 10 15Wind Patterns Near Shelterbelts
Distance from shelterbelt (tree heights)
Generalized pattern of wind in the neighborhood of a shelterbelt.
Adapted from Survey of Climatology:
Griffiths and Driscoll,
Texas A&M University, 1982
Diagram of wind around a building.
Adapted from Farm Structures*
* H.J. Barre and L.L. Sammet, Farm Structures (Wiley, 1959)
Wind speed - knots, feet/min, meters/sec, mph
Maximum, average, current wind speed
- knots, feet/min, meters/sec, mph
Maximum, average, current wind speed, temp, wind chill- knots, feet/min, meters/sec, mph
All wind speed features plus temp, wind chill, dew point, heat index, relative humidity
Plastimo Iris 50**
Wind Meters and Compass
*Prices for Wind Meters taken from Gempler’s 2002 Master Catalog
**Plastimo Airguide Inc., 1110 Lake Cook Road, Buffalo Grove, IL 60089(708-215-7888)
Under normal conditions air tends to rise and mix with the air above. Droplets will disperse and will usually not cause problems.
Increasing TemperatureTemperature Inversions
Under these conditions
the temperature increases as you move upward. This prevents air from mixing with the air above it. This causes small suspended droplets to form a concentrated cloud which can move in unpredictable directions.
generator is recommended to
identify inversion conditions.
Volume Median Diameter (VMD)
% Volume in droplets less than
200 microns in size
One micron (m) =1/25,000 inch
pencil lead 2000 (m)
paper clip 850 (m)
staple 420 (m)
toothbrush bristle 300 (m)
sewing thread 150 (m)
human hair 100 (m)Comparison of Micron Sizes for Various Items: (approximate values)
1/2 of spray volume = smaller droplets
1/2 of spray volume = larger droplets
High Relative Humidity
Low Relative Humidity
Demonstrates Turbo Flat vs TurboDrop-5 MPH Wind
*USDA ARS College Station, TX
Border EG 250
Border XTRA 8L
Double DownParticipants in the Study:
Allow enough time for:
Try not to 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.
Minimizing spray drift is in the best interests of everyone. Do your part to keep applications on target.
Thank You Application