Page 1 of 4

Use of AgDRIFT and AGDISP in OPP Risk Assessments

Scientific Basis for the Models

EPA uses two peer-reviewed spray drift models (AgDRIFT and AGDISP) to estimate the 

contribution of spray drift to ecological and human health risk assessments. Both models

estimate drift fractions, as applicable to spray of liquid materials. In addition, AGDISP has 

limited capability to estimate drift fractions from dry materials application. 

The Spray Drift Task Force (SDTF), a coalition of pesticide registrants, was formed in 

1990, with the goal of developing a generic database of off-target drift information in support of 

spray drift data requirements for the registration of pesticides. In developing test protocols for 

laboratory and field studies, the SDTF consulted with technical experts from research institutions 

around the world and compiled a list of over 2,000 drift-related studies from the scientific 

literature. Between 1992 and 1995, the SDTF conducted a series of field and laboratory studies 

that provided the scientific basis for spray deposition and downwind drift predictions. These 

SDTF studies were designed and conducted in consultation with scientists at universities and 

research institutions, and were intended to provide a quantitative measure of the potential

environmental exposure of non-target organisms to a chemical of concern as well as for use in 

predicting human exposure from spray drift. More than 300 applications were made in 10 field 

studies to quantify spray drift from aerial, ground, and orchard airblast applications. After the 

field studies were completed, the results were peer reviewed at two public meetings of the 

Federal Insecticide Fungicide and Rodenticide Act (FIFRA) Scientific Advisory Panel (SAP). 

The report from the December 1997 meeting is available at 

http://www.epa.gov/scipoly/sap/meetings/1997/121097_mtg.htm and the report from the July
Page 2 of 4

1999 meeting is available at http://www.epa.gov/scipoly/sap/meetings/1999/072099_mtg.htm. 

Using the data from the SDTF field trials, the AgDRIFT model was developed to assess a 

variety of spray drift conditions. AgDRIFT, a modified version of the AGricultural DISPersal 

(AGDISP) model developed by the US Forest Service, was created under a Cooperative 

Research and Development Agreement between the EPA, the US Department of Agriculture’s

Forest Service, and the SDTF for estimating spray drift from aerial, ground, and orchard airblast 

applications. AGDISP is a “first-principles,” science-based aerial model1 which has been well 

established and can be used beyond the STDF test conditions. AGDISP/AgDRIFT algorithms 

have been formally validated using 161 SDTF field trial data for a wide range of aerial 

application and meteorological conditions2 

3

. 

Based on the SDTF data, AgDRIFT can predict Tier 1 (screening-level) drift fractions for 

aerial, ground, and orchard air blast applications. AgDRIFT can also predict drift fractions for 

higher-tiered modeling for aerial applications. Input features of the AGDISP and AgDRIFT

models provide the capability to alter over 30 parameters related to the aerial application method

including application technique, meteorology, spray material and atmospheric stability. 

AgDRIFT can also provide alternate, empirically based, predictions for ground and airblast 

sprayers which represent applications under different conditions. The AGDISP model also has 

application modules for ground spray and limited capability to model the spray of dry materials. 

In general, OPP uses the AgDRIFT model to assess spray drift from agricultural 

applications, whereas AGDISP is used for other types of pesticide applications, such as aerial 

application of mosquito adulticides. Both of these spray drift models are widely accepted in the 

 

1 Bilanin, A.J., Teske, M.E., Barry, J.W. and R.B. Ekblad. 1989. AGDISP: The Aircraft Spray Dispersion Model, 

Code Development and Experimental Validation. Transactions of the ASAE 32: 327-334.

2 Bird, S. L., S. G. Perry, S. L. Ray, and M. E. Teske. 2002. Evaluation of the AGDISP aerial spray algorithms in the 

AgDRIFT model. Environ. Toxicol. and Chem. 21(3): 672-681.

3 USEPA, 1997. Estimating Drinking Water Exposure as a Component of the Dietary Risk Assessment; Spray Drift 

Program, Washington, D.C. http://www.epa.gov/scipoly/sap/meetings/1997/121097
Page 3 of 4

scientific community for determining off-site spray drift and have been used by many US federal 

agencies and by pesticide regulatory authorities worldwide. 

Several updates have occurred in recent years to improve the performance and reliability

of AgDRIFT and AGDISP. When updates occur, OPP evaluates the latest versions of these 

models, and determines if changes are needed to OPP’s methodologies for estimating exposure 

and risk. For more information regarding these models, refer to: 

http://www.epa.gov/pesticides/science/models_db.htm.

Harmonized Model-Generated Spray Drift Fractions Usage in OPP Risk Assessments

The Agency has determined to use the AgDRIFT model generated spray drift fractions to 

assess spray drift exposure for pesticide applications. A harmonized understanding of the process 

for estimating spray drift fractions by both ecological and human health risk assessors will 

ensure consistency and provide more realistic risk estimates. Both of the draft guidances use 

harmonized AgDRIFT model scenarios for risk assessment purposes. In the absence of 

application parameters such as droplet size spectrum, release height, wind speed, and percent of 

swath displacement, as well as relevant meteorological conditions, on the product label, the 

following model input parameters for various application scenarios will be used to estimate spray

drift fractions:

 Ground Applications: high boom height, ASAE very fine to fine Drop Size 

Distribution (DSD), and a 90th percentile data without extended settings 

 Orchard/Airblast: Sparse (Young/Dormant) AgDRIFT

 Aerial Application: Tier I module. Additional parameters for aerial application 

include the following:

o ASAE Fine to Medium DSD, 

o a wind speed of 10 mph
Page 4 of 4

o 60 foot swath width, 

o release height of 10 feet,

o Boom Length of 76.3%, and

o Swath Displacement of 37%. 

Most of these parameters are recommended in the AgDRIFT model by the SDTF. The 

recommended droplet size spectra were also suggested in university extension material4for 

various pesticide types or uses and were consistent with SDTF recommendations.

Currently, this harmonized approach is being implemented for both ecological and human 

health risk assessments.

 

4 Wolf, R.E. and Bretthauer, S. 2009. Droplet Size Calibration: A new approach to effective Spraying. Kansas State 

University Agricultural Experimental Station and Cooperative Extension Service, Kansas State University, 

Manhattan, KS.