Accurate Modeling for Drift Reduction:
General Overview and Regulatory
Status
April 11th, 2014
Dan Dyer
On Behalf of the CLA Spray Drift Issue Management Team
Spray Drift Regulation
• Spray drift is complex…




Ground, aerial, orchard/airblast sprays
Broad range of technologies of spray equipment
Significant differences in geography/climate
Conservative drift models (perceived drift issue)
• But can be well managed…
 Local applicators/growers understand appropriate
conditions for application and minimizing drift
 Training / certification / education
 Pesticide Label Restrictions – wind speed, buffers,
etc.
 Newer drift reducing technologies
Spray Drift Regulation
• Recently released spray drift guidance for use
of AgDRIFT in human and ecological
exposure/risk assessment
 EPA-HQ-OPP-2013-0676 “Consideration of Spray
Drift in Pesticide Risk Assessment”
• CLA supports development of appropriate drift
assessment methodologies
• However, EPA guidance is too restrictive and is
limited in ability to make higher tier refinements
Factors Influencing Spray Drift
• Spray Characteristics
 Droplet size
 Chemical / Formulation / Adjuvants
• Equipment & Application
 Nozzle type, size, orientation
 Nozzle pressure
 Height of release
• Weather, etc.
 Air movement (direction and velocity)
 Temperature & humidity
 Air stability/inversions
Droplet Categorization - ASABE
Approximate
Category
Symbol
Color Code
Dv0.5 (VMD)
(microns)
Extremely Fine
XF
Purple
≈50
Very Fine
VF
Red
<136
Fine
F
Orange
136-177
Medium
M
Yellow
177-218
Coarse
C
Blue
218-349
Very Coarse
VC
Green
349-428
Extremely
Coarse
XC
White
428-622
Ultra Coarse
UC
Black
>622
From: ASABE Standard S-572.1
Need to select
droplet size to
maximize efficacy
and minimize drift
AgDRIFT to Calculate Buffers
• EPA 2014 guidance uses AgDRIFT to determine
drift for terrestrial (plant/animal) and aquatic habitat
• AgDRIFT based on Spray Drift Task-force data
 48 unique SDTF Deposition Datasets
 Excellent quality & GLP
 Used older (1992-93) spray application technology
• Several conservative approaches result in
unrealistic ground drift estimates
• Unable to refine drift estimation using drift
reducing technologies (DRT) and best
management practices
AgDRIFT – Overestimation of Drift
• AgDRIFT produces unreasonably conservative drift
estimates when compared to existing drift data sets
Comparison Between AgDrift Outputs vs. Field Data
AgDrift Assumes 20 Spray Swaths, 90th% tile
1.0
% of Applied
0.8
0.6
SDTF 1992
SDTF 1993
Wolf (PMRA)
Ganzelemier
AgDrift (20 swaths)
0.4
0.2
0.0
0
200
400
600
Distance (ft)
800
1000
Figure Courtesy J. Wright
AgDRIFT – Scale-up Overestimation
• SDTF Data is
foundation for
AgDRIFT, but use of
multipliers to scale-up
to a ‘typical’ field is
much too conservative
• 90th %ile curves
inappropriate
• Gross overestimate at
far-field distance
Figure Courtesy J. Wright
2011 AAFC Data – Multiple Swaths
• Dr. Tom Wolf of Agriculture and Agri-Food Canada
(AAFC) developed drift dataset as basis for PMRA
buffer zone calculator
Deposit (% of applied)
10
•
1
1
1
No significant deposition
after 4-5 swaths (~250-300 ft)
1
1
2
0.1
1
5
5
2
3
4
0.01
3
4
8
9
6
7
10
8
9
7
6
10
1
2
5
3
4
8
6
10
9
7
5
1
2
3
4
10
8
6
9
7
5
10
1
2
3
4
8
7
9
6
0.001
1
2
5
10
20
40
Downwind distance (m)
120
AgDRIFT – Overestimation of Drift
Nozzle Trial “Data Lumping”
Approximate
Category
Symbol
Color Code
Dv0.5 (VMD)
(microns)
Extremely Fine
XF
Purple
≈50
Very Fine
VF
Red
<136
• In AgDRIFT, SDTF data was
consolidated into two
categories:
Very Fine to Fine
Fine
F
Orange
136-177
Medium
M
Yellow
177-218
Coarse
C
Blue
218-349
Very Coarse
VC
Green
349-428
Extremely
Coarse
XC
White
428-622
Ultra Coarse
UC
Black
>622
Fine to Medium/Coarse
• Inappropriate to evaluate
medium or coarser sprays
• Inadequate for current nozzle
technology
Nozzle Types
Flat Fan Nozzles
Air Induction Nozzles
11
AgDRIFT
Wind Speed “Data Lumping”
• Drift at distance, is influenced by data generated in high
wind (25% of SDTF ground data with >20 mph wind!!)
• 90th percentile could be ‘off-label’
AI11004
1
0.1
0.01
90th Pct
1
50th Pct
Mean
0.1
0.01
1E-3
1E-3
1
10
log - Down Field Distance (m)
12
10
Percent of Applied
Wind (mph)
8.4
8.8
11.6
12.8
20.5
10
Percent of Applied (log)
Nozzle - 11004
100
1
10
Down Field Distance (m) - log
Dr. T. Wolf AAFC '2000
100
AgDRIFT – Overestimation of Drift
• Summary
• Mathematical model used in AgDRIFT to
describe the conservative 90th percentile drift
curves are subjective, and overestimate drift
• ‘Best fit’ curves in AgDRIFT never
intersect zero
• Lumping of data for trials with different nozzles
(spray quality / droplet sizes), and wind speed
produces excessive overestimates* of drift
from ground sprays, and removes capability to
refine model
* in some circumstances AgDRIFT can predict
movement of more off-target material than the
amount applied
Drift Overestimation – The Impact?
• AgDRIFT used to calculate proximity distances
and buffers for FIFRA ecological and human
health risk assessments, and Endangered
Species Risk Assessments
• Appropriate for ‘screening’ assessment, but
requires refinement options
• Risk should be refined before buffer size is
determined (mitigation)
Large Action Areas
(Endangered Species)
• Spray Drift – 360
degrees, wind
blowing in all
directions,
simultaneously
• Threshold’ = EEC /
LOC
• EEC from AgDrift
Significant overestimate of
action area and potential
buffer distances
Drift Overestimation –
Impact on Agriculture
• Impact on agriculture (example)
• ~600 feet of field or parts of field
cannot be treated
Drift Overestimation –
Impact on Agriculture
• ‘Freedom to operate’ for grower
 Possible need to remove land from production as more
buffers and larger buffers are required (value / cost?)
 Cost effectiveness of having to use ground applications
instead of aerial
• Resistance Development
 Cutting rates to meet buffer requirements
 No applications to certain parts of field
 Incomplete coverage due to coarser spray droplet
Spray Drift – A Pragmatic Solution
• Need to find appropriate balance between
efficacy, drift and resistance management, to
allow cost-effective pest control.
 Model refinement is necessary – reasonable
conservatism
 ‘Drift education’ / Best Management Practices are critical
 Automation is desirable to allow flexibility
REGDISP
• Model built on AGDISP (v. 8.26)
• USFS made code available to Industry
• the current EPA accepted version of AGDISP
• desire to keep the mechanistic ground model
• No changes to existing AGDISP code existing
• Better interface for AGDISP calculators
• Enables parsing of data/ addition of data
• Addresses issues with AgDRIFT described
19
Canada Drift Regulation
• Pest Management
Regulatory Agency in
Canada worked with Dr.
Tom Wolf of Agriculture
and Agri-Food Canada
(AAFC) and developed
their own dataset as basis
for their buffer zone
calculator
• Launched in 2011
REGDISP Data Sets
•
•
•
•
Agricultural Agri Food Canada (AAFC) ‘2000
Agricultural Agri Food Canada (AAFC) ‘2004
Agricultural Agri Food Canada (AAFC) ‘2011
49 unique AAFC Deposition Datasets
• Spray Drift Task Force ‘1992
• Spray Drift Task Force ‘1993
• 48 unique SDTF Deposition Datasets
• 97 unique deposition datasets
21
Canadian Field Study Design (‘00 and ‘04)
XR8001, XR8003, AI110025,
AI11005, AI11004 Nozzles
Fine to V. Coarse sprays
60 and 90 cm boom heights
Wind speed = 3 to 12 m/s
Single pass, 18m (60 ft) spray
boom
Data Fit Method
Log/Log Transform Data
Since Deposition Data is highly non-linear
1. Log Transform
2. Simple Regression (y=mx+b)
0.006
Fraction of Applied
0.005
0.004
0.003
0.002
0.000
0
20
40
60
80
100
120
Distance (m)
Fraction of Applied
0.001
1E-3
• Accurate description of data
• Doesn’t assume drift is unlimited
1E-4
23
10
100
Distance (m)
Deposition Data Calculation Tab
1.
2.
3.
4.
5.
6.
24
Select Dataset
Select Nozzle
Boom Height
Wind Speed
Enter Rate
Run
Use Existing Calculators (and Code)
Toolbox
25
Consideration of DRTs in Risk
Assessment
• DRTs are proposed for use in reducing the size
of required buffers
 Promote Best Management Practices (BMPs)
• Recommendations for specific Spray Quality or
Droplet Size likely needed to ameliorate ESA
restrictions – and maintain a viable product
• REGDISP facilitates consideration of specific
field data or combinations of DRTs in
determining a suitable action area or buffer
distance
Pragmatic Approach to Spray Drift
• Use of REGDISP as conservative, yet realistic
drift model
 No ‘infinite’ drift
 Ability to refine ground spray drift estimates –
spray quality, wind, DRTs, BMPs, etc.
 Defines reasonable proximity/buffer distances to
expedite FIFRA and endangered species risk
assessments
• Education / Stewardship
 Promote Best Management Practices
 CropLife, chemical producers, nozzle manufacturers,
product distributors, retailers, etc.
 Ag extension, federal/state agencies, universities
 Continued research
Pragmatic Approach to Spray Drift
• Use of automation of spray technology
 e.g. GIS on conjunction with automated nozzle
switching allows precision application with respect to
buffer areas
• Need to provide spray drift options that growers
and applicators can use today to:
• allow safe use of products (human and
ecological),
• without unduly impacting growers’ ability to
effectively produce crops
Thank you