### UNITED STATESENVIRONMENTAL PROTECTION AGENCY 

### WASHINGTON D.C., 20460

MAR 10 2016
OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION 

### MEMORANDUM
SUBJECT: 

### Propoxycarbazone: Usage on Wheat and Proposed Herbicide Resistance Management Measures (PC #

### 122019). FROM: 

### Carl Chen, Ph
.D., Biologist 

## GM.J..**~** 

# I'd:-_ William Chism, Ph.D
., Senior Biologist
.

### ~ (') (}. Jonathan Becker, Ph.D., Senior Science Advisor 

# f'---**~ ~** 

TllRU: 

### Biological Analysis Branch 

# flStephen Smearman, Economist**k-.,J,.~~** 

## /
. Economic Analysis Branch

### ~~ Biological and Economic Analysis Division (7503P) Colwell Cook, Ph.D., Acting Chief

# ~- 

# /Jll.. I**~** 

# Colu.et( Gx,J::_ Biological Analysis Branch 

# r j f**~** Economic Analysis Branch 

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### Timothy Kiely, Chief

# ~ \4

# ·~ Biological and Economic Analy · Division (·50 ) TO: 

### Marianne Mannix, Chemical Review Manager Kelly Sherman, Chief Risk Management and Implementation Branch III Pesticide Reevaluation Division (7508P)
BEAD Product Review Panel date: February 24, 2016

1

### SUMMARY The herbicide propoxycarbazone sodium is undergoing registration review in the Office of Pesticide Programs. In this memo, BEAD provides information on use and usage parameters to help characterize the modelled
.ecological risks ofpropoxycarbazone sodium, including the extent ofaerial applications, the number ofmultiple applications, and the application rates commonly used by growers. BEAD also provides information about the risks ofdevelopment of weed resistance to propoxycarbazone sodium and proposes measures for resistance management. The Biological and Economic Analysis Division (BEAD) analyzed Market Research Data to determine the number ofspring and winter wheat acres treated with propoxycarbazone sodiUm. BEAD determined that use ofpropoxycarbazone sodium on wheat is extremely small nationally with approximately 2% ofall wheat acres being treated and that ofthose acres treated with propoxycarbazone sodium, less than 1 % ofall wheat acres are treated aerially
. Most aerial applications are made to winter wheat. Although propoxycarbazone sodium use is relatively low nationally, two states, Oregon and Washington, appear to rely on aerial applications. Oregon and Washington with 27% and 13% oftheir wheat acres treated aerially with propoxycarbazone sodium as a percent oftotal treated acres. On average, the annual application rates are well belowthe label maximum rate. However, for winter wheat, up to three applications may be used with annual rates that are close to the label maximum
. Propoxycarbazone sodium may have some niche uses as being effective against certain primary weed pests. It is one ofthe commonly used cheatgrass herbicides in winter wheat (Market Research Data, 2010-2014). BEAD concurs with the registrant that the recommended droplet size for aerial application is "coarse" based on the limited information that is publically available on the efficaciousness of the product under scenarios where the droplet size is varied. To address the spread ofherbicide 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 ofthe mechanism ofaction, resistant weeds, and weed management strategies) with the least concern for herbicide resistant weeds will have the fewest number ofresistance management elements and the situations with the highest concern will have the most resistance management elements
. In addition to the propoxycarbazone sodium docket, a separate docket is being established for the Agency's herbicide resistant management approach. All stakeholders are encouraged to submit comments to both dockets. Public comments received from both the chemical specific docket will be considered prior to the Agency's final decision onpropoxycarbazone sodium. Propoxycarbazone sodium is an inhibitor ofacetolactate synthase (ALS) and the Weed Science Society ofAmerica (WSSA) has categorized it as mechanism ofaction (MOA) Group 2. This MOA is ofhigh concern for weed resistance development because this mechanisms ofaction has a large number ofconfirmed herbicide resistant weeds species in the U.S., is used on a crop (wheat), which has many reported resistant weeds, and seven ALS herbicide resistant crops have been commercialized (conventionally bred or GM). 2The Agency is proposing here a set ofherbicide resistance elements for propoxycarbazone sodium. This includes changes to the label language and elements on reporting, education and stewardship. Background Propoxycarbazone sodium is now in the decision-making phase ofregistration review. The Agency is considering changes and restrictions in its use to mitigate potential ecological risks as mandated under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), which requires EPA to register pesticides before they can be distributed and used FIFRA Section 3(g) mandates that EPA re-evaluate the registrations at least once every 15 years. This periodic review is necessary in light ofscientific advancements, changes in policy, and changes in use patterns that may alter the conditions underpinning previous registration decisions. FIFRA requires EPA to regulate the use ofa pesticide to the extent necessary to prevent unreasonable adverse effects on the environment, including human health, where 'unreasonable' is defined as taking into account the economic, social, and environmental costs and benefits ofthe use ofthe pesticide. The Agency is considering options for mitigating risks to non-target plants that will be implemented through product label changes. OPP has completed risk assessments for propoxycarbazone sodium, an herbicide that is most commonly used in wheat production, butthat may also be used on fallowed land, pasture and rangeland, and Conservation Reserve land
. OPP's ecological risk assessments have identified risks to non-target plant species in areas adjacent to treated fields. Aerial applications will typically pose the greatest risks since drift is more likely and more widespread. Other main drivers in the risk assessment include application rates, frequency ofapplication, droplet size, and boom height. Propoxycarbazone sodium Propoxycarbazone sodium inhibits acetolactate synthase (ALS), and is classified bythe Weed Science Society ofAmerica (WSSA) as a WSSA Group 2 herbicide (WSSA, 2016). It is a selective herbicide and is absorbed by leaves and roots and then translocated. Propoxycarbazone sodium is characterized by a low rate ofuse and its efficacy is not affected by low air temperatures (Guarnone and Davi, 2012). The major agricultural use ofpropoxycarbazone sodium is in wheat. It is applied postemergence to the weeds through ground or aerial application equipment. It was applied to more than one million acres annually, approximately 2% ofall wheat acres in the United States, with a higher percentage in certain regions such as Washington
. Propoxycarbazone sodium has an efficacy rating of "excellent" for cheatgrass control (TAMU, 2008), and is one ofthe commonly used cheatgrass herbicides in winter wheat (Market Research Data, 2010-2014). Alternatives to propoxycarbazone sodium in winter wheat include other ALS herbicides as well as synthetic auxins (WSSA Group 4). Alternatives for spring wheat are other ALS herbicides, as well as synthetic auxin, and inhibitors ofACCase (WSSA Group 1 ), and photosystem II 3inhibitors (WSSA Group 6). Most ofthese alternatives have been used mainly postemergence, like propoxycarbazone sodium. 

### Usage Forthe years 2010 to 2014, approximately 26,000 lb a.i. ofpropoxycarbazone sodium are applied annually on an average of 1, 100,000 acres. Nationally, approximately 2% ofall wheat acres are treated with propoxycarbazone sodium. About 87% ofthe total pounds of propoxycarbazone sodium is used on winter wheat and the remaining 13% on spring wheat. In terms ofarea treated, about 72% ofthe acres treated are winter wheat and the remaining 28% is on spring wheat. (Table 1 )
. 

### Table 1. 

### Propoxycarbazone sodium PCT, Average Annual Pounds Applied and Average A I' 

### ti R t



### ,pp 1ca on a e. Average Average Average Percent Average Application

Acres Base Acres Crop Annual lbs Rate Crop Grown Treated Treated Applied (lb ai/acre) Spring Wheat 14,575,400 310,922 2.1% 3,236 0.0104 Winter Wheat 38,904,005 792,345 2
.0% 22,135 0.0279 Source: (Market Research Data, 2010-2014) Ofthe 2% ofspring and winter wheat acres treated with propoxycarbazone sodium, approximately 2.5% ofthe spring wheat is treated aerially at an average rate of0.0088 lb a.i. and approximately 5.7% ofthe winter wheat is treated aerially at an average application rate of0.027 lb a.i. (Table 2). 

### T bl 

### 2 P

a e 

# . rooo:x b d' Wh A 

### vcar azone so ium eat cres T

### reatedA
. II P Y er1a 1y er ear. Average Average Average Acres Percent Average lbs Application Total Acres Treated by Treated Applied by Rate Crop Treated Air Aerially Air (lb. ai/acre) Soring Wheat 310,922 7,654 2.5% 67 0
.0088 Winter Wheat 832,773 47,694 5.7% 1,290 0
.0270 Source: (Market Research Data, 2010-2014) Table 3 below presents the maximum single and average application rate as well as the rates used at the 99th percentile and the percentage ofacres that are treated multiple time for spring and winter wheat. The label maximum single application rate for both spring and winter wheat is 0
.039 lbs a.i
. per acre. The average application rate for spring wheat is 0
.010 lbs a.i. per acre and 0
.0279 lbs a.i. per acre for winter wheat. About 99% ofthe acres are treated at a rate of0.0270 and 0.0390 lbs a.i. per acre or lower for spring wheat and winter wheat, respectively. Winter wheat receives multiple applications and that occurs on about 3.4% ofwheat acres that are treated
.


### 4

### T 

### bl 3 M If I A I' 

### a e 

# . U IP 

### e • DD 

### 1cations of 

### P b d" 

### ropoxycar azone so 1um by Crop
. *Labelled Average Application Rate Crop Maximum Single for 99 Percentile of Annlication Rate Application Rate Acres Treated Sprin2 Wheat 0.0394 0.0104 < 0.0270 lbs/acre Winter Wheat 0.0394 0.0279 < 0
.0390 lbs/acre Source: (Market Research Data, 2010-2014) Numbers have been rounded. *EPA, EFED Label Data Report, 2014 % ofAcres Treated Multiple Times

0% 3.4%

Table 4 shows the aerial treatments at the state level for states that reported propoxycarbazone sodium use on wheat. At the state level, the states with the highest percent oftheir wheat acres treated aerially with propoxycarbazone sodium as a percent ofthe total acres treated are Oregon (27%) and Washington (13%). 

### Table 4. Average Wheat Acres Grown and the Percent ofTotal Wheat Acres Treated with P b d 0 A 

## r d A . II



### ropoxvcar azone so IUm •PP 

### 1e er1a 1y. State Average Wheat Acres Percent ofTotal StateWheat Acres Treated Grown* Aerially with Propoxvcarbazone sodium Oregon 812,222 27% Washington 2,191 , 111 13% South Dakota 2,411,002 8% N. Dakota 7,004,446 2% Oklahoma 5,611,107 1% Source: (Market Research Data, 2005-2013) *Includes both winter and spring wheat acres based on Market Research Data
. 

### Number ofApplications Table 5 below illustrates the number ofspring and winter wheat acres that are treated once and the number ofacres that are treated more than once. According Market Research Data for the years 2010 to 2014, 100% ofthe spring wheat was treated only once. Forthe same time period, 94
.5% ofwinter wheat was treated only once. However, Market Research Datareports that winter wheat had up to 3 applications. Approximately 6% ofthe winter wheat acres were treated twice and about 0.5% ofthe winter wheat acres had up to 3 applications. T bl 5 N b



### a e 

# . um fWh tA ero ea cres 

### T t 

### dM If I T" rea e u 1p1e 1mes SpringWheat WinterWheat Acres Treated 310,922 792,345 Acres Treated Once 310,922 765 ,705 Lbs Aoolied 3,236 20,744 A

vera2e AnoIi cation Rate (lbs ail acre 0
.0104 0.0271 Sprine: 

### Wheat Winter Wheat Acres Treated Multiple Times 0 26,640 Lbs Aoolied 0 1,391 Average Application Rate Obs ail acre) NIA 0.0522 Source: Market Research Data (2010-2014)

5

### SPRAY DRIFT MITIGATION Several variables affect the magnitude and distance ofdrift during aerial application. These include: droplet size; speed; boom width; elevation ofaircraft during application; nozzle size; optimal environmental conditions and chemical formulation, among several others. Several publications describe these, and other, variables in more detail and provide best management practices for spray drift (ASABE, 2012; O'Connor-Marer, 2011, and VT, 2015). Based on recent conversations with the registrant ofpropoxycarbazone sodium, the droplet size that they recommend for aerial application is "coarse". BEAD concurs with the registrant based on the limited information that is publically available on the efficaciousness ofthe product under scenarios where the drop size is varied. 

### RESISTANCE MANAGEMENT The development and spread ofherbicide resistant weeds in agriculture is a widespread problem that has the potential to fundamentally change production practices in US agriculture. While herbicide resistance weeds have been known since the 1950s, the number ofspecies and their geographical extent, has been increasing rapidly. Currently there are 249 weed species worldwide with confirmed herbicide resistance, especially since the turn ofthe century. In the United States there are 155 weed species with confirmed resistance to one or more herbicides. Management ofherbicide resistant weeds, both in mitigating established herbicide resistant weeds, and in slowing or preventing the development ofnewherbicide resistant weeds is a complex problem without a simple solution. Coordinated efforts ofgrowers, agricultural extension, academic researcher, scientific societies, pesticide registrants, and state and federal agencies are required to address this problem. In September 2014, the Weed Science Society ofAmerica sponsored an international meeting, the Herbicide Resistance Summit II, hosted by the National Research Council (WSSA, 2014). This meeting was organized to facilitate a more unified understanding ofthe herbicide resistance issues across the country, understanding ofdifferences ofviewpoints, 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 ofthis 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 ofAgriculture announced USDA's herbicide resistance actions that were developed in collaboration with the Environmental Protection Agency (USDA, 2014). The EPA, Office ofPesticide 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 ofherbicide resistant weeds. This is part ofa more holistic, proactive 

### 6approach recommended by crop consultants, commodity organizations, professional/scientific societies, researchers, and the registrants themselves. OPP's approach is measured, based on the inherent risk ofweed resistance developing for a given herbicide, considering the target weeds and the agronomic practices ofthe registered crops. Situations with the least concern for the development ofherbicide 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 Pesticide Registrants on Pesticide Resistance Management Labeling (EPA, 2001) • Appendix II - Definition ofResistance and Likely Resistance • Appendix III- Best Management Practices for Herbicide Resistant Weeds (from the Herbicide Resistance Action Committee and the Weed Science Society ofAmerica Implementation Timeline and Opportunities for Public Comment on Herbicide Resistance Approach OPP is proposing to implement herbicide resistance measures for existing chemicals during registration review, and to implement herbicide resistance measures for newchemicals and uses at the time ofregistration. In registration review, proposed herbicide resistance elements will in every herbicide preliminary interim decision. Comments onthese chemical specific measures are welcomed. All stakeholders are encouraged to comment on the herbicide resistance management approach, rationale, and proposed elements. Public comments received from both the chemical specific docket and the separate HR management docket will be considered prior to the final decision on this propoxycarbazone sodium. Propoxycarbazone sodium Specific Herbicide Resistance Measures Propoxycarbazone sodium acts to inhibit acetolactate synthase (ALS), a key enzyme in the biosynthesis ofthe branched-chain amino acids in plants. This herbicide is classified by the Weed Science Society ofAmerica (WSSA) as belonging to WSSA Mechanism ofAction (MOA) Group 2 (WSSA, 2016). This MOA has a number ofconfirmed resistant weeds with over 150 confirmed cases ofweed resistance worldwide and 48 cases ofresistant weed species in the U.S
. Ofthe 48 confirmed ALS resistant weeds in the US, approximately 15 have been identified and reported in wheat. Several target weeds in wheat have confirmed resistance to propoxycarbazone sodium. This MOA is ofthe highest concern for weed resistance development because this mechanism of action already has a large number ofconfirmed herbicide resistant weeds species in the U.S., is used on large acreage crop, wheat, with many reported resistant weeds, and Group 2 has seven commercialized herbicide resistant crops. Table 6 describes the elements ofa resistance


### 7management and stewardship plan
. Table 7 identifies the elements needed for each level of concern. Table 6. Elements ofa resistance management and stewardship plan



### Element Description List Mechanism ofAction (MOA) Group Number
. 1 

# • This information is critical to allow the user to rotate between effective MOA's to reduce the buildup ofresistantpests. )- Registrant is responsible for placement on label. List seasonal and annual maximum number ofapplications and amounts. 

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

### 2 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 

### 3 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 4 applied based on the weed species and growth stage and determine ifthe pesticide applied provided effective control. )- Registrant is responsible for placement on label. )- User is responsible for following the recommendations. Definition ofLikely Resistance. 

# • It can take up to five years to confirm herbicide resistance. By describing 5 likely resistance users could proactively identify and attempt to control weeds in the early stages before they become widespread in their fields. )- Registrant is responsible for placement on label. User should report lack ofperformance to registrant ortheirrepresentative. 

## • Reporting lack ofperformance can help provide the user with additional resources for the identification and control ofproblem weeds. In some 

### 6 cases lack ofperformance could be an early indication oflikely 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. 7 

## • 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. 

### 8)oi- Registrant is responsible for placement on label. Registrant report new cases oflikely 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 8 available in a timely manner to users, consultants, extension, etc. so that they are aware ofand proactively address the problem. 

# • Provide weed species, crop or site, state, and herbicide used
. )oi- Registrant is responsible for reporting. For sites ofhigh concern provide growers with:

D Resistance Management Plan 0 Remedial Action Plan (to control resistant weeds this season ornext 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 ofthe importance of resistance management. )oi- 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 ofresistance. 

# • The elements may be on the label, the technical use agreement for the seed trait, or as a reporting requirement. )oi- Registrant is responsible. 

### Footnote: Mechanism ofAction Group number comes from the WSSA, definition ofresistance and likely resistance, PRNotice 2001-5 and BMP language are in Appendix 1-3
. Resistance elements for fungicides and insecticides
.



### 9Table 7
. Herbicide Resistance Categories ofConcern
Low Concern Moderate Concern High Concern • Any new herbicide with a new or

novel mechanism ofaction, or MOA' s with no MOA's with a few resistant • Herbicide resistant crop(s) for resistance weed weed species in the U.S
. that technology (conventionally species in the U.S. bred or GM), or • MOA's with highest number of

resistant weeds in U.S. 1. MOA on Label Elements 1 through 4 plus Elements 1through 8 plus 2
. List seasonal and 5
. Definition oflikely and 9
. Provide growers with: annual maximum confirmed resistance Resistance Management Plan, number of 

### 6
. Farmer should report Remedial Action Plan, applications and lack ofperformance to Educational materials on pounds registrant or its agent resistance management 

### 3
. Resistance 7
. List confirmed resistant 10
. Forcombination products with management species in separate multiple MOAs, list which language from table and list effective herbicide is controlling which PRN 2001-5 or or recommended rates weed and minimum BMPs for these weeds with recommended rate 4. Scout before and the table 11. Any additional specific after application 

### 8
. Registrant report new requirements (e
.g. mandatory cases oflikely and crop rota tion, unique agronomic confirmed resistance to aspects, time limited EPA 

### & users yearly registration, etc.)
. 

## * Ifnew resistant weed species are found a MOA may move to higher level ofconcern.


### REFERENCES ASABE. 2012
. Best Management Practices for Boom Spraying. Approved January 2007 ; reaffirmed March 2012 as an American National Standard. American Society of Agricultural and Biological Engineers (ASABE)
. Environmental Protection Agency
. BEAD Chemical Profile (BCP) for Registration Review: Propoxycarbazone sodium (122019) 2014
. EPA. 200I
. Pesticide Registration (PR) Notice 2001-5
. Guidance for Pesticide Registrants on Pesticide Resistance Management Labeling. Accessed February 2016 at http:// www.epa.gov/pesticide-registration/prn-2001-5-guidance-pesticide-registrantspesticide-resistance
-management.

IOGuamone A, Davi R. 2012. Propoxycarbazone-sodium: newpost-emergence herbicide for soft and durum wheat. Accessed February 2016 at http://www
.cabdirect.org/abstracts/20143039835
.html;jsessionid=4ACl 6B48BE96B7367 8lEl4841F2D992B:jsessionid=B49EAC3672A5F442FOF04C95CB650BFC. Housenger, 

### J. 2014. USDA Stakeholder Workshop on Coexistence March 12, 2015. Accessed March 2016 at: https:// www.aphis.usda.gov/stakeholders/downloads/2015/coexistence /JackHousenger.pdf HRAC
. 2016. Classification ofHerbicides According to Site ofAction
. Herbicide Resistance Action Committee (HRAC)
. Accessed February 2016 at http://hracglobal
.com/pages/classificationofherbicidesiteofaction.aspx Heap I. 2016. The International Survey ofHerbicide Resistant Weeds
. Accessed February 2016 at http://www.weedscience.org/summary/ResistbyActive.aspx. Market Research Data (MRD) (1998

- 2014). Datacollected and sold by a private market research firm
. Datacollected 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 JK, Ward SM, Shaw DR, Llewellyn RS, Nichols RL, Webster TM, Bradley KW, Frisvold G, Powles SB, Burgos NR, Witt WW, Barrett M. 2012. Reducing the risks of herbicide resistance: Best Managment Practices and Recommendations
. Weed Science Special Issue: 31-62. Accessed February 2016 at http://wssajournals
.org/doi/pdf/1O.l614/WS-D-11-00155.1 O'Connor-Marer, P. J. 2011. Aerial Applicator's Manual. A National Pesticide Applicator Certification Guide. National Assoeiation ofState Departments ofAgriculture Research Foundation. Accessed on March 7, 2016 at http://www.nasda.org/File
.aspx?id=3786 TAMU, 2008. Weed Control Recommendations in Wheat. Texas A&M University (TAMU) Extension
. Accessed February 2016 athttp://amarillo.tamu.edu/files/2010/ll/B-6139- 2008-Weed-Control.pdf
. USDA, 2014. USDA Announces Measures to Help Farmers Diversify Weed Control Efforts
. United States Department ofAgriculture
. Accessed March 2016 at: www.usda.gov /wps/portal/usda/usdamediatb?contentid=2014/10/0227.xml&printable=tr ue&contentidonly=true
. VT
. 2015
. Nozzles: Selection and Sizing
. Virginia Cooperative Extension Publication 442-032
. Virginia Tech
. Accessed November 2015 at https://pubs.ext.vt.edu/442/442-032/442- 032 pdf.pdf
. WSSA. 2014. Herbicide Resistance Summit II
. Weed Science Society ofAmerica
. Accessed March 2016 at http://wssa
.net/wssa/weed/resistance-summit-ii/. 11WSSA
. 2016
. Classification ofHerbicides According to Site ofAction
. Weed Science Society of America
. Accessed February 2016 at http://weedscience.org/documents/showdocuments.aspx?DocumentID=1193.

12APPENDIX I. Guidance for Pesticide Registrants on Pesticide Resistance Management Labeling (EPA, 200I) 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. "Forresistance management, (name ofproduct) is a Group (mode ofaction group number) herbicide
. Any weed population may contain or develop plants naturally resistant to (name ofproduct) and other Group (mode ofaction group number) herbicides. The resistant biotypes may dominate the weed population ifthese herbicides are used repeatedly in the same field
. Otherresistance mechanisms that are not linked to this mode ofaction 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, for example: b
. "For resistance management, please note that (name ofproduct) is both a Group (mode ofaction group number) and a Group (mode ofaction group number) herbicide. Any weed population may contain plants naturally resistant to Group (mode ofaction group number) and/or Group (mode ofaction group number) herbicides. The resistant individuals may dominate the weed population ifthese 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 ofproduct) or other Group (mode ofaction 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 ifsuch 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;
13precision 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 ofresistance development. Indicators ofpossible herbicide resistance include: (1) failure to control a weed species normally controlled by the herbicide at the dose 

### applied, especiallyif control is achieved on adjacent 

### weeds; (2) a spreading patchofnon-controlled plants ofa particular weed species; (3) surviving plants mixed with controlled individuals ofthe same species. 

### Ifresistance is suspected, prevent weed seed production in the affected area by an alternative herbicide from a different group orby a mechanical method such as hoeing or tillage
. Prevent movement ofresistant weed seeds to other fields by cleaning harvesting and tillage equipment when moving between fields, and planting clean seed
. e. 

### Ifa weed pest population continues to progress after treatment with this product, discontinue use ofthis product, and switch to another herbicide with a different target mode ofaction, ifavailable
. 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)
."

14APPENDIX II. Definition ofResistance and Likely Resistance According to the Weed Science Society ofAmerica " Herbicide resistance is the inherited ability ofa plant to survive and reproduce following exposure to a dose ofherbicide normally lethal to the wild type. Jn a plant, resistance may be naturally occurring or induced by such techniques as genetic engineering or selection ofvariants produced by tissue culture or mutagenesis." "Herbicide tolerance is the inherent ability ofa 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 oflikely herbicide resistance (called possible resistance in Norsworthy et al 2012, Page 39) include (1) failure to control a weed species normally controlled by the herbicide at the dose applied, especially ifcontrol is achieved on adjacent weeds; (2) a spreading patch of noncontrolled plants ofa particular weed species; and (3) surviving plants mixed with controlled individuals ofthe same species
.



### 15APPENDIX 111
. Best Management Practices for Herbicide Resistant Weeds (from the Herbicide Resistance Action Committee I Weed Science Society ofAmerica list ofBest Management Practices) Crop Selection and Cultural Practices: 1. Understand the biology ofthe weeds present. 2
. Use a diversified approach toward weed management focused onpreventing weed seed production and reducing the number ofweed 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 ofan 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 ofthe weed seed-bank. 8
. Prevent field-to-field and within-field movement ofweed seed orvegetative propagules. 9. Thoroughly clean plant residues from equipment before leaving fields
. 10
. Prevent an influx ofweeds 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. 

### Ifresistance is suspected, treat weed escapes with an alternate mode ofaction or use nonchemical methods to remove escapes. 14. Avoid outcrossing to weedy relatives, 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 ofaction that differs from this product as a foundation in a weed control program. 2
. A broad spectrum weed control program should consider all ofthe weeds present in the field. Weeds should be identified through scouting and field history
. 3. Difficult to control weeds may require sequential applications ofherbicides with alternative mechanisms ofaction
. 4. Fields with difficult to control weeds should be rotated to crops that allow the use of herbicides with alternative mechanisms ofaction. 5
. Apply full rates ofthis 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 herbicide" or any herbicide with the same mechanism ofaction within a single growing season unless mixed with another mechanism ofaction herbicide with overlapping spectrum for the difficult to control weeds. 7. Report any incidence ofnon-performance ofthis product against a particular weed species to the representative (list contact information here).

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