UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

MAR _ 1 7 20111 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

MEMORANDUM 

SUBJE~T: 

FROM: 

THRU: 

TO: 

Sodium Acifluorfen: Usage Information and Proposed Herbicide Resism:ice{) ~ "'""-

Management Measures (PC# 114402). ~~ f<--"-'. • d 

Sunil Ratnayake, Ph.D., Biologist L , . c W;IJ . C~ ' l 

William Chism, Ph.D., Senior Biolo · / · ~ n( / •hk ' ~ 

Jonathan Becker, Ph.D., Senior Science Advisor J/,'lc.LJ ~ 'of{ 7]0,, 1""""~ Biological Analysis Branch --

Economic 

Stephen Smearman

Analysis 

, 

Branch 

Economist ~~ 

Biological and Economic Analysis Division (7503P) 

Biological 

Colwell Cook

Analysis 

, Ph.D., 

Branch 

Acting Branch Chief 

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· fl/lf:A.f!A 

)" O N fl.. 

~ 

~o l w/)).. ~ k__ 

Timothy 

Economic Kiely, Analysis 

Chief 

Branch 

u ~ 

Biological and Economic Analysis ivision ( P) 

Nathan Sell, Chemical Review Manager 

Kelly Sherman, Chief 

Risk Management and Implementation Branch III 

Pesticide Reevaluation Division (7508 P) 

BEAD Product Review Panel Date: March 2, 2016 I 

Page 1 
SUMMARY 

This document describes the use and usage of the herbicide sodium acifluorfen which is 

undergoing registration review in the pffice of Pesticide Programs (OPP). 

Sodium acifluorfen was first registered as a pesticide in the U.S. in 1980 (USEPA, 2004). It is a 

selective herbicide used for the control of broadleaf and grass weeds. Depending on the crop, 

sodium acifluorfen is applied as pre or post emergence treatments at different growth stages of 

crops such as soybeans, peanuts, rice, and strawberries. It is a valuable herbicide for the control 

of weeds in peanuts with 17% of the crop treated annually. While aerial application is pennitted 

on all registered crops, Market Research Data indicate that sodium acifluorfen is applied aerially 

only on rice and soybeans. Aerial applications on rice and soybeans accounts for 10% of the 

total acres treated with sodium acifluorfen per y~ar. 

To address the spread of herbicide resistant weeds the Agency is proposing weed resistance 

management elements during the registration review process. This is a tiered approach where 

the situations (i.e. the interaction of the mechanism of action, resistant weeds, and weed 

management strat~gies) with the least concern for herbicide resistant weeds will have the fewest 

number of resistance management elements and the situations with the highest concern will have 

the most resistance management elements. 

In addition to the sodium acifluorfen docket, a PRN will be issued shortly to provide guidance to 

registrants on the Agency's herbicide resistant management approach. All stakeholders are 

encouraged to submit comments. Public comments received from the chemical specific docket 

will be considered prior to the Agency's final decision on sodium acifluorfen. 

Sodium acifluorfen acts to inhibit the protoporphyrinogen oxidase (PPO) enzyme, a key enzyme 

in the production of precursor molecules needed for photosynthesis. PPO inhibitors also result in 

the formation of highly reactive molecules that attack and destroy lipids and protein membranes. 

This herbicide is classified by the Weed Science Society of America (WSSA) as belonging to 

mechanism of action (MOA) Group 14. This MOA has three confirmed herbicide resistant 

weeds. 

This MOA is of moderate concern for weed resistance development because of the existing cases 

of confirmed herbicide resistant weeds. Currently there are no herbicide resistant crops. 

Proposed herbicide resistance management elements for sodium acifluorfen are described herein. 

BACKGROUND 

FIFRA Section 3(g) mandates that EPA periodically review the registrations of all pesticides to 

insure that they do not pose unreasonable adverse effects to human health and the environment. 

This periodic review is necessary in light of scientific advancements, changes in policy, and 

changes in use patterns that may alter the conditions underpinning previous registration 

decisions. In determining whether. effects are unreasonable, FIFRA requires that the Agency 

consider the risks and benefits of any use of the pesticide. 

Page2 
OPP has completed human health and ecological risk assessments for sodium acifluorfen. No 

human health ri.sks were identified. Ecological risks were evaluated for non-target plant species, 

fish and birds. For non-target plant species, risks were found in areas adjacent to treated fields 

due to spray drift. Aerial applications typically pose the greatest risk since the drift is more likely 

and more widespread. Other variables that may affect risk drivers in the risk assessment include 

application rates, droplet size, and boom height. 

Sodium acifluorfen was first registered as a pesticide in the U.S. in 1980 (USEPA, 2004). The 

registration review docket for sodium acifluorfen (EPA-HQ-OPP-2010-0135) opened in March 

2010. Sodium acifluorfen is a selective, post-emergent contact herbicide registered for use to 

control annual broadleaf weeds and some grasses in soybeans, rice, peanuts, and strawberries. 

There are currently no registered residential uses. Sodium acifluorfen is a member of the 

di phenyl ether group of herbicides and it belongs to a class of compounds, light dependent 

peroxidizing herbicides (LDPH), known to have a phototropic mode of action in plants. LDPHs 

act in plants through inhibition of the enzyme protoporphyrinogen oxidase, leading to cell 

membrane disruption through reactive oxygen species in the presence of light. The registered 

sodium acifluorfen products are liquid concentrates, which are applied using ground or aerial 

equipment. Also, sodium acifluorfen is formulated or packaged with other herbicides, such as 

bentazon, imazaquin, sethoxydim, or glyphosate. Sodium acifluorfen can be applied using an 

aircraft, boom sprayer, and other ground application equipment. 

USAGE 

Sodium acifluorfen is applied to approximately one million acres of cropland annually in the 

United States (Market Research Data, 2010-2014). The crops that are most dependent on sodium 

acifluorfen in terms of average percent crop treated (PCT) include peanuts (17%) and rice (5%). 

For soybeans about 1% of the crop is treated on average which accounts for about 800,000 acres 

of the one million acres treated annually with sodium acifluorfen. For the years 2013 and 2014, 

reported use of sodium acifluorfen use on soybeans has increased dramatically. The number of 

soybean acres treated increased to approximately 2.2 million acres in 2014 compared to 

approximately 200,000 thousand treated in 2012. 

In terms of pounds applied, between 2004 and 2012, the average annual pounds (lbs) active 

ingredient (AI) applied were as follows: peanuts (50,000 lbs Al/year), rice (20,000 lbs Al/year), 

and strawberries (500 lbs AI/year). For soybeans the average pounds applied from 2004 to 2012 

was 80,000 lbs AI/year. However, the average number of pounds applied for soybeans over the 

time period from 2010 to 2014 jumped to 800,000 lbs AI/year reflecting substantial increases in 

the number of pounds of active ingredient applied in 2013 and 2014. 

During the 2004 to 2012 time period., on average, one application of sodium acifluorfen was 

applied per year to these registered uses. More recently, between the years 2009 to 2013, 2.5% 

of treated peanuts, 4.6% of treated rice, and 10% of treated soybeans, received an annual average 

of two applications. Information on the use of sodium acifluorfen is presented in Table 1. 

Page3 
Table 1. Sodium Acifluorfen: Average versus Maximum Number of Applications and 

A lication Rates 

Peanuts 1,228,001 209,634 17 0.375 0.240 

Rice 2,878, 190 120,254 5 0.183 

Rice 0.25 

Arkansas 1,356,795 86,749 6.5 0.188 

Soybeans 78,243,010 866,550 0.375 0.265 

Strawberries 58,000 55 <I 0.354 

Strawberries 

0.375 

·chi an 720 55 8% 0.354 

Market Research Data, 2010-2014. Numbers have been rounded. 

*EPA, EFED Label Data Report, 2009 

Table 2 below provides information on aerial applications for sodium acifluorfen. While aerial 

application is permitted for all labeled crops, Market Research Data indicate that sodium 

acifluorfen is applied aerially to two crops only, rice and soybeans. Aerial application to rice and 

soybeans accounts for 10% of the total acres treated with sodium acifluorfen per year. Most of 

the aerial applications of sodium acifluorfen are made on rice with an average of up to 83,000 

acres treated annually. This accounts for approximately 70% of the acres treated aerially with 

sodium acifluorfen annually from 2010-2014. For soybeans, aerial applications are made on 

about 33,000 acres treated on average, which· accounts for the remaining 30% of the acres treated 

aerially with sodium acifluorfen annually from 2010-2014 (Market Research Data, 2010-2014). 

On average, 4% of the sodium acifluorfen applied to soybeans is made aerially, while 

approximately 66% of the sodium acifluorfen applications to rice are made aerially. Aerial 

applications are made to accommodate wet or overgrown fields that are unable to be entered by 

foot or ground machinery. For weed control in strawberries, sodium acifluorfen is typically 

applied using ground equipment as a band application during renovation (over the top of straw 

mulch) or after transplanting the plants (before laying plastic mulch). 

Of all the rice acres treated aerially, Arkansas accounted for 75% of the rice aerial applications 

with sodium acifluorfen followed by Mississippi and Louisiana with about 12% each and Texas 

with approximately 2%. For ground applications, California accounted for approximately 85% 

of sodium acifluorfen applied to rice followed by Arkansas with 10%. 

Page4 
T a e bl 2 . P ercen t o o f S d1um . A Cl ·o UO rfi en T rea t e dB v A1r . . 

Average Average Average Percent Percent of the 

Crop Total Acres Acres Treated of Crop Acres Sodium 

Treated Aerially Treated Aerially Acifluorf en 

Applied Aerially 

Rice 125,488 82,831 66% 70% 

Rice (Arkansas) 90,820 67,745 75%* 60% 

Sovbeans 952,178 33,076 4% 30% 

Market Research Data, 2010-2014. 

*Arkansas rice acres treated aerially accounted for approximately 84% of the total rice acres with 

aerial treatments. 

Recommended Application Rates and Timing 

Sodium acifluorfen is applied on peanut as a pre-emergence treatment (before the emergence of 

crop) or early post and late post treatmens (after the crop emergence) with no more than 0.5 lbs 

AI applied per acre per season. 

For rice, the recommended application timing is from three leaf to early boot·stage (Acifluorfen 

2L Product label, 2012). The maximum application rate for rice is 0.25 lbs AI per acre per season 

(Acifluorfen 2L Product label, 2012). According to the label recommendation, sodium 

acifluorfen should not be applied on rice after the boot stage. This is a growth stage after the 

establishment of permanent flood and generally, permanent flooding is established 4 weeks after 

planting. Not more than two applications should be made on rice per season. Prior to 

application, the rice crop must pass the 3-leaf stage. On the basis of Market Research Data, the 

highest amount of sodium acifluorfen applied on rice is for late post-applications, which is three 

weeks after planting or later. 

For soybean, sodium acifluorfen is applied as a pre-plant bum-down treatment prior to planting. 

In addition, sodium·acifluorfen is also applied on soybean at the early growth stage of weeds. 

This is mostly during the two to six leaf stage of weeds depending on the weed species. 

According to the product label, not more than 0.5 lbs AI per acre per season should be applied on 

soybean. The second application of sodium acifluorfen is as a late post application to manage 

new flushes of weed populations during the mid-season. According to Market Research Data the 

most usage of sodium acifluorfen on soybean is applied as late post applications, which is three 

weeks after planting or later. There must be a minimum of 15 day appFcation intervals between 

two applications. 

For weed control in strawberries sodium acifluorfen is applied as a band application after the 

final land preparation. However this application must be made before laying plastic mulch and 

transplanting the crop (Acifluorfen 2 Product label, 2012). On strawberries only ground 

equipment is used to apply sodium acifluorfen and the maximum application rate for 

strawberries is 0.375 lbs AI per season (Acifluorfen 2L Product label, 2012, Registration no. 

82534-2-88783). . 

Page 5 
Application Rates and Number of.Applications of Sodium Acifluorfen 

There were three crops to which sodium acifluorfen was applied multiple times per year between 

2010 and 2014. Peanuts, rice, and soybeans each had up to 2 applications per year. For peanuts, 

rice and soybeans, about 2%, 4.5% and 8% of the acres respectively, report two applications 

(Market Research Data, 2010-2014). Strawberries acres received only one application of sodium 

acifluorfen seasonally. The maximum, average and upper bound application rates and the 

percent of acres treated multiple times for peanuts, rice, soybeans and strawberries is presented 

in Table 3. 

In terms of the application rate for each crop, approximately 95% of the peanut acres are treated 

at a rate equal to or below 0.25 lbs Al per acre with an average single application rate of0.233 

lbs AI per acre well below the single maximum application rate of0.375 lbs AI per acre. For 

rice, approximately 70% of the acres are treated at a rate equal to or below 0.20 lbs AI per acre 

with an average single application rate of 0.175 lbs AI per acre which is also well under the 

maximum single application rate of 0.250 lbs AI per acre. For soybean, about 80% of the 

soybean acres are treated at a rate equal to or below 0.25 lbs AI per acre with an average single 

application rate of 0.241 lbs AI per acre, also well under the maximum single application rate of 

0.375 lbs AI per acre. For strawberry, approximately 70% of the strawberry acres that are 

treated with sodium acifluorfen, are treated at the single maximum rate of 0.375 pounds AI per 

acre. The average single application rate is 0.354 pounds AI per acre with 0% of the acres treated 

multiple times. All of the sodium acifluorfen use reported on strawberry is from Michigan. . 

The reported use and rates indicate that the majority of acres are treated at rates below the 

maximum (which are used in the risk assessments). Thus, the risks identified in the risk 

assessments are unlikely to be realized in field situations. (See Table 3) 

T a e bl 3 A . .pp Ii ca f 10 0 Ra tes an dMJ"JA u tip. e .pp Ii cations o f S o dmm " A c ifl uo rfi en b C 1y rop. 

*Maximum Single Average Single Upperbound Rate 

Crop Application Rate Application Rate (%of Acres 

(lbs Al/acre) (lbs Al/acre) Treated) 

-95% at 0.25 lbs 

Peanuts 0.375 0.233 AI/acre 

- 70% at 0.2 lbs 

Rice 0.250 0.175 AI /acre 

- 80% at 0.25 

Soybeans 0.375 0.241 lbs AI/acre 

- 70% at 0.375 lbs 

Strawberry 0.375 0.354 AI /acre 

Market Research Data, 2010-2014. Numbers have been rounded. 

*EPA, EFED Label Data Report, 2009 

Page6 

% of Acres 

Treated Multiple 

Times 

2.0% 

4.5% 

8% 

0% 
Target Pests of Sodium Acifluorfen 

Sodium acifluorfen controls many annual broadleafweeds such as momingglory (lpomea spp.), 

black nightshade (Solanum nigrum), cocklebur (Xanthium strumarium), ragweed (Ambrosia 

artemisiifolia), smartweed (Polygonum spp.), wild buckwheat (Polygonum convolvulus) and wild 

mustard (Sinapis arvensis) species (WSSA, 2014). Also, sodium acifluorfen at higher rates can 

be applied to control several grass weed species such as seedling johnsongrass and foxtail 

species (WSSA, 2014). 

Hemp sesbania (Sesbania exaltata), redstem (Ammannia baccifera), and barnyardgrass 

(Echinochloa crusgalli) are the most troublesome weeds in rice production. Sodium acifluorfen 

is recommended for common annual weed species found in the rice production fields, especially 

for the control of hemp sesbania, and redstem, (Texas Rice Production Guide Lines, 2014). 

Major weed species found in peanut production are morning-glory species (lpomoea spp.), Hemp 

sesbania (Sesbania exaltata), sicklepod (Cassia obtusifolia), and Palmer amaranth (Amaranthus 

Palmeri), (Market Research Data). 

Major weeds species found in soybean production are red root pigweed (Amaranthus 

retroflexus), morning glory (lpomoea spp.), common waterhemp (Amaranthus. rudis), hemp 

sesbania, and sicklepod. (Market Research Data). Some of these weed species are resistant to 

glyphosate and ALS inhibiting herbicides (He~p, 2016). In recent years, the use of PPOinhibitors has increased, especially for controlling glyphosate- and ALS-resistant weeds in 

soybean (Legleiter et al., 2009). 

Droplet Size and Efficacy of Sodium Acifluorfen 

The droplet size effects the efficacy and off site drift of a pesticide application. The optimum 

droplet size for any herbicide or plant growth regulator is not something that can be generalized; 

rather, it should be selected based on data and knowledge. Deposition of the most effective 

amount of active ingredient on pl~t foliage and reduction of off-site drift are the major 

objectives of selecting an optimum. droplet size. In some cases, droplet size and application rates 

are correlated; that is, coarser droplets are associated with higher application rates to maintain 

efficacy. However, in some systemic herbicides or defoliants, coarse droplet size with less 

coverage will still allow effective control. The optimum droplet size is impacted by 

chemical/physical parameters of the pesticide and other factors such as drying of the chemical 

prior to actual uptake and air pressure used in the application. In addition, the interaction of 

concentration and plant uptake, and th~ interaction of the active ingredient with other chemicals 

in a tank mixture are some of the other Jactors that should be considered on selection of optimum 

droplet size. BEAD has limited information on the relationship of droplet size and efficacy for 

sodium acifluorfen. 

RESISTANCE MANAGEMENT 

The development and spread of herbicide resistant weeds in agriculture is a widespread problem 

that has the potential to fundamentally change production practices in US agriculture. While 

Page7 
herbicide resistance weeds have been known since the 1950s, the number of species and their 

geographical extent, has been increasing rapidly. Currently there are 249 weed species 

worldwide with confirmed herbicide resistance, especially since the turn of the century. In the 

United States there are 155 weed species with confirmed resistance to one or more herbicid~s. 

Management of herbicide resistant weeds, both in mitigating established herbicide resistant 

weeds, and in slowing or preventing the development of new herbicide resistant weeds is a 

complex problem without a simple solution. Coordinated efforts of growers, agricultural 

extension, academic researcher, scientific societies, pesticide registrants, and state and federal 

agencies are required to address this problem. 

In September 2-014, the Weed Science Society of America sponsored an international meeting, . 

the Herbicide Resistance Summit Il, hosted by the National Research Council (WSSA, 2014). 

This meeting was organized to facilitate a more unified understanding of the herbicide resistance 

issues across the country, understanding of differences of viewpoints, and approaches to 

solutions. The meeting was attended in person or via webinar by participants from 

approximately 100 locations across the United States, Australia, Canada and Germany, 

underscoring the significance and widespread nature of this problem and its impact on 

agricultural productivity. 

The Agency announced at this meeting that it would take a more proactive role in developing 

regulatory approaches for managing resistant weeds (Housenger, 2014). Shortly after this 

meeting, the Secretary of A¢culture announced USDA's herbicide resistance actions that were 

developed in collaboration with the Environmental Protection Agency (USDA, 2014). 

The EPA, Office of Pesticide Programs (OPP) is proposing measures for the pesticide registrants 

to provide growers and users with detailed information and recommendations to slow the 

development and spread of herbicide resistant weeds. This is part of a more holistic, proactive 

approach recommended by crop consultants, commodity organizations, professional/scientific 

societies, researchers, and the registrants themselves. OPP's approach is measured, based on the 

inherent risk of weed resistance developing for a given herbicide, considering the target weeds 

and the agronomic practices of the registered crops. Situations with the least concern for the 

development of herbicide resistant weeds will have the fewest resistance management elements 

and the situations with the highest concern will have additional resistance management elements. 

Additional details are provide in the attached appendices, as follows: 

Appendix I - Guidance for Pe~ticide Registrants on Pesticide Resistance Management 

Labeling (EPA, 2001) 

. Appendix II-Definition of Resistance and Likely Resistance 

Appendix III - Best Management Practices for Herbicide Resistant Weeds (from the 

Herbicide Resistance Action Committee and the Weed Science Society of America . 

Page 8 
Implementation Timeline and Opportunities for Public Comment on Herbicide Resistance 

Approach 

OPP is proposing to implement herbicide resistance m~asures for existing chemicals during 

registration review, and to implement herbicide resistance measures for new chemicals and uses 

at the time of registration. In registration review, proposed herbicide resistance elements will be 

in every herbicide preliminary interim decision. Comments on these chemical specific measures 

are welcomed. In addition, OPP will issue a PRN that will provide registrants with addition 

guidance. All stakeholders are encouraged to comment on the herbicide resistance management 

approach, rationale, and proposed elements. 

Public comments received concerning the sodium acifluorfen docket and the PRN docket will be 

considered prior to the final decision on sodium acifluorfen. 

Herbicide Resistant Management Concerns with Sodium Acifluorfen 

Sodium acifluorfen acts to inhibit tl?.e protoporphyrinogen oxidase (PPO) enzyme, a key enzyme 

in the production of precursor molecules needed for the photosynthesis. PPO inhibitors also 

result in the formation of highly reactive molecules that attack and destroy lipids and proteins 

membranes. This herbicide is classified by the Weed Science Society of America (WSSA) as 

belonging to mechanism of action (MOA) Group 14. This MOA has three confirmed herbicide 

resistant weeds. 

This MOA is of moderate concern for weed resistance development because of the existing cases 

of confirmed herbicide resistant weeds. Currently there are no protoporphyrinogen oxidase 

(PPO) resistant crops. 

Therefore, registrants should address elements one through eight in Table 4. Table 4 lists the 

complete set of resistance management elements that can help slow the spread of herbicide 

resistant weeds and Table 5 indicates which elements should be addressed based on mechanism 

of action (MOA) and use on herbicide resistant crops. These elements include instructions for 

the user, label language, and instructions to the registrant. 

Page9 
Table 4. Elements of Resistance Manae:ement or Stewardship Plan. 

Element Description 

1 

2 

3 

4 

5 

6 

7 

8 

List Mechanism of Action (MOA) Group Number. 

• This information is critical to allow the user to rotate between effective 

MOA's to reduce the buildup of resistant pests. 

);> Registrant is responsible for placement on label. 

List seasonal and annual maximum number of applications and amounts. 

• This information is critical to allow the user to know how many 

applications and amounts can be applied in order to develop an effective 

IPM plan for the season and the entire year. 

);> Registrant is responsible for placement on label. 

Resistance Management language from PR Notice 2001-5, and/or 

Best Management Practices (appropriate to crop) from Weed Science Society of 

America (WSSA) & Herbicide Resistance Action Committee (HRAC), and/or 

HRAC proposed guidelines for herbicide labels. 

• This is an educational opportunity to remind users to look for and follow a 

resistance management plan. 

> Registrant is responsible for placement on label. 

User should scout before and after application. 

• Reminding the user to scout can help insure that the proper pesticide is 

applied based on the weed species and growth stage and determine if the 

pesticide applied provided effective control. · 

> Registrant is responsible for placement on label. 

> User is responsible for following the recommendations. 

Definition of Likely Resistance. 

• It can take up to five years to confirm herbicide resistance. By describing 

likely resistance users could proactively identify and attempt to control 

weeds in the early stages before they become widespread in their fields. 

> Resristrant is responsible for placement on label. 

User should report lack of performance to registrant or their representative. 

• Reporting lack of performance can help provide the user with additional 

resources for the identification and control of problem weeds. In some 

cases lack of performance could be an early indication of likely resistance 

and contacting the registrant can help insure the weed is controlled before 

resistance becomes widespread in their fields. 

> Registrant is responsible for placement on label. 

> User is responsible for following the recommendations. 

List confirmed resistant weeds in a separate table and list effective or 

recommended rates for these weeds with the table. 

• This is an educational opportunity to clearly indicate which weeds are 

prone to resistance and remind the users to select the correct rates for their 

crop and site. 

> Registrant is responsible for placement on label. 

Registrant report new cases of likely and confirmed resistance to EPA and users 

yearly. This will be in addition to any adverse effects reporting. 

• ·This will allow the information likely and confirmed resistance to be 

Page 10 
available in a timely manner to users, consultants, extension, etc. so that 

they are aware of and proactively address the problem. 

• Provide weed species, crop or site, state, and herbicide used . 

);> Recistrant is responsible for reporting. 

For sites of high concern provide growers with: 

0 Resistance Management Plan 

0 Remedial Action Plan (to control resistant weeds this season or next season) 

0 Educational materials on resistance management. 

9 • Plans should be locally developed and easily modified. EPA recommends 

that registrants work with Extension, Consultants, Crop Groups, HRAC, & 

USDA. 

• This is an educational opportunity to remind users of the importance of 

resistance management. 

);> Registrant is responsible for creating or providing educational materials. 

For combination products with multiple MOA, list which herbicide is controlling 

which weed (a 3 way mixture may only have 1 effective MOA for some problem 

weeds). List minimum recommended rate if resistance is suspected. 

• Using a combination products with only one effective MOA can select for 

10 herbicide resistant weeds. 

• This will allow users to select herbicide combinations with multiple 

effective MOAs for the problem weeds on their fields. 

• Registrant is responsible for placing the list on label or otherwise providing 

the information. 

Any additional specific requirements (e.g. mandatory crop rotation, unique 

agronomic aspects, additional training, time limited registration, etc.). 

• During discussions with the Agency other elements may be deemed 

11 appropriate to help reduces the spread of resistance. 

• The elements may be on the label, the technical use agreement for the seed 

trait, or as a reporting requirement. 

);> Rel?istrant is responsible. 

Footnote: Mechanism of Action Group number comes from the WSSA, definition of resistance 

and likely resistance, PR Notice 2001-5 and BMP language are in Appendix 1-3. 

Resistance elements for fungicides and insecticides. 

Page 11 
Table 5. Herbicide Resistance Catffones of Concern* 

MOA's with no 

resistance weed 

species in the U.S. 

1. MOA on Label 

2. List seasonal and 

annual maximum 

number of 

applications and 

pounds 

3. Resistance 

management 

language from 

PRN 2001-5 or 

BMPs 

4. Scout before and 

after application 

-- -

MOA's with a few resistant 

weed species in the U.S. 

Elements 1 through 4 plus 

5. Definition of likely and 

confirmed resistance 

6. Farmer should report 

lack of performanc.e to 

registrant or its agent 

7. List confirmed resistant 

species in separate 

table and list effective 

or recommended·rates 

for these weeds with 

the table 

8. Registrant report new 

cases of likely and 

confirmed resistance to 

EPA & users yearly 

,.. 

.. _ 

' -. 

Higfi eoncern .,, 

• Any new herbicide with a new or 

novel mechanism of action, or 

• Herbicides for which resistant 

crop(s) have been developed 

(conventionally bred or GM), or 

• MOA's with most resistant weeds 

in U.S. 

Elements 1 through 8) plus · 

9. Provide growers with: 

Resistance Management Plan, 

Remedial Action Plan, 

Educational materials on 

resistance management 

10. For combination products with 

multiple MOAs, list which 

herbicide is controlling which 

weed and minimum 

recommended rate 

11. Any additional specific 

requirements (e.g. mandatory 

crop rotation, unique agronomic 

aspects, time limited · 

relristration, etc.). 

* If new resistant weed species are found a MOA may move to higher level of concern. 

REFERENCES 

Acifluorfen 2L. Product Label (EPA Reg. No. 82534-2-88783). 2012. Summit Agro USA, LLC. 

8000 Regency Parkway Suite 285, Cary, NC 27518. Online Publication. Available at: 

http://www.agrian.com/pdfs/Acifluorfen 2L Label.pdf. Accessed on March 3, 2016. 

BEAD, 2014. Acifluorfen Screening Level Usage Analysis (SLUA). Biological and Economic 

Analysis Division, Office of Pesticide Programs, US Environmental Protection Agency. 

July 7, 2014. 

EPA. 2001. Guidance for Pesticide Registrants on Pesticide Resistance Management Labeling. 

Pesticide Registration (PR) Notice 2001-5. 

http://www.epa.gov/sites/production/files/20l4-04/documents/pr2001-5 .pdf. 

Fraser, K. 2013. Glyphosate resistant weeds intensifying. Accessed online on July 23, 2015 at 

http://stratusresearch.com/blog/glyphosate-resistant-weeds-intensifying . 

Page 12 
Heap, I. 2016. The International Survey ofHerbi id~ Resistant Weeds. Online. Internet. 

Tuesday, November 10, 2015. Available at: www.weedscience.org. Accessed on March 4, 

2016. 

HR.AC. 2015. Herbicide Resistance Management, Proposed HR.AC Stewardship Guidelines for 

Herbicide Labels. Accessed online on September 24, 2015 at 

http://www.hracglobal.com/pages/hracstewardshipguidelinesforherbicidelabels.aspx 

Accessed on March 3, 2016. 

Legleiter, T. R., & Bradley, K. W. (2008). Glyphosate and multiple herbicide resistance in 

common waterhemp (Amaranthus rudis) populations from Missouri. Weed Sci., 56, 582-

587. http://dx.doi.org/1O.l6 l 4/WS-07-204.1 . 

Livingston, M., J. Fernandez-Cornejo, J. Unger, C. Osteen, D. Schimmelpfennig, T. Park, and D. 

Lambert. 2015. The Economics ofGlyphosate Resistance Management in Corn and 

Soybean Production, ERR-184, U.S. Department of Agriculture, Economic Research 

Service, April 2015. 

Market Research Data. 2010-2014. Data collected and sold by a private market research firm. 

Data collected on pesticide use for about 60 crops by annual surveys of agricultural users in 

the continental United States. Survey methodology provides statistically valid results, 

typically at the state level. 

Norsworthy, J.K., S. M. Ward, D. R. Shaw, R. S. Llewellyn, R. L. Nichols, T. M. Webster, K. 

W. Bradley, G. Frisvold, S. B. Powles, N. R. Burgos, W. W. Witt, and M. Barrett. 2012. 

Reducing the Risks of Herbicide Resistance: Best Management Practices and 

Recommendations. Weed Science 2012 Special Issue: 31-62. Available online at: 

http://www.wssajournals.org/doi/pdf/l 0. 1614/WS-D-11 -00155.1 . Accessed on March 

4,2016. 

Ratnayake, S. 2015. Rice Production Practices in the United States and Use of Cyhalofop-butyl for 

Weed Control in Rice Production, Revised (DP# 420989). Publication ofUSEPA. Biological 

and Economic Analysis Division. 

Shaw, D.R., W. H. Morris, Webster, E. P., and D. Smith. 2000. Effects of Spray Volume and 

Droplet Size on Herbicide Deposition and Common Cocklebur Control. Weed Technology, 

Volume 14:321-326. Accessed on March 4, 2016. · 

Texas Rice Production Guidelines. 2014. Texas A& M Agri life Extension. Texas A&M 

University. Onl.ine Publication. Available at: 

http://extentopubs.tamu.edu/pdf/2014 Rice Production Guidelines.pdf. Accessed on 

October 30, 2015. · 

University of Arkansas. 2013. Arkansas Rice Production Handbook. University of Arkansas 

Division of Agriculture. Available at: 

http://www.uaex.edu/publications/pdf/mpl 92/mpl 92.pdf. Accessed on November 11, 

2015. . 

Page 13 
USEPA (United States Environmental Protection Agency). Office of Pesticide Programs. 2004. 

Online Publication. Available at: 

http://www3.epa.gov/pesticides/chem search/reg actions/reregistration/red PC114402 24-Feb-04.pdf Accessed on Nov. 11, 2015. 

Weed Science Society of America. 2014. Herbicide Handbook 10th edition. 

Page 14 
APPENDIX I. Guidance for Pesticide Registrants on Pesticide Resistance Management 

La.beling (EPA, 2001) 

Herbicides 

1. The following general resistance management labeling statements are recommended for 

herbicide products containing only a single active ingredient or only active ingredients 

from the same group: 

a. "For resistance management, (name of product) is a Group (mode of action group 

number) herbicide. Any weed population may contain or develop plants naturally 

resistant to (name of product) and other Group (mode of action group number) 

herbicides. The resistant biotypes may dominate the weed population if these 

herbicides are used repeatedly in the same field. Other resistance mechanisms that are 

not linked to this mode of action but are specific for individual chemicals, such as 

enhanced metabolism, may also exist. Appropriate resistance-management strategies 

should be followed." 

For products containing active ingredients from different groups, the statement should be 

modified to reflect the situation, f~r example: 

b. "For resistance management, please note that (name of product) is both a Group (mode 

of action group number) and a Group (mode of action group number) herbicide. Any 

weed population may contain plants naturally resistant to Group (mode of action group 

number) and/or Group (mode of action group number) herbicides. The resistant 

individuals may dominate the weed population if these herbicides are used repeatedly 

in the same fields." 

2. The following additional resistance management labeling statements are recommended for 

herbicides, although each bulleted statement may not be appropriate or pertinent for every 

product label: 

"To delay herbicide resistance: 

a. Rotate the use of (name of product) or other Group (mode of action group number) 

herbicides within a growing season sequence or among growing seasons with different 

herbicide groups that control the same weeds in a field. 

b. Use tank mixtures with herbicides from a different group if such use is permitted; Use the 

less resistance-prone partner at a rate that will control the target weed(s) equally as well 

as the more resistance-prone partner. 

c. Adopt an integrated weed management program for herbicide use that includes scouting 

and historical information related to herbicide use and crop rotation, and that considers 

tillage (or other mechanical control methods), cultural (e.g., higher crop seeding rates; 

Page 15 
precision fertilizer application method and timing to favor the crop and not the weeds), 

biological (weed-competitive crops or varieties) and other management practices. 

d. Scout after herbicide application to monitor weed populations for early signs of resistance 

development. Indicators of possible herbicide resistance include: (1) failure to control a 

weed species normally controlled by the herbicide at the dose applied, especially if 

control is achieved on adjacent weeds; (2) a spreading patch of non-controlled plants of a 

particular weed species; (3) surviving plants mixed with controlled individuals of the 

same species. If resistance is suspected, prevent weed seed production in the affected 

area by an alternative herbicide from a different group or by a mechanical method such as 

hoeing or tillage. Prevent movement of resistant weed seeds to other fields by cleaning 

harvesting and tillage equipment when moving between fields, and planting clean seed. 

e. If a weed pest population continues to progress after treatment with this product, 

discontinue use of this product, and switch to another herbicide with a different target 

mode of action, if available. 

f. Have suspected resistant weed seeds tested by a qualified laboratory to confirm resistance 

and identify alternative herbicide options. 

g. Contact your local extension specialist or certified crop advisors for additional pesticide 

resistance-management and/or integrated weed-management recommendations for 

specific crops and weed biotypes. 

h. For further information or to report suspected resistance, contact (company 

representatives) at (toll free number) or at (Internet site)." 

APPENDIX II. Definition of Resistance and Likely Resistance 

According to the Weed Science Society of America "Herbicide resistance is the inherited ability 

of a plant to survive and reproduce following exposure to a dose of herbicide normally leth~ to 

the wild type. In a plant, resistance may be naturally occurring or induced by such techniques as 

genetic engineering or selection of variants produced by tissue culture or mutagenesis." 

"Herbicide tolerance is the inherent ability of a species to survive and reproduce after herbicide 

treatment. This implies that there was no selection or genetic manipulation to make the plant 

tolerant; it is naturally tolerant." (http://weedscience.org/documents/resistancecriterion.pdf). 

Indicators of likely herbicide resistance (called possible resistance in Norsworthy et al 2012, 

Page 39) inchide (1) failure to control a weed species normally controlled by the herbicide at the 

dose applied, especially if control is achieved on adjacent weeds; (2) a spreading patch of 

noncontrolled plants of a particular weed species; and (3) surviving plants mixed with controlled 

individuals of the same species. 

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APPENDIX III. Best Management Practices for Herbicide Resistant Weeds 

Crop Selection and Cultural Practices: 

1. Understand the biology of the weeds present. 

2. Use a diversified approach toward weed management focused on preventing weed seed 

production and reducing the number of weed seeds in the soil seed-bank. 

3. Emphasize cultural practices that suppress weeds by using crop competitiveness. 

4. Plant into weed free fields, keep fields as weed free as possible, and note areas where weeds 

were a problem in prior seasons. 

5. Incorporate additional weed control practices whenever possible, such as mechanical 

cultivation, biological management practices, crop rotation, and weed-free crop seeds, as part 

of an integrated weed control program. 

6. Do not allow weed escapes to produce seeds, roots or tubers. 

7. Manage weed seed at harvest and post-harvest to prevent a buildup of the weed seed-bank. 

8. Prevent field-to-field and within-field movement of weed seed or vegetative propagules. 

9. Thoroughly clean plant residues-from equipment before leaving fields. 

10. Prevent an influx of weeds into the field by managing field borders. 

11. Fields should be scouted before application to ensure herbicides and application rates will be 

appropriate for the weed species and weed sizes present. 

12. Fields should be scouted after application to confirm herbicide effectiveness and to detect 

weed escapes. 

13. If resistance is suspected, treat weed escapes with an alternate mode of action or use nonchemical methods to remove escapes. 

14. A void outcrossing to weedy ela~ives, in crops that outcross. Control weedy relatives in 

surrounding field margins. Research has demonstrated that the pollen can move __ feet. 

Herbicide Selection: 

1. Use a broad spectrum soil applied herbicide with a mechanism of action that differs from this 

product as a foundation in a weed control program. 

2. A broad spectrum weed control program should consider all of the weeds present in the field. 

Weeds should be iden~fied through scouting and field history. 

3. Difficult to control weeds may require sequential applications of herbicides with alternative 

mechanisms of action. 

4. Fields with difficult to control weeds should be rotated to crops that allow the use of 

herbicides with alternative mechanisms of action. 

5. Apply full rates of this herbicide for the most difficult to control weed in the field. 

Applications should be made when weeds are at the correct size to minimize weed escapes. 

6. Do not use more than two applications of''this herbicid~'~ or any herbicide with the same 

mechanism of action within a single growing season unless mixed with another mechanism 

of action herbicide with overlapping spectrum for the difficult to control weeds. 

7. Report any incidence of non-performance of this product against a particular weed species to 

the representative (list contact information here). · 

Footnote: Most items are taken from the Herbicide Resistance Action Committee I Weed 

Science Society of America list of Best Management Practices. 

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