UNITED STATES ENVIRONMENT AL PROTECTION AGENCY 

WASHING TON D.C., 20460 

FEB 2 9 2016 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

MEMORANDUM 

SUBJECT: 

FROM: 

THRU: 

TO: 

Bentazon Usage Information (PC# 103901) 

Caleb Hawkins, Environmental Protection Specialist // ~ 

Biological Analysis Branch {Jc.~ 1 {~ ~ 

Rafael Prieto, Environmental Protection Specialist /J~A / /" /) ~ f 

Science Information Analysis Branch , 1/ "--L V\. _.r ('lA/llrZi. 

Elizabeth Hill, Economist C:::::. _ Economic Analysis Branch ~:__----::;;; ...... .....__..........,,.-- Biological and Economic Analysis-Division (7503P) 

Colwell Cook, Acting Chief ~J( tJBiological Analysis Branch 

Timothy 

Economic Kiely, Analysis 

Chief 

Branch QJ \f'\. ~ Biological and Economic Analysi ivision C 503 

Moana Appleyard, Chemical Review Manager 

Linda Arrington, Chief 

Risk Management and Implementation Branch V 

Pesticide Reevaluation Division (7505P) 

BEAD Product Review Panel date: December 16, 2015 
SUMMARY 

This document describes the use and usage of bentazon (also referred to as sodium bentazon), 

which is undergoing registration review in the Office of Pesticide Programs (OPP). The 

Biological and Economic Analysis Division (BEAD) is providing information on the use and 

benefits of bentazon as part of the risk-benefit process which informs the decision phase of 

registration review. This memo describes key crops where bentazon is used, typical treatment 

rates, application timing and intervals, information on water holding times for rice, and crops 

where applications are made by air. This information will be useful in characterizing the risk 

assessment for bentazon, aiding in the risk management decision, and in informing any risk 

mitigation measures that are found to be necessary. The primary mitigation measure proposed 

by OPP that could impact growers is to limit the number of applications to one per year across all 

crops. Typically, no more than one application is made annually, although multiple applications 

do occur in some limited instances for dry beans/pea, sweet corn, and soybeans. Based on usage 

data and extension documents, BEAD finds that limiting the number of applications could 

potentially limit growers' options for problematic weed control and resistance management. 

To slow the spread of herbicide resistant weeds the Agency is requiring weed resistance to be 

addressed during the registration review process. This is a tiered approach where the situations 

with the least concern for herbicide resistant weeds (fewest number of herbicide resistant weed 

species) will have to address the fewest resistance elements l}lld the situations with the highest 

concern (highest number of herbicide resistant weed species) will have to address the most 

resistance management elements. As the concern for resistance increases more extensive 

resistance components will be required from the registrant. Bentazon is an inhibitor of 

photosynthesis at photosystem II site B (Group 6). Bentazon is of moderate concern for 

resistance because there is at least one weed species resistant to this Mechanism of Action 

(MOA) found in the U.S. and there are no bentazon resistant crops grown in the U.S. 

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. OPP has completed risk assessments 

for bentazon and is considering the risks and benefits to determine if changes to the use 

directions should be made. 

Bentazon is a selective, contact, early post-emergent herbicide registered to control broadleaf 

weeds and sedges in numerous agricultural field crops and around trees and vines in various fruit 

and nut crops. Bentazon is also registered for use to control weeds in residential and recreational 

lawns around ornamental plants. Bentazon is a salt which rapidly dissolves in water to produce a 

sodium ion and a bentazon acid anion; it is always applied as a spray. 

2 
The Reregistration Eligibility Decision document (RED) for bentazon was issued in 1994. In 

2000, EPA reassessed tolerances ofbentazon in compliance with the Food Quality Protection 

Act (FQPA). EPA published draft human health and ecological risk assessments in 2014. For 

the human health assessment, no data deficiencies were identified in either the toxicity or 

exposure databases and the Agency concluded that bentazon does not pose human health risks. 

The most recent ecological risk assessment concluded that risks to listed and non-listed terrestrial 

plants in uplands and semi-aquatic habitats were of concern to the Agency as well as acute risks 

for small to medium birds that consume plants or small insects, and small mammals that feed on 

short grass (listed species only). The Agency is considering modifications in the use of bentazon, 

such as reductions in the number of annual applications, reductions in application rates, and 

limiting aerial applications, to reduce potential exposure of bentazon to terrestrial plants and 

mammals. 

PURPOSE 

BEAD is assisting in the registration review decision by providing information to help 

characterize the risks and benefits ofbentazon, and possible impacts of mitigation. Possible 

impacts from increasing droplet size and reducing the number of applications may include yield 

loss and the encouragement of herbicide resistance in certain problematic weed species. This 

memo provides information on application rates, application frequency, rice production 

practices, and herbicide resistance management. 

USAGE & APPLICATION TIMING 

Information on usage is presented in Table 1. Bentazon is applied to approximately 1.9 million 

acres of cropland annually in the United States. The crops that are most dependent on bentazon 

in terms of percent crop treated (PCT) include dry beans/peas (42% PCT), peas (33% PCT), bush 

beans (31 % PCT), and peanuts (29% PCT). The maximum seasonal rate across all crops is 2 lbs 

ai/A while the maximum single application rate ranges from 1to1.5 lbs ai/A. Maximum single 

application rates are not typically applied. Market research data (MRD) from 2009 to 2013 

indicates that the average application rate for specific crops ranges from 0.35 to 0.73 lbs ai/A 

(Table 1). 

3 
Table 1. Bentazon: Average versus Maximum Number of Applications and Application 

Rates and Rate Distributions, 2009-2013 Avera ::::;;;:r:~'::;:".":'-:-;-,-~....,..~'='="'."""':-:":':":"'"~"'"'.'""T"'."""7'"-:-"-=--~-,-.,.,--==:-::-:~~ 

256 31% 1.5 0.571 

Com 91 ,499 <1% 1.5 0.614 0.75 

Dry 2,727 42% I.I 1.5 0.528 Beans/Peas 

Lima Beans 36 16% 1.5 0.927 

Peanuts 1, 183 29% 1.5 0.438 0.75 

Peas 

(Fresh/ 178 33% 1.5 0.732 Green/ 

Sweet 

Rice 2,917 1% 0.500 0.75 

Sorghum 6,458 < 1% 0.349 0.5 Milo 

Soybeans 76,824 < 1% I.I 1.5 0.480 0.75 

Sweet Com 559 4% 1.04 1.5 0.723 

MRD, 2009-2013. Numbers have been rounded. 

l Ninety percent or more of all application treatments were at the specified rate or lower for each crop 

listed. BEAD does not have information on the average number of applications for all crops. This table 

does not include all of the crops for which bentazon is registered. 

Bentazon Aerial Usage 

Table 2 provides information on aerial applications for bentazon. Most aerial applications of 

bentazon are made on rice (26,400 total acres treated annually), or 0.9% of the average number 

of crop acres grown annu~ly from 2009-2013. Aerial applications are also made to dry 

beans/peas, with 8,200 total acres treated annually, which equates to 0.3% of the average number 

of total crop acres grown annually from 2009-2013 (Market Survey Data, 2009-2013). Less than 

one percent of bentazon applied to dry beans/peas were made aerially. In contrast, the vast 

majority ofbentazon applications to rice were made by air, with over 74% of bentazon 

applications made aerially. For both dry beans/peas and rice, aerial application rates were 

slightly higher than the rates used for ground applications of bentazon, but were still well below 

the label max rate (the rate used for the risk assessments). 

4 
Table 2. Bentazon: National Aerial Applications, Tot.al Area Treated (acres), Percent Crop 

T reated,-and Application Rate Ob. a.i./acre), 2009-2013 Average. 

Total Area Average Aerial Percent of Total 

Crop Treated Aerially1 Application Rate Area Treated that 

(acres) (lb/A) is made Aerially2 

Dry Beans/Peas 8,200 0.533 <1% 

Rice 26,400 0.689 74% 

MRD, 2009-2013. Numbers have been rounded. 

I Total area treated represents the summation of acres treated by a particular chemical, even those acres that have 

received multiple applications. 

2 This column represents all aerial applications made across total acres treated,'even those acres that received 

multiple applications. This percentage has the potential to slightly differ in comparison to the percentage of base 

acres treated (i.e., acres treated without regard to the number of applications that occurred) with bentazon; typically 

only one application ofbentazon is made annually to dry beans/peas and rice, making total acres and base acres 

treated- and thus the percent of total and base acres treated aerially-similar. 

Multiple Applications of Bentazon 

Typically, no more than one application is made annually, although multiple applications do 

occur in some limited instances for dry beans/peas, sweet com, and soybeans (Table 1). 

For dry beans, approximately 150,000 acres (13% of acres treated with bentazon) in the United 

States receive two applications, while a small percentage of acres have been treated three times. 

Typically the use of second applications are sporadic from year to year, with the exception of 

Michigan and Minnesota where third applications occur regularly on dry beans, accounting for 

7% and 15% of base acres treated annually from 2009 to 2013 (Table 3). 

For soybeans, usage is sporadic across years for all states in which bentazon usage was reported, 

with most of the soybean acres treated with bentazon in Mississippi receiving two applications 

(96% of base acres treated with bentazon); however, these second applications-and usage of 

bentazon overall-is mostly limited to a single year. This may be the result of a problematic pest 

occuring during that time period. Overall, 22% of bentazon base acres treated recevied a second 

application in the United States (34,908 acres). 

T a e bl 3 M . u 1. tip 1 e A .pp I' 1cataons o f B entazon b •Y s tate, 2009 to 2013 A vera2e. 

Dry Beans 

Percent of 

Bentazon 

Treated Acres 

Base Acres Acres Treated Acres Treated Three Treated More 

State Treated Twice Times than Once 

Idaho 25,383 53 1 0 2% 

Michigan 110,414 7,21 I 0 7% 

Minnesota I 17,434 17,310 451 15% 

Montana 11 ,271 119 0 1% 

Nebraska 72,811 821 0 1% 

New York 6,064 64 0 1% 

5 
Dry Beans 

Percent of 

Bentazon 

Treated Acres 

Base Acres Acres Treated Acres Treated Three Treated More 

State Treated Twice Times than Once 

North 

Dakota 745,334 123,027 17% 

United 

States 1, 144,417 149,083 451 13% 

Sovbeans 

Arkansas 51 ,277 1, 184 0 2% 

Mississiooi 31,821 30,537 0 96% 

North 

Dakota 26,860 3,187 0 12% 

United 

States 157,885 34,908 0 22% 

MRD, 2009-2013. Multiple applications have also historically occurred on sweet com, but detailed 

infonnation on multiple applications is unavailable from MRD (2009-2013). This table provides national 

base acres treated and a list the total acres treated twice. The only states listed in the table are states for 

which BEAD has data on multiple applications. 

Any mitigation limiting the number of applications to one per season could negatively impact 

yield and herbicide resistance management in a number of crops. BEAD's data on multiple 

applications are limited and may not capture all instances of multiple applications to control 

problematic weeds. Extension documents identify sequential, lower rate applications in a 

number of crops and for specific problematic weeds (Table 4). 

Table 4: Lists of crops and target weeds where multiple applications of bentazon are 

su22ested by university ae:ricultural extension documents.* 

Crops Weeds 

Corn Kochia 

Sorghum Lambsquaters 

Pulses (lentils, soybeans, beans, pea, peanut, Redroot Pigweed 

etc.) Wild buckwheat 

Yell ow Nutsedge 

Canada thistle 

*This list is not exhaustive. Compiled from Iowa State University Extension, South Dakota State 

University Extension, University of Georgia Extension, Penn State University Extension. 

North Dakota State University Extension states that bentazon is more effective against kochia, 

lambsquarters, redroot pigweed, and wild buckwheat in dry beans when the chemical is applied 

in split treatments at lower concentrations, rather than a single application at the labeled rate 

(Zollinger et al., 2016). Furthermore, Zollinger et al. (2016) recommends up to 4 sequential 

applications for greater control of problematic broadleafweeds in soybeans. Split treatments (7-

10 days apart) ofbentazon are also recommended for control of yellow nutsedge in soybean and 

corn (Penn State, University, 2009). There are likely other crops where bentazon is used in 

6 
lower concentration, split treatments for particular weeds. Multiple applications of bentazon 

may be needed to control particularly resilient weeds species and multiple germination events. 

Furthermore, limiting growers to one application for problematic weeds may encourage 

herbicide resistance. 

Herbicide Resistance Management 

l'he EPA, Office of Pesticide Programs' (OPP), goal is to extend the useful life of chemicals 

used for pest control by slowing the development of resistance. The Agency announced at the 

Herbicide Resistance Summit II sponsored by the National Academy of Sciences (September I 0, 

2014), that it would take a more proactive role in developing regulatory approaches for 

managing resistant weeds. The Summit 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. 

Bentazon, Group 6, inhibits photosynthesis at photosystem II site B. Bentazon is considered of 

moderate concern for herbicide resistance because there is at least one Group 6 MOA resistant 

weeds species found in the U.S. and there are no bentazon resistant crops grown in the U.S. 

Therefore the registrant(s) should address elements 1 through 8 in Table 5. Table 5 lists the 

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

resistant weeds and Table 6 indicates which elements should be addressed based on mechanism 

of action (MOA) and use on herbicide resistant crops. Nine of the eleven items will be 

instructions placed on the label to provide information to the user (elements I through 7, I 0 and 

11 where applicable), and three of the elements will be instructions to the registrant (elements 8, 

9, and 11 where applicable). More information on herbicide resistance management is located in 

appendices I-III. 

Table 5. Elements of resistance mana Ian 

Element 

List Mechanism of Action (MOA) Group Number. 

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

MOk's to reduce the buildup ofresistant pests. 

);;> Re istrant is res onsible for lacement on label. 

List seasonal and annual maximum number of applications 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. 

);:>- Re istrant is res onsible for lacement 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. 

»- Re istrant is res onsible for lacement on label. 

7 
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 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 

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 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 

6 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. 

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. 

);> 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 

8 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 . 

);> Registrant 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 

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

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

8 
• Using a combination products with only one effective MOA can select for 

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. 

~ Registrant 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. 

T a bl e 6 H . er b' 1c1 .d e R es1s. c f C * tance ate2or1es o oncern 

Low Concern Moderate Concern High Concern 

• Any new herbicide with a new or 

novel mechanism of action, 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 most resistant weeds 

in U.S. 

1. MOA on Label Elements I through 4 plus Elements I through 8) plus 

2. List seasonal and 5. Definition of likely and 9. Provide growers with: 

annual maximum confirmed resistance Resistance Management Plan, 

number of 6. Farmer should report Remedial Action Plan, 

applications and lack of performance to Educational materials on 

pounds registrant or its agent resistance management 

3. Resistance 7. List confirmed resistant 10. For combination 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 of likely and crop rotation, unique agronomic 

confirmed resistance to aspects, time limited 

EPA & users yearly registration, etc.). 

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

9 
Bentazon is at moderate risk of resistance for weed species in the U.S., as there is at least one 

case of herbicide resistance to this MOA in the United States (Heap, 2016). Regarding 

resistance to bentazon specifically, there are confirmed cases in Canada (Amaranthus species) 

and in Brazil (Sagittaria montevidensis), but no cases are documented in the United States 

(Heap, 2015). Considering that redroot pigweed (Amaranthus retrojlexus) has already developed 

resistance in Canada, and that university extension documents recommend split applications for 

controlling this species in dry beans, it is important not to limit the number of applications of 

bentazon in certain crops or situations where redroot pigweed, kochia, or lambsquarters is the 

target pest. Reducing the number of applications to only one per season could negatively impact 

grower options. 

Rice 

Water holding time 

Market research data indicate that bentazon is applied early postemergence-preflood and late 

postemergence pre-flood and post-flood. Bentazon is used in drill-seeded rice culture and 

continuous flood cultures, and the chemical is applied to dry fields and flooded fields after rice 

has emerged. This herbicide must come into direct contact with plants; therefore, continuous 

flooded rice culture fields are sometimes partially drained in order to expose weeds to treatment. 

This application would likely occur while weeds are immature and the rice is tillering (several 

weeks before the draining of the field and subsequent harvest). 

Weed control typically begins within days of flooding and continues until the canopy closes and 

weeds can no longer proliferate. Partial to full canopy closure can be expected in the final 

maturation stage (85-115 days after planting), at which point the rice will begin to flower and 

ripen until harvest 130-165 days after planting (University of California, Davis, 1998). Water is 

typically drained 2-3 weeks prior to harvest to allow the field to dry enough to support harvest 

machinery. Considering that the underlying herbicide strategy for weed control is to kill weeds 

or stunt weed growth so that rice can gain a competitive height advantage (University of Florida, 

2015), applications of bentazon will likely occur early to midseason (30-50 days pre-harvest). 

Label changes that would result in growers holding water in the fields for several days after 

bentazon application would likely have little impact on current management practices and weed 

control. In addition, any mitigation measures should avoid having growers drain and apply 

bentazon contemporaneously. Additional information on rice production practices can be found 

in U.S. EPA (2015). 

Herbicide Resistant Management Concerns in Rice 

Bentazon is a management tool used in rice to control ALS-resistant weeds. For example, the 

most problematic weeds in Arkansas rice include banyardgrass, red rice, and sedges (Cyperus 

spp.) (Tehranchian et al., 2015). Mixing bentazon with propanil may limit the spread of ALSresistant sedges in rice fields as this mixture provides >96% control of ALS-resistant smallflower 

umbrella sedge (Norsworthy, 2013). Sagittaria montevidensis (California arrowhead) is a 

IO 
common weed species in rice production in the U.S. and there is confirmed resistance to 

bentazon in Brazil (Heap, 2015). 

Droplet Size and Efficacy of Bentazon 

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 plant 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 the interaction of the active ingredient with other chemicals 

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

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

bentazon. 

A study by Prokopf and Veverka (2003) concluded that "good coverage provided by fine droplet 

spectra is a prerequisite of high efficiency of the contact compound bentazon." Propkof and 

Veverka evaluated the efficacy ofbentazon using Galium aparine (stickywilly) and 

Chenopodium album (lambsquarters) using droplet spectra that ranged from 189 μm to 911 μm 

(fine to ultra course droplet size)1

• The efficiency of Basagran 600 (600 g a.i./l) to control 

stickywilly dropped below 90% at 586 μman~ below 75% at 911 μm (ultra course). Control of 

lambsquarters dropped below 90% at 586 μm and below 61 % at 911 μm. Control efficiency was 

highest (>95%) when droplet size was 183 μm (fine). Based on this study, there was no 

significant difference in efficacy for droplet sizes that ranged from 193 μm (fine) to 484 μm 

(very coarse), and droplets within this range would likely have similar control. 

The American Society of Agricultural & Biological Engineers (ASABE) droplet volume median 

diameter (VMD) classification system differs slightly from the classifications used by Prokopf 

and Veverka. Coarse droplets, as defined by ASABE, range from 326 μm to 400 μm (Grisso and 

Hipkins, 2014). Based on Prokopf and Veverka's study, a label recommendation that limits 

droplet size in the ASABE coarse VMD range (326 μm to 400 μm) would likely not affect the 

efficacy of bentazon for ground applications. 

1 American Society of Agricultural & Biological Engineers Standard 

11 
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Basagran® Herbicide Product Label. Registration No. 7969-45-66330. Online Publication. 

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Owen, M. 2015. Iowa State University Extension. Herbicide Guide for Iowa Com and Soybean 

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http://www.caes.uga.edu/commodities/fieldcrops/peanuts/2009peanutupdate/documents/Pe 

anut_ Weed. pdf 

U.S. EPA. 1985. Chemical fact sheet for bentazon and sodium bentazon. Fact sheet no. 64. 

Office of Pesticide Programs. Washington, DC. 

U.S. Environmental Protection Agency (EPA). 2009-2013. Proprietary Data. 

U.S. Environmental Protection Agency (EPA). 2015. BEAD Response to the Dow 

AgroSciences Comments on Rice Production Practices and Use of Cyhalofop-butyl for 

Weed Control in Rice Production. Office of Pesticide Programs, Biological and Economic 

Analysis Division 

Zollinger, R.K., Christoffers, M., Dalley, C., Endres, G., Gramig, G., Howatt, K., Jenks, B., 

Lym, R., Ostlie, M., Peters, T., Robinson, A., Thostenson, A., and Valenti, H. 2016. North 

Dakota Weed Control Guide. Fargo, ND, North Dakota State University Extension Service, 

Publication W-253. Available at: https://www.ag.ndsu.edu/weeds/weed-control-guides/ndweed-control-guide-1 

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APPENDIX I. Guidance for Pesticide Registrants on Pesticide Resistance Management 

Labeling 

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, for 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; 

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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)." 

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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 lethal 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.pdO. 

Indicators of likely 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 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: 

I. 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 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 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 identified 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 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 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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