2

Recent History 

EFED last reviewed (11/12/2009, DP Barcode D346169) the environmental issues regarding spray 

drift in a response to public comments on proposed mitigation measures from the sulfometuron 

methyl Reregistration Eligibility Decision (RED).1

Summary of Registrant Conclusions and Proposal 

Our review has in view the Rights of Way (ROW) applications for which the registrant and 

stakeholders have previously requested better representation of current prevailing 

practices with regards to spray drift mitigation label language, including buffers to minimize 

off-site environmental risk. This review is intended to primarily address issues with regards 

to ROW applications although the low drift technologies discussed below are generally 

applicable to other product uses. The single “swath” adjustments discussed below, 

however, generally only apply to ROW uses (and even these uses cannot uniformly be 

assured to be single swath either2. The single / reduced swath number adjustment may be 

applicable to other specialized applications (such as spot treatments with hand-held 

equipment). EFED modeling to test the effect of these factors on drift is documented in the 

Appendix to this review. 

(1.) Registrant conclusions: 

Modeling with AgDRIFT® to simulate a single swath application shows that deposition, 

and consequently risk quotients, will be reduced by 50% relative to multiple swath 

applications. 

EPA Response: 

We generally concur with this conclusion. Single pass / swath applications can be 

simulated with AgDRIFT 2.01 and we were able to reproduce the registrant’s single swath 

results for Tier 2 AgDRIFT aerial applications (including those with ultra coarse drift 

profiles within AgDRIFT – see our Table 3 and also Tables 2, 3, and 4 in MRID 482619-01) 

and Tier 1 ground applications (see our Tables 1 and 3 and registrant’s Table 5 and 6). 

This has implications for rights of way uses of sulfometuron which are applied to areas 

which are likely covered in less than twenty swaths (a default assumption for both aerial 

and ground application analysis in AgDRIFT). Some re-evaluation of the previous buffer 

zones may be appropriate given many applications (forestry uses excluded) of 

sulfometuron methyl likely involve substantially less than twenty swaths. Although single 

 

a

1

 Relevant documents can be accessed through: http://www.epa.gov/opp00001/reregistration/sulfometuron_methyl/ or 

at: http://www.regulations.gov/search/Regs/home.html#docketDetail?R=EPA-HQ-OPP-2008-0129

The RED is specifically available at: http://www.epa.gov/opp00001/reregistration/REDs/sulfometuron_methyl_red.pdf

2

 Email dated 2/22/2011 from Jim A. Gray (Pesticide Feed and Fertilizer Director, North Dakota Dept. of Agriculture, 

Bismarck, ND) to Jim Roelofs, Govt. and International Services Br., Field and External Affairs Div., OPP). 
3

swath applications cannot be confirmed to be uniformly appropriate for even ROW 

applications, these types of applications likely will normally involve fewer than 5 swaths. 

With Tier 1 Ground Application assumptions in AgDRIFT, at 20 feet downwind from the 

treated area the predicted reduction drift from a five swath application versus a 10 or more 

swath application is minimal at all distances downwind from the treated area (Table 1). Use 

of a single swath (not practical for all rights of way applications) results in a 30% or more 

reduction in drift at distances of 20 or more feet downwind (Table 1). Similar reductions 

were obtained going from 20 to 1 swath (MRID 482519-01, Table 5). 

Table 1. Effect of a reduction in the number of swaths on drift from ground application (AgDRIFT 

Tier 1). 

Distance

downwind

1 vs. 10

Swaths

% Reduction

5 vs. 10

Swaths

% Reduction

1 swath %

Drift

5 swaths %

Drift

10 Swaths %

Drift

10 feet 13.64% 2.27% 3.80% 4.30% 4.40%

20 feet 30.00% 5.00% 1.40% 1.90% 2.00%

72 feet 60.00% 0.00% 0.20% 0.50% 0.50%

Using 50 percentile Tier 1 data and a 4.17 foot application height. Refer to MRID 482519-01, 

page 21 for more details. Derived from Table 6 in MRID 482519-01. 

 

(2.) Registrant conclusions: 

Further reductions in drift from aerial applications can be modeled for low drift technologies 

using nozzles producing extremely coarse and ultra coarse droplet distributions in high 

spray volume, low speed applications by helicopter. With the latter low drift conditions, offsite deposition is negligible, and buffers are not required to obtain a level of protection for 

non-target aquatic and terrestrial plants that is equivalent to EPA's target values (Keigwin, 

2009). 

EFED Response: 

Clearly the new application technologies can reduce drift substantially although more data 

and/or model development and validation are needed to fully confirm the effectiveness of 

these new technologies in actual practice. The EFED reviewed some of the secondary 

options available in AgDRIFT 2.01 Tier 2 aerial application mode which include application 

equipment and method scenarios that reduce drift beyond those available in the standard 

Tier 2 options. Specifically, EFED evaluated the Accu-Flo 028 nozzle drift predictions3

 

3

 The model predictions discussed here are from specific Spray Drift Taskforce (SDTF) experiments which 

were used in the development of the empirical model AgDRIFT; these datasets are made available in AgDRIFT for the 

estimation of drift under specific application scenarios. Note that while these data are vetted and accepted for support of 

EFED’s spray drift models, this does not necessarily translate into a specific dataset with a specific nozzle type as being 

representative of current technology in use for a specific pesticide / use site combination. 
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with AgDRIFT 2.01 and obtained nearly identical results to those presented in the 

registrant’s submission (which used the same input parameters for AgDRIFT 2.0.09). We 

also tested the Accu-Flo 047 dataset in AgDRIFT (also delivering ultra coarse droplet size 

spectra when applied at a speed of 40 mph or 60 mph) and found similar drift reductions 

from the use of this equipment. 

(3.) Registrant Conclusions: 

The limitations in the AgDRIFT® ground model can be overcome by consideration of the 

underlying experimental data and by supplementing the SDTF data with results of the 

Canadian Drift Model. Data from the SDTF shows that the AgDRIFT® model 

overestimates drift from the extremely coarse nozzles used in turf and ROW applications. 

EFED Response: 

Unfortunately, we are not able to validate the Canadian data and models for direct use to 

estimate exposure from uses in the USA at this time. In the registrant’s submission, the 

Canadian drift model is in particular a primary source of drift estimations for the low drift 

technologies in ground applications. OPP / EFED needs further validation of the level of 

drift reduction obtainable with these technologies in ground application. While we consider 

the Canadian data submitted by the registrant suggestive of the level of mitigation that 

might be achievable with the newer drift reduction technologies, we cannot yet rely on this 

data because it has not been validated for use within OPP. However, as also discussed in 

the registrant’s submission, with the underlying data used for AgDRIFT ground spray drift 

predictions there is some limited verification of the level of drift reduction obtainable with 

technology delivering extremely course to ultra course droplet spectra (utilizing “8010LP” 

nozzles). The 8010LP data are not currently accessible through AgDRIFT4 but are 

available in a report submitted to EPA (MRID 43508001, SDTF Study I94-001). Drift 

reduction relative to comparable Tier 1 AgDRIFT runs was about 32 to 86% at 25 to 75 

feet from the treated area (Table 2). 

Table 2. Comparison of standard Tier 1 ground application predicted drift with drift from nozzles 

delivering extremely course droplet spectra. 

(Boom Height = 1.67 feet) (Boom Height = 4.17 feet)

Drift

Measured

at:

% 

reduction 

w/ 8010LP 

Tier 1  

% drift  

8010LP %

drift  

% 

reduction 

w/ 8010LP

Tier 1  

% drift  

8010LP %

drift  

25 feet

downwind 84.31% 1.02% 0.16% 32.75% 1.71% 1.15%

75 feet

downwind 85.71% 0.35% 0.05% 45.61% 0.57% 0.31%

Comparison of the SDTF data with the 8010 LP nozzle (VMD = 762 um) with the AgDRIFT Tier 1 scenario

(VMD = 341 um) for both low and high boom applications. 90th Percentile curves all at 4 swaths (See MRID,

48251901, p. 22, Table 7).

 

4

 The AgDRIFT user interface for ground applications currently only includes the Tier 1 module with very limited user 

options; if and when a Tier 2 option for 
5

(4.) Registrant Conclusions: 

Considering the difference between the model and the experimental data, the buffer 

distance can be reduced to 5 ft for low boom (hand held) sprayers and 10ft for high boom 

ground sprayers to obtain RQs equivalent to those calculated for the multiple swath 

application and fine to medium/coarse DSD used as the basis for EPA's buffer proposal. 

The Canadian drift model demonstrates that applications with low boom, extremely coarse 

nozzles will produce lower off-target deposition than predicted by the AgDRIFT® model. 

The same level of protection targeted by EPA at 30 ft for spot applications with hand-held 

sprayer applications can be obtained at 3 ft using deposition from the experimental trials or 

with the Canadian model for extremely coarse nozzles. For high boom applications with 

coarse or very coarse nozzles, the Canadian model predicts deposition similar to the EPA 

target values at 10-15 ft. 

EFED Response: 

As noted above, we are unable to verify the representativeness of the Canadian drift 

model for use in US pesticide regulation. Other evidence from data used to develop 

approved EFED models does show that some significant reductions are available with 

equipment set to deliver courser spray spectra and with a reduced number of swaths. 

The analysis of specific data sets (as discussed above in this review) does show that there 

is potential for significant reductions in spray drift with the use of nozzles and application 

methods that deliver extremely course or ultra course droplet spectra. Based on the 

AgDRIFT modeling scenarios presented below in Table 1, Table 2, and Table 3, we cannot 

confirm the registrant’s conclusion that 5 ft and 10 ft buffers for ground applications of 

sulfometuron would be adequately protective of non-target plant species. These data do 

show that if applications are made delivering extremely course droplet spectra a modest 

reduction in buffers could be made while also obtaining exposure reductions. As an 

example, at a boom height of 1.67 spray drift from ground applications could be reduced 

from 0.35 to 0.16 % while reducing a buffer from 75 to 25 feet (Table 2). EFED is not in a 

position to determine, however, whether such equipment is being routinely used to the 

exclusion of equipment delivering finer droplets and under environmental allowing more 

drift to occur. 

ANALYSIS 

A selected summary of our analysis to validate the registrant’s submission (using options 

available in AgDRIFT is provided in Table 3, additional modeling documentation is 

provided in the Appendix to this review. Note that additional analysis was previously 

provided in DP Barcode D346169 (“Response to Environmental Fate and Effects related 

Comments on Sulfometuron Reregistration Eligibility Document”, dated 11/12/2009). 

We were unable to validate at this time the Canadian model based analysis by the 

registrant (MRID 4826519-01, Tables 7, 8, 9, and 11 and Figures 1 to 3). Nonetheless, the 
6

data validated for AgDRIFT suggests that there can be (for example) a 90% reduction in 

drift from aerial applications at 50 feet with use of selected equipment. (Compare Run ID 2 

with Run 11a/11b in Table 3.) 

The amount of drift from the best nozzles for aerial applications is even lower than the drift 

estimated with single swath ground applications (representing some Rights of Way 

applications) using currently available Tier 1 options in AgDRIFT (Run ID D6-1 and D6-3)5

. 

For drift from ground applications at about 25 to 75 feet, approximately 30 to 90% 

reductions (compared to application methods and conditions normally assumed in 

AgDRIFT Tier 1) may be possible with fewer swaths (4 is a reasonable maximum expected 

number for most uses) and use of equipment applied to deliver extremely course droplet 

spectra. The amount of reduction is highly dependent on boom height with the best 

percentage reductions obtained with a lower boom height (Table 2). 

Table 3. Comparison of previous aerial modeling to some of the best drift reduction options 

currently available in AgDRIFT for aerial or ground applications. 

DISTANCE 

DOWN WIND 

(FEET) 

MODE: 

AERIAL 

TIER II 

MODE: 

AERIAL 

TIER II 

MODE: 

AERIAL 

TIER II 

MODE: 

GROUND 

TIER I 

MODE: GROUND 

TIER I 

Lbs ai/A 

[% of rate]

Lbs ai/A 

[% of rate]

Lbs ai/A 

[% of rate]

Lbs ai/A 

[% of rate]

Lbs ai/A 

[% of rate]

0 0.0769 

[27.34] 

0.1124 

[40.0] 

0.1124 

[40.0] 

0.2834 

[100.8] 

0.2810 

[100.0] 

7 NC 0.0127 

[4.52] 

0.0134 

[4.78] 

0.0180 

[6.40] 

0.0200 or 

 0.0170 (EPA) 

[7.10] 

13 NC 0.0026 

[0.94] 

0.0024 

[0.87] 

0.009 

[3.20] 

0.0071 or 

0.0073 (EPA) 

[2.50] 

15 NC NC NC NC 0.0060 

[2.2]

20 NC 0.0008 

[.0.27] 

0.0008 

[0.275] 

0.0057 

[2.00] 

0.0040 

[1.40] 

26 NC 0.0004 

[0.16] 

0.0004 

[0.15] 

0.0042 

[1.50]

0.0027 

[0.90] 

50 or 52 0.019 

[6.77] 

0.0002 

[0.09] 

0.0002 

[0.08] 

0.0010 

[0.30] 

0.0020 

[0.70] 

72 or 75 0.0127 

[4.52] 

0.0002 

[0.09] 

0.0003 

[0.10] 

0.0015 

[0.50]

0.0006 

[0.20]

100 0.0091 

[3.23] NC NC NC NC 

125 NC 0.0000 

[0.0001] 

0.0000 

[0.0001] NC NC 

200 0.0039 

[1.39] 0 0 NC NC 

500 0.0016 

[0.59] 0 0 NC NC 

 

5

 Note, however, that if coarser nozzle data could be selected for ground applications then the drift estimates would be 

lower as represented in Table 2. 
7

750 0.0012 

[0.44] 0 0 NC NC 

900 0.0011 

[0.39] 0 0 NC NC 

Run ID1 2 11a (EPA) 11b 

(DuPont) 

D6-3 

(DuPont) 

D6-1 

(DuPont) 

Key Input Assumptions 1

Applic. Rate, lb 

ai / A 0.281 0.281 0.281 0.281 0.281 

Wind Speed, 

mph 10 10 10 10? 3

 10? 3

Application 

height, ft. 10 10 10 4.17 2

 4.17 2

Nozzle set info NA Accuflo 028 Accuflo 028 NA NA 

Median Droplet 

Size (um) 384 1213 1213 341 341 

Drop size 

distribution 

Coarse 

(ASAE) 

Very to 

extremely 

coarse 

(ASAE) - 

Now Ultra 

Coarse 

Very to 

extremely 

coarse 

(ASAE) - 

Now Ultra 

Coarse 

Fine to 

medium coarse 

(ASAE) 

Fine to medium 

coarse (ASAE) 

# of Flight lines 

(Swaths) 20 1 1 10 1 

Data Percentile NA NA NA 50 50 

Spray Volume, 

gal/ A 10 10 10 NA NA 

Application 

Equipment 

WASP 

Helicopter 

WASP 

Helicopter 

WASP 

Helicopter Ground Ground 

1

 Run #2 is repeated from the previous REVIEW by EFED; Runs 11a and 11b represent the 

registrant’s choice (see MRID 48261901) of an aerial application equipment / method option in 

AgDRIFT said to represent the better types of application methods currently in use. Note that these 

are single swath scenarios and therefore the results only apply to single pass rights of way 

applications. Runs D6-3 and D6-1 represent the best options to minimize drift from ground 

applications that are currently available in AgDRIFT (including examination of the impact of 

reducing the number of swaths to better represent most rights of way applications.) 

2

 Select the “high boom” option for AgDRIFT ground application model input. 

3

 Believed to be on average about 10 mph, but this is not specified in the AgDRIFT model documentation. The 

Tier 1 data likely reflect data collected at a wind speed of about 10 mph as this is generally the default 

assumption used by AgDRIFT.

 
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APPENDIX 

Sample Input and Output Data: AgDRIFT Accuflo 028 Nozzles, Rights of Way application 

Figure 1. Input and Drift at 50 feet for Accuflo 028 ROW application (50 ft). 

Figure 2. . 

Input and Drift at 50 feet for Accuflo 028 ROW application (15 ft). 
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Figure 3. Droplet distribution input for AgDRIFT: Accu-Flo 028 nozzles. 

 
10

Figure 4. Accu-Flo 028 nozzle specifications. 
11

Figure 5. Input screen and sample output for Accu-flo 047 nozzle, 40 mph application (for comparison to the 

Accu-flo 028 run). 

Figure 6. Droplet size spectrum for SDTF Accuflo 028 equipment. 

*************************************** 
12

Figure 7. AgDRIFT input and sample output screen: Ground application, Tier 1, high boom, single swath 

(comparable to the right side of Table 5 in registrant submissions (MRID 482519-01). 
13
14

Figure 8. AgDRIFT Tier 1 Ground Application single swath (compare with MRID 48251901, Table 6 – column 

1).