Spray Drift and its Mitigation

John Unsworth
8th April 2010

When forced under pressure through sprayer nozzles liquids emerge as thin elongated sheets with edge instabilities that break up into small aerosols or particles having nearly a thousand fold range in spherical diameters. Owing to gravitational forces and the viscosity of air, the rate of fall to ground can be predicted by Stokes Law and is proportional to the radius of the particles. The rate of fall before a particle hits the ground (or conversely how long a particle remains in air before it falls a given distance) is modified by entrainment in a mobile air mass. Rate of fall of a spray particle will also be influenced by the rate of evaporation of the liquid constituting the aerosol. The longer the aerosol remains in air before falling to ground (or alternatively striking an object above ground) the greater the opportunity to be carried away from its intended target (e.g., crop canopy). In general, all size classes of spray particles are capable of movement off-target, but the smallest particles would move the farthest before depositing on the ground. Drift has been historically considered to be the movement of pesticide residues via air masses during and after application. Post application movement of pesticide residues (i.e., after deposition on plants or soil) via volatilization can be classified as secondary or indirect drift. A comprehensive review of spray drift and its mitigation was published in 2005 (Felsot 2005)1 and is currently the subject of an IUPAC funded project2. A publication based on this project should be available in 2010.


Although drift has a negative connotation because of its usual association with off-target (or out of field) impacts, spray drift within, for example, the canopy during application can increase the potentially bioavailable material on foliage. On the other hand, off-target or out-of-field drift during application may produce a high concentration of residues that potentially have an immediate or acute effect on nontarget organisms.

Highly concentrated agrochemical residues generated during spray application can move (drift) beyond target foliage (or soil when a pre-emergent herbicide or fumigant is used) to nontarget receptors including water, plants and animals. Nontarget receptors may be acutely exposed and therefore face the greatest risk of adverse effects during and immediately after spray application. In addition to movement of agrochemical residues in turbulent air masses downwind of application, residues can also become concentrated in inversions or stable air masses and be transported long distances. Similarly, agrochemicals can volatilize from plant and soil surfaces in comparatively high concentrations for several days after application. These secondary drift residues also pose a hazard to nearby nontarget receptors. Factors affecting spray drift include droplet size, which can be modified by the nozzle type, nozzle spray angle and nozzle spacing, certain formulation adjuvants, wind direction, wind speed, air stability, relative humidity, temperature and height of released spray relative to the crop canopy3,4.

In the US the assessment of spray drift has been studied in detail by the Spray Drift Task Force which was set up in 19905 by 38 agricultural chemical companies to generate data to fulfil US Environmental Protection Agency (EPA) spray drift data requirements. This Task Force has developed an evaluation tool to estimate the environmental exposure from spray drift at time of application6. In Europe drift is incorporated into the FOCUS model which predicts the concentration of pesticides in surface water due to run-off, erosion and drift7.

The US Spray Drift Task Force has issued several publications dealing with aerial application12, ground hydraulic application13, airblast application in orchards14 and chemigation15 and their relationship to spray drift. In Germany the Ganzelmeier Tables have been developed using different types of sprayers and nozzles so that applicators can choose equipment that will minimise drift16,17. In the UK a government website is available which allows applicators to examine the drift reduction ratings of many types of equipment18. In the EU there is a move to introduce a “Standardised Procedure for the Inspection of Sprayers in Europe” –SPISE19 


  1. A.S. Felsot, Evaluation and Mitigation of Spray Drift, Proc. International Workshop on Crop Protection Chemistry in Latin America; Harmonized Approaches for Environmental Assessment and Regulation, 14-17 February, 2005, San Jose, Costa Rica
  2. International Union of Pure and Applied Chemistry, Agrochemical Spray Drift: Assessment and Mitigation, Project 2001-023-1-600
  3. A.G. Dexter, Herbicide Spray Drift, A-657 (Revised), North Dakota State University and the University of Minnesota, August 1993
  4. R.N. Klein, L. Schulze and C.L. Ogg, Spray Drift of Pesticides, NebGuide G1733,University of Nebraska-Lincoln Extension, September 2007
  5. US Environmental Protection Agency, Pesticide Registration (PR) Notice 90-3: Announcing the Formation of an Industry-Wide Spray Drift Task Force, April 6, 1990
  6. US Spray Drift task force, AgDRIFT® 2.0, January 2002http://www.agdrift.com/AgDRIFt2/DownloadAgDrift2_0.htm
  7. FOrum for Co-ordination of Pesticide Fate Models and their Use (FOCUS), Overview of FOCUS Surface Water
  8. US Spray Drift Task Force, A Summary of Tank Mix and Nozzle Effects on Droplet Size, 2001
  9. Reducing Spray Drift, Bulletin 816-00,  The Ohio State University, 2000
  10. J.C. van de Zande, J.M.G.P. Michielsen, H. Stallinga, M. Wenneker & B. Heijne, Hedgerow Filtration and Barrier Vegetation, International Conference on Pesticide Application for Drift Management, Waikoloa, Hawaii, October 2004
  11. A.J. Hewitt, Drift Filtration By Natural and Artificial Collectors: A Literature Review, Stewart Agricultural Research Services, Inc., October, 2001
  12. US Spray Drift Task Force, A Summary of Aerial Application Studies, 1997
  13. US Spray Drift Task Force, A Summary of Ground Application Studies, 1997
  14. US Spray Drift Task Force, A Summary of Airblast Application Studies, 1997
  15. US Spray Drift Task Force, A Summary of Chemigation Application Studies, 1997
  16. D. Rautmann, Drift reducing Sprayers - Testing and Listing in Germany. ASAE Annual International Meeting 27-30 July, 2003, Las Vegas, Nevada, USA.
  17. H. Ganzelmeier,  The Prospect Of European Harmonisation - Plant Protection Equipment Under Test,  Journal of Central European Agriculture (2002) 3 (4) 301-312
  18. UK Pesticides Safety Directorate, Officially Recognised LERAP Low Drift Rating Spray Equipment
  19. Standardised Procedure for the Inspection of Sprayers in Europe <SPISE>
Last modified April 8th 2010

Date added: 2010-05-10 01:44:51   
Last Updated 2010-06-29 09:29:20   
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