/

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHrNGTON, D.C. 20460

OFFICE OF PREVENTION,

PESTICIDES, AND TOXIC

SUBSTANCES

Chemical: Sulfometuron methyl

PC Code : 122001

DP Barcode: D346169

MEMORANDUM

DATE: November 12,2009

SUBJECT: Response to Environmental Fate and Effects related Comments on

Sulfometuron Reregistration Eligibility Document

FROM:

THRU:

TO:

Michael R. Barrett, Che~ist,,-:.-j ~~ <vcg

Keith G. Sappington, Biologist

C1!\Jl-..............,

Environmental Risk Branch 5

Environmental Fate and Effects Division (7507P)

Mah Shamim, Branch Chief

Environmental Risk Branch 5

Environmental Fate and Effects Divi IOn (7507P)

Russell Wasem, Chemical Review Manager

Tom Moriarty, Team Leader

Rick Management & Implementation Branch I

Pesticide Re-evaluation Division (7 508P)

1// / e/0 '7

Attached are the Environmental Fate and Effects Division's (EFED' s) response to

comments made by stakeholders on the Reregistration Eligibility Document for

Sulfometuron.! After compiling the comments related to proposed mitigation measures

I Available at: http://www.epa.gov/oppOOOO I/reregistrationlsulfometuron methyl!

The RED is specifically available at:

http ://www.epa.gov/oppOOOOI /reregistrationlREDs/sulfometuron methyl red.pdf

Stakeholder comments are available at:

http ://www.regulations.gov/searc hlRegsihome.html#docketDetail?R EPA· HQ PP-2008-0 129
2

including changes to the application rates, methods, and sites for sulfometuron methyl, 

EFED did follow-up modeling of sulfometuron methyl off-site drift which is a major 

source of exposure with the potential for unintended ecological effects. Results of the 

additional modeling, a summary list of environmental fate and effects related comments, 

and proposed specific responses to the stakeholder comments are given below. 

 
3

Part 1: Summary of New Spray Drift Analysis Using the 

AgDRIFT Model 

The stakeholder comments provided several suggestions for reducing the off-site impact 

of sulfometuron methyl applications and evaluating off-site transport via spray drift for 

more typical application scenarios. The commenters (including registrants, user groups, 

and other interested parties) provided information as well on the feasibility of specific use 

restrictions. The following AgDRIFT modeling results provide an evaluation of the 

impacts of these measures. 

Due to the fact that the Agency plans to prohibit fixed wing aircraft liquid spray 

applications (most, but not all, of the current sulfometuron methyl labels already only 

allow for use of fixed winged aircraft applications for solid formulations with fertilizers) 

this assessment focuses on rotary winged (helicopter) applications and drift from ground 

applications. Also, because a number of stakeholders indicated that lower application rate 

limits may be feasible and that improvements in application equipment may now further 

reduce drift, these factors were also investigated. Our analysis shows that substantial 

reductions in spray drift are possible with the implementation of these newer 

technologies. The specific modeling results are discussed in the following paragraphs. 

In Table 1 the results of modeling are presented for various aerial application scenarios 

with a rotary aircraft (WASP helicopter2) run with relatively conservative assumptions 

(such as a wind speed of 10 mph and a boom height of 10 feet). Here the main variable 

tested is the droplet size spectrum. The reductions in drift from lowering the application 

rate are essentially proportional to the rate applied. The use of equipment delivering 

coarser droplets can substantially reduce drift. For example, changing the droplet size 

spectrum from medium to very course reduces spray drift by 65.5% at 50 feet, 62.4% at 

100 feet, 70.0% at 200 feet, and 73.9% at 900 feet from the edge of the treated area (and 

if technologies are implemented which deliver very to extremely coarse droplet spectra 

along with rate reductions, even greater drift reductions are obtainable, see Table 2 and 

Table 3). Note that the AgDRIFT Tier II default scenario evaluated in the sulfometuron 

methyl RED assumes a fine to medium drop size distribution for aerial applications 

resulting in significantly more drift than each of the scenarios we tested in this 

assessment. 

Recognizing that in some types of uses a higher boom height may be needed (forestry 

and rights of way in rough terrain or with variable ground cover), we also compared the 

impact of spray delivered at a boom height of ten feet versus 15 feet for equipment 

delivering a very coarse spray spectrum (see Run IDs 3 and 4) – the higher boom height 

resulted in a increase in drift of 37.1% at 50 feet, 37.5% at 200 feet, and 50.0% at 900 

feet from the edge of the treated area (drift amounts were very low, probably rounding 

error with this value). Note that, even when field conditions would force a rotary winged 

craft application at a 15-foot boom, the far field drift with a very coarse droplet spectrum 

 

2

 The WASP helicopter is the only rotary winged aircraft represented in AgDRIFT. 
4

delivery is still somewhat lower (15-20%) than a coarse droplet spectrum delivery at a 

height of 10 feet (compare Run IDs 2 and 4). 

Table 1. Estimated amount of sulfometuron methyl spray drift from rotary aerial 

applications at various distances from a field treated with the proposed maximum 

labeled rate of 0.281 or 0.253 lb ai/A, different droplet size spectra, and other 

mitigation options. 

DISTANCE 

DOWN WIND 

(FEET) 

MODE: 

AERIAL 

TIER II 

MODE: 

AERIAL 

TIER II 

MODE: 

AERIAL 

TIER II 

MODE: 

AERIAL 

TIER II 

MODE: 

AERIAL 

TIER II 

MODE: 

AERIAL 

TIER II 

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]

Lbs ai/A 

[% of rate]

0 0.1116 

[39.70] 

0.0769 

[27.34] 

0.0558 

[19.85] 

0.0908 

[32.29] 

0.0502 

[19.83] 

0.0691 

[27.3] 

50 0.0336 

[11.93] 

0.019 

[6.77] 

0.0116 

[4.12] 

0.0159 

[5.67] 

0.0104 

[4.10] 

0.017 

[6.74] 

75 0.0218 

[7.76] 

0.0127 

[4.52] 

0.0082 

[2.9] 

0.0111 

[3.95] 

0.0073 

[2.88] 

0.0113 

[4.49] 

100 0.0161 

[5.71] 

0.0091 

[3.23] 

0.0058 

[2.05] 

0.008 

[2.83] 

0.0051 

[2.03] 

0.0081 

[3.20] 

200 0.008 

[2.84] 

0.0039 

[1.39] 

0.0024 

[0.85] 

0.0033 

[1.16] 

0.0021 

[0.84] 

0.0035 

[1.37] 

500 0.0034 

[1.21] 

0.0016 

[0.59] 

0.001 

[0.36] 

0.0013 

[0.48] 

0.0009 

[0.36] 

0.0015 

[0.57] 

750 0.0052 

[1.39] 

0.0012 

[0.44] 

0.0007 

[0.26] 

0.001 

[0.37] 

0.0006 

[0.25] 

0.0011 

[0.43] 

900 0.0023 

[0.84] 

0.0011 

[0.39] 

0.0006 

[0.23] 

0.0009 

[0.32] 

0.0006 

[0.22] 

0.0010 

[0.38] 

Run ID 1 2 3 4 5 6 

Key Input Assumptions 

Applic. Rate, lb 

ai / A 0.281 0.281 0.281 0.281 0.253 0.253 

Wind Speed, 

mph 10 10 10 10 10 10 

Application 

height, ft. 10 10 10 15 10 10 

Drop size 

distribution Medium Coarse Very coarse Very Coarse Very coarse Coarse 

Application 

Equipment 

WASP 

Helicopter 

WASP 

Helicopter 

WASP 

Helicopter 

WASP 

Helicopter 

WASP 

Helicopter 

WASP 

Helicopter 

(AgDRIFT Model Runs series 1) 

In Table 2 the impact of lowering the application rate is evaluated and the relative drift 

from ground applications are compared to the rotary aircraft application. These lower 

application rates have been tested upon the basis of suggestions by DuPont (please refer 

to the Docket for comments on the Sulfometuron Methyl RED for a copy of their 

proposal) and forestry interests. The aerial applications tested here are ones with 
5

equipment delivering a course droplet size spectrum representing a measure of 

improvement over the types of spray conditions originally modeled in the sulfometuron 

methyl RED. 

As before, lowering the application rate results in a nearly exactly proportional reduction 

in the amount of drift (Compare Run IDs 2, 7, and 8). Ground application results in 

much reduced drift compared with coarse sprays from helicopters: depending on whether 

a release height of 4.2 or 1.7 feet was chosen, the ground applications resulted in from 82 

to 89% less drift at 50 feet, 72 to 82% less drift at 200 feet, and 73 to 82% less drift at 

900 feet. 

Table 2. Estimated amount of sulfometuron methyl spray drift from rotary aerial 

and ground applications at various distances from a field treated with reduced 

application rates. 

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] 

0.0655 

[27.29] 

0.0543 

[27.27] 

0.2845 

[101.0] 

0.2831 

[101.0] 

50 0.019 

[6.77] 

0.0162 

[6.75] 

0.0133 

[6.70] 

0.0034 

[1.19] 

0.0021 

[0.74] 

75 0.0127 

[4.52] 

0.0107 

[4.47] 

0.0088 

[4.44] 

0.0025 

[0.87] 

0.0015 

[0.55] 

100 0.0091 

[3.23] 

0.0076 

[3.19] 

0.0063 

[3.14] 

0.0020 

[0.70] 

0.0012 

[0.44] 

200 0.0039 

[1.39] 

0.0033 

[1.36] 

0.0026 

[1.33] 

0.0011 

[0.40] 

0.0007 

[0.26] 

500 0.0016 

[0.59] 

0.0014 

[0.57] 

0.0011 

[0.5t] 

0.0005 

[0.17] 

0.0003 

[0.12] 

750 0.0012 

[0.44] 

0.0010 

[0.43] 

0.0008 

[0.42] 

0.0003 

[0.11] 

0.0002 

[0.08] 

900 0.0011 

[0.39] 

0.0009 

[0.38] 

0.0007 

[0.37] 

0.0003 

[0.08] 

0.0002 

[0.07] 

Run ID 2 7 8 9 10 

Key Input Assumptions 1

Applic. Rate, lb 

ai / A 0.281 0.240 0.199 0.281 0.281 

Wind Speed, 

mph 10 10 10 NS 4

 NS 4

Application 

height, ft. 10 10 10 4.17 2

 1.67 3 

Median Droplet 

Size (um) 384 384 384 341 341 

Drop size 

distribution 

Coarse 

(ASAE) 

Coarse 

(ASAE) 

Coarse 

(ASAE) 

Fine to 

medium coarse 

(ASAE) – 90th

%ile 

Fine to 

medium 

coarse 

(ASAE) - 

90th %ile 

Application 

Equipment 

WASP 

Helicopter 

WASP 

Helicopter 

WASP 

Helicopter Ground Ground 
6

1

 Run #2 is repeated from Table 1; Run #7 and 8 have identical inputs to Run #2 except for 

the lower application rates assumed. 

2

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

3

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

4

 NS = 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.

Finally, Table 3 presents scenarios which represent, based on information received in 

comments on the RED and additional follow-up communications with stakeholders, the 

best practical exposure reduction scenarios for sulfometuron methyl. Specifically, 

Table 3 presents the impact of using rotary aircraft and spray equipment capable of 

delivering very coarse to extremely coarse droplet size spectra at each of the proposed 

lower the application rates. Also presented is the relative drift from ground applications at 

the proposed reduced rate using more typical spray delivery efficiency (i.e., the 50th 

percentile drift data from the AgDRIFT empirical model). 

The modern technology coarser spray applications presented in Table 3 result in 

significantly reduced drift from older technology applications largely portrayed in Table 

1 and Table 2. For example, at the rate of 0.199 lb ai/A: compared to the “coarse” spray 

applications the “very coarse to extremely coarse” applications resulted in 50.5% less 

drift at 30 feet, 47.4% less drift at 50 feet, 45.5% less drift at 75 feet, 50.8% less drift at 

100 feet, 53.8% less drift at 150 feet, and 54.5% less drift at 900 feet downwind from the 

treated area. 

Table 3. Estimated amount of sulfometuron methyl spray drift from rotary aerial using 

equipment delivering very coarse droplet size spectra at various distances from a field 

treated with reduced application rates (also compared with ground applications). 

DISTANCE 

DOWN 

WIND 

(FEET) 

MODE: 

AERIAL 

TIER II 

MODE: 

AERIAL 

TIER II 

MODE: 

AERIAL 

TIER II 

MODE: 

AERIAL 

TIER II 

MODE: 

AERIAL 

TIER II 

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]

Lbs ai/A 

[% of 

rate]

0 0.0543 

[27.27] 

0.0394 

[19.81] 

0.0327 

[16.44] 

0.0558 

[19.85] 

0.0463 

[16.47] 

0.2835 

[101.0] 

30 0.0208 

[10.44] 

0.0131 

[6.59] 

0.0103 

[5.16] 

0.0186 

[6.63] 

0.0146 

[5.19] 

0.0038 

[1.37] 

50 0.0133 

[6.70] 

0.0081 

[4.08] 

0.007 

[3.52] 

0.0116 

[4.12] 

0.01 

[3.56] 

0.0023 

[0.83] 

75 0.0088 

[4.44] 

0.0057 

[2.84] 

0.0048 

[2.42] 

0.0081 

[2.90] 

0.0069 

[2.47] 

0.0016 

[0.57] 

100 0.0063 

[3.14] 

0.004 

[2.00] 

0.0031 

[1.56] 

0.0058 

[2.05] 

0.0045 

[1.60] 

0.0012 

[0.44] 

150 0.0039 

[1.95] 

0.0024 

[1.20] 

0.0018 

[0.90] 

0.0035 

[1.24] 

0.0026 

[0.93] 

0.0009 

[0.31] 

200 0.0026 

[1.33] 

0.0016 

[0.81] 

0.0012 

[0.60] 

0.0024 

[0.85] 

0.0018 

[0.63] 

0.0007 

[0.23] 

500 0.0011 

[0.55] 

0.0007 

[0.34] 

0.0005 

[0.25] 

0.0011 

[0.37] 

0.0007 

[0.26] 

0.0002 

[0.09] 
7

750 0.0008 

[0.42] 

0.0005 

[0.24] 

0.0003 

[0.17] 

0.0007 

[0.26] 

0.0005 

[0.18] 

0.0002 

[0.05] 

900 0.0007 

[0.37] 

0.0004 

[0.21] 

0.0003 

[0.15] 

0.0006 

[0.23] 

0.0005 

[0.16] 

0.0001 

[0.04] 

Run ID 8 11 12 13 14 15 

Key Input Assumptions

Applic. Rate, 

lb ai / A 0.199 0.199 0.199 0.281 0.281 0.281 

Wind Speed, 

mph 10 10 10 10 10 NS 1

Application 

height, ft. 10 10 10 10 10 4.17 

Median 

Droplet Size 

(um) 

384 476 519 476 519 341 

Drop size 

distribution 

Coarse 

(ASAE) 

Very 

Coarse 

(ASAE) 

Very 

Coarse to 

Extremely 

Coarse 

(ASAE) 

Very 

Coarse 

(ASAE) 

Very 

Coarse to 

Extremely 

Coarse 

(ASAE) 

Fine to 

medium 

coarse 

(ASAE) – 

50th %ile 

Application 

Equipment 

WASP 

Helicopter 

WASP 

Helicopter 

WASP 

Helicopter 

WASP 

Helicopter 

WASP 

Helicopter Ground 

1

 NS = 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. 
8

Part 2: Environmental Fate and Effects Related 

Stakeholder Comments and Agency Responses 

Stakeholder comments with specific comments / suggestions / recommendations are 

grouped into similar categories. A brief summary of the comment(s) is provided 

followed by the EFED response. 

Comment Group 1. 

SUMMARY OF COMMENTS: 

EPA received several comments regarding the term “under the forest canopy” noting that 

the phrase is vague and confusing. 

EFED Response # 1. 

The forest canopy is language suggested in the label review manual. SRRD has advised 

they will take back this language based on the label review guidance. The language here 

should follow the standards for other pesticides which are not registered for aquatic 

applications. 

******** 

Comment Group 2. 

SUMMARY OF COMMENTS: 

The Agency received comments that the current label language regarding “light sandy 

soil” does not provide useful application information. 

EFED Response # 2. 

This language is common among many sulfometuron methyl labels and is the design of 

the reregistration process that all labels will bear the same language. The objective of this 

language is to obtain consistency in weed control and reduce off-site transport in areas 

with erodible soil. The EFED does not believe it is feasible, from a technical or practical 

standpoint, to precisely define the problem soils exactly on the basis of soil textural 

composition and organic matter content. However, the EFED agrees that general 

language, like that provided by the commenter, might be helpful to applicators: 

Soils that are subject to wind erosion usually have high silt and / or very fine and 

fine sand textural fractions. Low organic matter also tends to increase a soil’s 

wind erosion potential 

******** 

Comment Group 3. 

SUMMARY OF COMMENTS: 

The Agency received comments stating that the term “aquatic plants” is too vague and 

does not provide useful application information. 

EFED Response # 3. 

The EFED believes that the term “aquatic vegetation” is reasonable and clear. If 
9

additional clarification is desired, however, the following text (bolded) may be added to 

the label for clarification: 

“Do not apply within 500 feet of bodies of water containing aquatic vegetation 

(e.g., submerged and emergent aquatic plants, algae), water used as an 

irrigation source and crops.”

Note that the buffer width may be further relaxed with the proposed rate reductions and 

the emphasis on use of application technology that further reduces spray drift. 

******** 

Comment Group 4. 

SUMMARY OF COMMENTS: 

The Agency received numerous comments regarding the “release height” modeled in the 

RED and required on the sulfometuron methyl. Commenters noted that in commercial 

forestry scenarios, a 10 foot release height is often unsafe. As an example, it was noted 

by one respondent that, in Washington state forestry application areas are “1) located in 

mountainous terrain and 2) have scattered wildlife trees (required by state forest practice 

rules) in them.” Several commenters noted support for language that provided for safety 

without mandating a 10 foot release height. 

EFED Response # 4. 

The Agency uses AgDRIFT, a peer reviewed predictive models that is primarily designed 

for commercial agricultural scenarios. In this context, a 10-foot release height is 

achievable and desirable for minimizing off-site transport. However, as pointed out in the 

numerous comments above forestry uses often are in scenarios where the ground cover 

and/or terrain make such a low release height impractical and unsafe. The use of a 10 or 

15 foot release height is the predominantly used range of the AgDRIFT model and has 

been used to facilitate comparisons by the Agency between application scenarios with 

different inputs such as application rate, or droplet size. 

The EFED recommends that the proposed language regarding the release height should 

be modified to insure that practical and safe methods will be used in forestry, rights of 

way, or other application situations where the terrain and land cover variation would 

make a set release height impractical. The labels should require that spray height be the 

minimum level that meets safety standards and drift prevention objectives. One example 

of how this might read is: 

Sulfometuron methyl should be applied at a boom height as close to 10 feet as is 

efficacious and safe (to minimize the zone of drift of potentially ecologically 

significant amounts of sulfometuron methyl). Under certain circumstances (e.g., 

in areas of rough terrain or variable land cover) it may be necessary to apply 

sulfometuron methyl at a greater boom height. State and local best management 

practice guidelines and directives should be consulted and followed. 
10

The final language chosen should be consistent with other labels for products with drift 

concerns. The impact of boom height, nozzle type (impact of using nozzles that deliver a 

coarser spray spectrum such as “rain drop” nozzles) and other factors on off-site drift 

levels has been discussed in the “Summary of New Spray Drift Analysis Using the 

AgDRIFT Model” section. 

******** 

Comment Group 5. 

SUMMARY OF COMMENTS: 

One commenter noted to the Agency: “The RED fails to provide empirical evidence that 

use of sulfometuron methyl herbicides in accordance with the current label causes harm 

to aquatic vegetation.” 

EFED Response # 5. 

With respect to aquatic vegetation, the RED is based on standard risk assessment 

methods used by the Agency for assessing ecological risks to non-target ecological 

receptors, including aquatic plants. This methodology, which relies on predicted 

concentrations in surface water based on maximum labeled rates, indicates potential risks 

to both vascular and non-vascular aquatic plants. These findings are consistent with the 

mode of action of sulfometuron methyl and results from risk assessments of other 

sulfonylurea herbicides. Consistent with risk findings for non-target aquatic plants, 

potential risks were also identified for non-target terrestrial plants. While empirical 

evidence (e.g., ecological incident reports) are considered in the characterization of 

ecological risks, such reports are likely subject to considerable bias (i.e., underreporting) 

particularly for ecological receptors for which adverse effects are rarely documented 

(e.g., aquatic plants). Therefore, lack of empirical evidence (e.g., ecological incident 

reports) does not supplant findings from other aspects of the Agency’s standard 

ecological risk assessments. As a point of reference, more than a dozen ecological 

incident reports classified as “probable” were associated with registered uses and effects 

on terrestrial non-target plants. 

******** 

Comment Group 6. 

SUMMARY OF COMMENTS: 

The Agency received several comments regarding the appropriateness of the AgDRIFT 

model for this risk assessment. Additional comments were also received regarding the 

inputs EPA used in the AgDRIFT modeling scenario, such as wind speed, application 

equipment, or droplet size, noting that the inputs are overly conservative and do not 

reflect typical application variables. 

EFED Response # 6. 

A noted above, AgDRIFT is an Agency approved, vetted model that 

is appropriate for evaluation of the factors being considered to reduce the impacts of 

spray drift from sulfometuron methyl use. In response to the RED comments, EFED has 

modeled a variety of realistic scenarios to determine how the amount of drift at various 

distances from the treated area can be reduced. Regarding comments on the application 
11

equipment (typically fixed wing for applications of fertilizer and sulfometuron methyl 

and rotary craft for just sulfometuron methyl), and droplet size the Agency has modeled a 

variety of realistic scenarios to determine how the amount of drift at various distances 

(based on different input combinations) can reduce environmental exposure. 

 

EFED has evaluated the reductions in drift from applications with coarser droplet size 

and wind speeds down to 10 mph based upon recommendations from commenters and 

discussions with stakeholders. Based upon its work, over the years, regarding modeling 

aerial applications, the Agency does not believe it is practical to limit applications to 

wind speeds below 10 mph. The Agency has not evidence that stetting a maximum wind 

speed of 7 mph (or even less) can be consistently followed. Therefore, the Agency has 

determined that a maximum wind speed of 10 mph is the lowest wind speed that can be 

enforced and consequently uses it as the default wind speed for modeling. 

We have rerun AgDRIFT with many scenarios using rotary aircraft (helicopter), ground 

applications, droplet size spectrums ranging to extremely course classifications, etc. We 

have seen no evidence that setting a maximum wind speed of 7 mph (or even less) can be 

consistently followed by the end-user; the Agency has determined at the current time that 

a maximum wind speed of 10 mph is the lowest maximum level that can be enforced. 

The Agency will review any additional submitted spray drift studies that are relevant, and 

modify the sulfometuron methyl label based upon these data if appropriate. 

******** 

Comment Group 7. 

SUMMARY OF COMMENTS: 

This comment stated that the current regulatory studies already “adequately addresses 

reproductive risk to non-target plants.” 

EFED Response # 7. 

While toxicity data were available for endpoints related to systemic growth, seedling 

emergence and visual injury, these guideline studies are not designed to capture 

reproductive endpoints. The Agency is aware of evidence to suggest plant reproduction 

may be affected by sulfonylurea herbicides at levels below effects on vegetative growth 

or visual injury (Fletcher et al., 1993)3

. Uncertainty regarding the potential greater 

sensitivity of terrestrial plant reproduction has been discussed extensively in the 

environmental fate and effects assessment for chlorsulfuron (D330621). Consistent with 

the Data Call-In for chlorsulfuron, the Agency is requesting a study to address the 

sensitivity of terrestrial plant reproduction to sulfometuron methyl. 

 

3

 Fletcher, J.S., T.G. Pfleeger, and H.C. Ratsch. 1995. Chlorsulfuron influence on garden pea reproduction. 

Physiol. Plantarum 94: 261-267. 
12

APPENDIX 1: Text of Comments being responded to in This 

Document 

The relevant excerpts from stakeholder comments on the Sulfometuron Methyl RED 

being responded to in this document are provided below (the OPP Divisions asked to 

respond are followed by the docket numbers from which the comments originate are 

provided in parenthesis). 

1. EFED, OGC. (Docket #131, 17, 22, 102, 75) 

SUMMARY OF COMMENTS: EPA received several comments regarding the term 

“under the forest canopy” noting that the phrase is vague and confusing. 

On page 32 of the RED, under Environmental Hazards the term except “under the forest 

canopy” was added. This term is very vague, open to interpretation, and accomplishes 

nothing but confusion in the context of the sentence it was added to. 

__ 

The definition of the phrase, "forest canopy" is too broad. 

___ 

On page 32 of the RED, under Environmental Hazards the term except “under the forest 

canopy” was added. This term is very vague, open to interpretation, and accomplishes 

nothing but confusion in the context of the sentence it was added to. This term should be 

clarified, dropped or re-worded. 

___ 

The phrase “...under the forest canopy...” vague, leaving this recommendation open for 

interpretation and will cause confusion among applicators and regulators alike. Is the 

intent to allow application to water when working under a forest canopy? What defines a 

“forest canopy”? 

___ 

Under Environmental Hazards (pg. 32 of 42) the statement “except for under forest 

canopy” is confusing. How is this meant to be interpreted? 

2. EFED, SRRD, RD 

SUMMARY OF COMMENTS: 

The Agency received comments that the current label language regarding “light sandy 

soil” does not provide useful application information. 

Non target plant exposure through soil particle drift wind erosion drift. 

 

“...applications are made to powdery dry soil or light sandy soil.” More specifics could 

be included here as you are referring to soils that are subject to wind erosion. Forest 

soils that have an intact forest floor are not subject to wind erosion. “Light sandy soil,” 
13

is not a soil texture class as defined by the U.S. Department of Agriculture classification. 

Soils that are subject to wind erosion have high silt, very fine and fine sand textural 

fractions. Low organic matter is another factor that can increase a soil’s wind erosion 

potential.

3. EFED (#131, 17) 

SUMMARY OF COMMENTS: 

The Agency received comments stating that the term “aquatic plants” is too vague and 

does not provide useful application information. 

The definition of the phrase, "aquatic plants" is too broad. 

__ 

“Do not apply within 500 feet of aquatic vegetation, water used as an irrigation source 

and crops.” is not a scientifically based conclusion and will be very difficult to comply 

with in practice. For one, define aquatic vegetation? By itself, this is a very vague term 

that only a botanist could define accurately. I would interpret this to mean that I would 

have to put a 500 foot buffer around any fish bearing stream or any intermittent stream 

or channel that may contain an aquatic plant or something that looks like an aquatic 

plant? What about a small inconsequential ground seep within a 40 acre clear-cut that 

contains aquatic vegetation. Am I required to identify and protect such areas with a 500 

foot buffer? With the preponderance, in Western Oregon, of streams and side channels 

feeding these streams on a seasonal basis, I would interpret this label requirement to 

mean that I shouldn’t spray within 500 feet of any of these topographic features to avoid 

a label violation. 

4. EFED (#24, 73, 21, 63, 166, 137, 112, 120, 102, 105, 171, 170, 165, 155, 79) 

SUMMARY OF COMMENTS: 

The Agency received numerous comments regarding the “release height” modeled and 

cited on the product label. Commenters noted that in commercial forestry scenarios, a 10 

foot release height is often unsafe. As an example, it was noted by one respondent that, 

in Washington state forestry application areas are “1) located in mountainous terrain and 

2) have scattered wildlife trees (required by state forest practice rules) in them.” Several 

commenters noted support for language that provided for safety without mandating a 10 

foot release height. 

The proposed label change requiring a maximum aerial application height of 10 feet for 

forestry applications is completely unfeasible for two main reasons. Forestry herbicide 

application areas in Washington are 1) located in mountainous terrain and 2) have 

scattered wildlife trees (required by state forest practice rules) in them. These two factors 
14

make it impossible and extremely unsafe for pilots to maintain this height above the 

ground. 

___ 

We believe that the prohibition on aerial applications more than 10 feet above the canopy 

is not only unnecessary, but can create hazardous operating conditions. Spray nozzle 

height is only one of many variables that affect spray drift, and operators should be 

allowed discretion in determining spray height as long as other conditions are such that 

drift prevent ion objectives can be met. Retention of tall snags and green trees are often 

required or encouraged by forest practice regulations or certification programs. Given 

the conditions on most forest sites where we prescribe aerial applications, we feel that 

excessive constraints on professional knowledge and judgment of trained applicators and 

pilots may create hazardous conditions and be counter-productive to effective 

applications. 

___ 

Your proposed requirement to prohibit application above 10 feet is not achievable with 

any margin of safety. Terrain that is too steep and/or has obstacles such as small 

branches will cause accidents for any pilots that try to comply with this requirement. 

___ 

The flying height restriction is an unnecessary addition to the label that could also be 

construed as dangerous. Flying an agricultural aircraft over rugged terrain can be even 

more hazardous when trying to fly excessively low. There are many small trees, snags 

and other obstructions that are dangerous to work around in spray treatment areas. 

Modern spray systems are designed to release the droplets at a safe height above the 

vegetation so that swath deposition is even across the ground. This system was designed 

for right of way applications and produce minimal fine droplets. Low flying should not be 

regulated with label language, let the pilot decide what is safe, prudent and produces the 

best application.

=========== 

We also note that the mitigation measures recognize that the 10-foot maximum does not 

apply if "a greater height is required for aircraft safety." However, the RED establishes 

10 feet as the regulatory norm, with the potential that deviations will be difficult to 

justify. We recommend the label require that spray height be the minimum level that 

meets safety standards and drift prevention objectives. Any reference to 10 feet should be 

limited to level areas of relatively uniform canopy height. 

__ 

Prohibition of aerial forestry applications more than 10 feet above the canopy is 

inherently dangerous. The “canopy” in forestry herbaceous weed control treatments is 

virtually ground level. Operators should be allowed discretion in spray height so long as 

other conditions allow accurate deposition of the spray mixture. Aerial forestry 

applications use helicopters. Low airspeed and use of drift control booms and nozzles 

(e.g. Accu-Flo nozzles) produce coarse droplet sizes with few fine droplets subject to 

drift. Drift control booms and nozzles do not develop an acceptable spray pattern at 10 

feet of altitude. The remedy, use of older boom and nozzle technology, would create more 

fine droplets and negate the perceived benefit of low altitude. The proposed measure will 
15

only serve to increase the potential for the greatest risk to the environment and to safety, 

an aircraft accident. 

___ 

Safety of our staff and operators is paramount to our business. The imposition of a fixed 

10-foot height above the canopy for aerial applications is highly unsafe under normal 

application conditions which include flying over trees with heights that vary by much 

more than 10 feet. In addition to the risk this poses on operators, enforcement and 

compliance of such a requirement will be challenging. I would encourage the EPA to 

change this language to include provisions for safety. 

We also note that the mitigation measures recognize that the ten-foot maximum height 

during aerial application does not apply if “a greater height is required for aircraft 

safety.” However, the RED establishes ten feet as the regulatory norm, with the potential 

that deviations will be difficult to justify. The imposition of a fixed ten-foot flight-height 

above the canopy for aerial applications would be highly unsafe under normal 

application conditions, which include flying over trees with heights that vary by much 

more than ten feet. We recommend the label require that spray height be the minimum 

level that meets safety standards and drift prevention objectives. 

___ 

“Spray must be released at the lowest height consistent with pest control and flight 

safety. Do not release spray at a height greater than 10 feet above the crop canopy unless 

a greater height is required for aircraft safety.” 

___ 

Flight Height. We note that the mitigation measures recognize that the 10-foot maximum 

does not apply if "a greater height is required for aircraft safety." However, the RED 

establishes 10 feet as the regulatory norm, with the potential that deviations will be 

difficult to justify. Spray height is only one of many variables that affect spray drift, and 

operators should be allowed discretion in determining spray height as long as other 

conditions are such that drift prevention objectives can be met. Moreover, sustainable 

forestry practices require that individual trees or groups of trees are left on a site for 

various reasons after harvest. The "canopy" would then consist of the growing trees of a 

uniform height, punctuated by much higher "leave" trees. 

___ 

Finally, we endorse the proposed label language addressing aerial application height 

(page 34 of the RED) in which operators are allowed to apply sulfometuron methyl at 

heights greater than 10 feet above the canopy if a greater height is required for safety. 

Clearly, a requirement for applications to be 10 feet or less above the canopy can create 

hazardous operating conditions in some locations. However, we would like to point out 

that spray height is only one of many variables that affect spray drift, and operators 

should be allowed discretion in determining spray height as long as other conditions are 

such that drift prevention objectives can be met, even if safety is not the primary goal for 

such an adjustment. Many companies attempt to bunch leave trees (for wildlife) in 

riparian corridors or other distinct locations to allow lower aerial applications of 

chemicals, but forest sites are often steep and have significant “roughness, ” which may 

require applications at greater heights. Current application methods are resulting in 

infrequent and minimal delivery of forest herbicides to streams, including sulfometuron 
16

methyl. 

___ 

The notion that restriction of aircraft to within ten feet of a forest canopy is a recipe for 

crashing aircraft, and for locally damaging impact both from fuel and concentrated 

herbicide spill, but also with loss of life and aircraft. It makes no sense, and does not 

properly reflect any demonstrated improvement in targeting of chemical so long as large 

drops are specified. Please drop this stipulation. 

___ 

The proposed label restriction for spray release height is hazardous. A vast majority of 

forestry application sites have uneven terrain and numerous standing trees. Aerial 

application on these sites cannot be safely done under the 10 foot restriction. Pilots must 

be allowed flexibility in establishing safe release height thresholds and be allowed to 

employ other suitable methods to reduce drift. 

___ 

EPA’s proposal to prohibit aerial applications more than 10 feet above the canopy is 

similarly unsupported by the record for the reasons discussed above, is impractical, and 

will result in hazardous operating conditions. There is no evidence that current spray 

height practices have created problems or concerns (indeed, EPA notes that most of the 

reported incidents involving this herbicide do not appear to involve aerial application at 

all, much less being traceable to spray height issues). As noted by NCASI and other 

commenters, forest sites are often characterized by uneven terrain and varying canopy 

heights, making it difficult, impractical, and unsafe to attempt to maintain a 10 foot spray 

height. The fact that the proposed spray height restriction is qualified by the statement 

that it does not apply if “a greater height is required for aircraft safety” does not resolve 

this issue. It will still create regulatory pressure to fly at unsafe low levels, and creates 

uncertainty and the potential for future disputes over when such a “greater height” 

would be justified. 

___ 

We also note that the mitigation measures recognize that the 10-foot maximum does not 

apply if “a greater height is required for aircraft safety.” However, the RED establishes 

10 feet as the regulatory norm, with the potential that deviations will be difficult to 

justify. Even a flat harvested site will have various snags and other trees remaining that 

will present hazards at 10 feet. 

We recommend the label require that spray height be the minimum level that meets safety 

standards and drift prevention objectives. Any reference to 10 feet should be limited to 

level areas of relatively uniform canopy height. 

5. EFED. (#132). 

SUMMARY OF COMMENTS: 

This comment was received by the Agency: 

The RED fails to provide empirical evidence that use of sulfometuron methyl herbicides 

in accordance with the current label causes harm to aquatic vegetation. 
17

6. EFED (#165, 134, 46, 27, 35, 36, 102, 155). 

SUMMARY OF COMMENTS: 

The Agency received several comments regarding the appropriateness of the AgDRIFT 

model for this risk assessment. Additional comments were also received regarding the 

inputs EPA used in the AgDRIFT modeling scenario, such as wind speed, application 

equipment, or droplet size, noting that the inputs are overly conservative and do not 

reflect typical application variables. 

We believe the AgDRIFT model used to estimate spray drift over-predicts drift, and that 

the input parameters of wind speed and droplet size are unrealistic. As a result the model 

outputs are unrealistic and over estimate drift potential. 

--------------- 

With help, I was able to locate the information about how the AgDrift model was applied 

to this RED that resulted in 500 foot buffers for aerial spraying. In short, the inputs to the 

model in no way represent the past 5-10 years real world use of SMM here in the Pacific 

Northwest. That is why we have had not had incidents in damaging buffer vegetation, 

much less damage to aquatic vegetation. Therefore these huge buffers are not needed. 

Errors in the AgDrift model parameters 

1) In the RED use of the AgDrift model, the first things that are not correct are: the use of 

a fixed wing aircraft that flies at 2- 3 times as fast as the helicopters that are required to 

be used by the present label! The only use of fixed wing aircraft on the Oust XP label is 

for the application of dry fertilizer that has been impregnated with Oust XP. Period. For 

all liquid spray uses, helicopters are required. 

2) The nozzle type selected for the AgDrift calculations were characterized as “Fine” 

droplet generators. While this may be allowed by the label, our usage is exclusively in 

utilizing nozzles such as the Accu-Flo® nozzles and others that result in spray droplet 

spectra which are characterized as Coarse or Ultra Coarse by the American Society of 

Agricultural and Biological Engineers (ASABE) Standards. 

3) The airspeed of the Ag Tractor was not given but again, it is much faster than a 

helicopter, resulting in orders of magnitude greater numbers of fine, driftable droplets. 

4) The wind speed in the model was 15 mph towards the off target line in the model. 

a. Our forest practices allow a maximum wind speed of only 7 -10 mph depending upon 

the state. 

b. The Oust XP label recommends that applications be made in winds less than 10 mph. 

c. Actual practice is that virtually all applications are made in winds from 3-7 mph and 

even lower when the wind is in the direction of a sensitive riparian area! 

___ 

The drift model used to estimate drift as far as 900 feet from the application does not 

reflect the current applications, equipment or observed effects on treated sites. 

___ 

The Ag-drift study from New Mexico is not pertinent to modern helicopter applications 
18

using low drift booms and special nozzles creating ultra coarse droplets greater than 

1000 microns without the creation of fine droplets. These large drops fall like rain and 

pose no hazard that hasn't already been addressed with the current label restrictions and 

state regulations. 

___ 

The second reason for not changing the label is that the Ag-drift model that is cited in 

EPA research is not applicable to 21st century aerial applications in Pacific Northwest 

timberlands. We use large droplets >1000 microns with technology not used in the AGDrift study.

Since a lot of the RED recommendations are based on spray drift modeling it is critical 

that the latest spray drift model is used. The RED refers to the use of the AgDrift® 

model. 

I believe there are more advanced versions available, e.g., AGDISP v 8.15. 

-------------------- 

The AgDrift model requires a complex level of inputs and is predominantly geared 

towards flat land agriculture applications. Forest applications in Western Oregon are 

typically on terrain that varies from mildly sloping to very steep. 

___ 

EPA’s proposal to require 500 foot buffer zones for aerial application and 100 foot 

buffer zones for ground application are based on overly conservative modeling 

projections that do not reflect typical use conditions and ignore contrary evidence in the 

record. 

7. EFED/SRRD (#116) 

SUMMARY OF COMMENTS: 

This comment stated that the current regulatory studies “adequately addresses 

reproductive risk to non-target plants.” 

the request by the Agency to provide .a special study to "evaluate reproductive risk to 

non-target plants exposed to small droplets of sulfometuron" 

DuPont believes that the current regulatory studies submitted in support of sulfometuron 

methyl registration adequately addresses reproductive risk to non-target plants for the 

following reasons: 

• Phytotoxicity data from regulatory testing based on vegetative endpoints are sufficiently 

sensitive to be protective of potential yield effects in non-target plants 

• The studies conducted for regulatory testing are conducted on 10 diverse plant species 

that represent a range of responses that are representative of plants in general 

(McKelvey et a12002) 

• The lowest EC25 endpoints, reflect the most sensitive endpoint on the most sensitive 

species, therefore, using this endpoint in the risk assessment will likely be protective to 

most plants.
19

APPENDIX 2: Documentation of Spray Drift Modeling 

Sample AgDRIFT Input Screens

File Name: AgDrift Sulfomtrn Tier2 Heli_H10_W10_VCoars_AR0281.agd 

File Name: 

Grnd Nonvol 0.375, Active 0.281, h4.2_w10_d-Fn-Med 
20

Sample AgDRIFT Input File

File Name: AgDrift Sulfomtrn Tier2 Heli_H10_W10_V-ExCrs_AR0281.agd 

AGDRIFT_userdata 

 3 

 2 

 0 

 0 

Novol 0.375, Active 0.281, h10_w10_d-VrtoExCrs 

 1 

 3 

 20 

 0 

 1 

 20 

 0 

 10 

ASAE Very Coarse to Extremely Coarse 

 36 

 23 

 54.5 0.001 

 63.16 0.001 

 73.23 0.0017 

 84.85 0.0023 

 98.12 0.0037 

 113.71 0.0057 

 131.73 0.0063 

 152.79 0.008 

 177.84 0.013 

 205.84 0.0207 

 238.45 0.0337 

 276.48 0.0413 

 320.6 0.048 

 372.18 0.055 

 430.74 0.078 

 498.91 0.139 

 578.54 0.1647 

 670.72 0.1477 

 777.39 0.1037 

 900.61 0.0647 

 1044.42 0.036 

 1210.66 0.0167 

 1403.04 0.0083 

 0 

 0 

 4 

ASAE Fine to Medium 

 40 

 31 

 10.77 0.001 

 16.73 0.000333 
21

 19.39 0.000667 

 22.49 0.000333 

 26.05 0.000667 

 30.21 0.001 

 35.01 0.001 

 40.57 0.002 

 47.03 0.003333 

 54.5 0.005333 

 63.16 0.006667 

 73.23 0.009 

 84.85 0.013333 

 98.12 0.022333 

 113.71 0.033 

 131.73 0.039333 

 152.79 0.048 

 177.84 0.064667 

 205.84 0.083 

 238.45 0.114667 

 276.48 0.128333 

 320.6 0.138 

 372.18 0.112667 

 430.74 0.064 

 498.91 0.044 

 578.54 0.031667 

 670.72 0.020333 

 777.39 0.009333 

 900.61 0.001 

 1044.42 0.000667 

 1210.66 0.000334 

 0 

 0 

 4 

ASAE Fine to Medium 

 40 

 31 

 10.77 0.001 

 16.73 0.000333 

 19.39 0.000667 

 22.49 0.000333 

 26.05 0.000667 

 30.21 0.001 

 35.01 0.001 

 40.57 0.002 

 47.03 0.003333 

 54.5 0.005333 

 63.16 0.006667 

 73.23 0.009 

 84.85 0.013333 

 98.12 0.022333 

 113.71 0.033 

 131.73 0.039333 

 152.79 0.048 

 177.84 0.064667 

 205.84 0.083 
22

 238.45 0.114667 

 276.48 0.128333 

 320.6 0.138 

 372.18 0.112667 

 430.74 0.064 

 498.91 0.044 

 578.54 0.031667 

 670.72 0.020333 

 777.39 0.009333 

 900.61 0.001 

 1044.42 0.000667 

 1210.66 0.000334 

 0 

 0 

 0 

CP 

 2 

 0.061 

 44.7 

 30 

 4.137 

 0 

 0 

 0 

CP 

 2 

 0.061 

 44.7 

 30 

 4.137 

 0 

 0 

 0 

CP 

 2 

 0.061 

 44.7 

 30 

 4.137 

 0 

 0 

 1 

D4-45 

 5 

 280.3 

 0.9578 

 0.11 

 65 

 1 

IWS-0069 

 8 

 73 

 1 

 0.997 
23

 3 

 44.7 

 45 

 4.137 

 0 

 0 

 0 

 0 

 1 

D4-45 

 5 

 280.3 

 0.9578 

 0.11 

 65 

 1 

IWS-0069 

 8 

 73 

 1 

 0.997 

 3 

 44.7 

 45 

 4.137 

 0 

 0 

 0 

 0 

 1 

D4-45 

 5 

 280.3 

 0.9578 

 0.11 

 65 

 1 

IWS-0069 

 8 

 73 

 1 

 0.997 

 3 

 44.7 

 45 

 4.137 

 0 

 0 

 0 

 0 

 1 

Water 

 40 

 2.245552E-02 
24

 1.682667E-02 

 18.71 

 1 

 1 

 84.76 

 0 

 2 

Wasp Helicopter 

 40 

 4 

 5.3036 

 27.714 

 0 

 947.6309 

 0 

 320 

 0 

 0.8 

 0 

 0 

 1 

 0 

 0 

-2.8408 

 0 

 0.1 

 0 

 2 

Nozzles for Wasp Helicopter 

 40 

 27 

 0 -3.861 0 0 

 0 -3.531 0 0 

 0 -3.2 0 0 

 0 -3.035 0 0 

 0 -2.87 0 0 

 0 -2.54 0 0 

 0 -2.21 0 0 

 0 -1.88 0 0 

 0 -1.549 0 0 

 0 -1.219 0 0 

 0 -0.864 0 0 

 0 -0.698 0 0 

 0 -0.368 0 0 

 0 -0.038 0 0 

 0 0.292 0 0 

 0 0.698 0 0 

 0 0.864 0 0 

 0 1.219 0 0 

 0 1.384 0 0 

 0 1.88 0 0 

 0 2.21 0 0 

 0 2.54 0 0 

 0 2.87 0 0 
25

 0 3.035 0 0 

 0 3.2 0 0 

 0 3.531 0 0 

 0 3.861 0 0 

 0 

 72.8 

 4.4704 

-90 

 2 

 30 

 50 

 1013 

 0.56 

 0.0075 

 0 

 

 0 

 0.02 

 494.2088 

 0 

 1 

 24.32 

 2.57 

 0.426 

 1.856 

 0 

 30 

 50 

 0.14 

 0.7 

 0 

 0 

 0 

 0 

 3.048 

 20 

 0 

 18.2882 

 0 

 0.3702 

 0 

 0 

 0 

 600 

 795 

 0 

 0