I 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C .. 20460 

MAR 0 3 2015 

OFFICE OF 

PREVENTION, PESTICIDES AND 

TOXIC SUBSTANCES 

MEMORANDUM 

SUBJECT: 

FROM: 

THRU: 

TO: 

Benefit Assessment on the Use of Quinclorac in Rice Production (PC 

128974) 

Sunil Ratnayake, Biologist 

Biological Analysis Branch ~ V\1~ 

Jihad 

Science 

Alsadek, 

Information 

Economist 

and Analysis 

J"V~ Branch .pi-~ 

T J Wyatt, Economist -.A. '-1:! ( .... 

Economic Analysis Branch _ 1 ~ fi\J Zo f, ...lDtS' 

Biological and Economic Analysis Divi on (7503C) ~ 

Arnet Jones, Chief 

Biological Analysis Br 

Diann Sims, Chief~ Science Information and Analysis Branch 

Timothy Kiely, Chief (7\.-· J\A.. \.~ Economic Analysis Branch ~ j . C 

Biological and Economic Analysis Division (750 

Margaret Hathaway, Chemical Review Manager 

Risk Management and Implementation Branch RMB II 

Pesticide Re-evaluation Division (7503 P) 

PEER REVIEW PANEL: February 11, 2015 

SUMMARY 

As part of the re-evaluation process of registration of quinclorac, this document contains 

an assessment of benefits of the use of quinclorac in rice production. Quinclorac is a 

selective and systemic herbicide applied for the control of grasses and certain broadleaf 

weeds in rice production.Jt is widely used for the control ofpropanil resistant 

barnyardgrass biotypes. Qpinclorac can be applied either pre-emergence, postPage 1 
emergence, or as a late-season salvage treatment to control grasses and some broadleaf 

weeds found in the rice production. Clomazone, pendimethalin, and thiobencarb are 

available alternative pre-emergence treatments for control ofbamyardgrass. Similar to 

quinclorac, these herbicides provide residual activity. Bispyribac-sodium, cyhalofopbutyl, fenoxaprop, propanil, pendimethalin, penoxsulam, clomazone, and thiobencarb are 

herbicides that can be used as post-emergence treatments. 

Quinclorac provides a wide application window and can be applied as pre-emergence, 

early post-emergence or late-season salvage treatment in drill seeded rice_ and as an early 

post-emergence foliar treatment or late-season salvage treatment in water seeded rice. 

Despite the activity against grassy weed species, quinclorac will generally not cause 

herbicide injury to the rice crop. Furthermore, according to the classification of 

mechanism of action of herbicides, quinclorac belongs to the mechanism of action Group 

4 (WSSA, Undated 2). It is often tank-mixed with other herbicides such as clomazone 

(Group 13), pendimethalin (Group 3) propanil (Group 7), and thiobencarb (Group 8) to 

minimize the development of herbicide resistance in weed species found in rice 

production. In addition, the weed spectrum controlled by the individual herbicide varies 

considerably and by tank-mixing of these herbicides, compatible herbicides can be 

applied in a single application to minimize the cost of herbicide application and achieve a 

broader spectrum of weed control. 

Usage Information on Quinclorac 

On the basis of available proprietary data, the highest agricultural usage of quinclorac is 

for weed control in rice production. Nationally, about 300 thousand pounds active 

ingredient (lbs. a.i.) of quinclorac is applied annually on rice with an average of 30 

percent crop treated (BEAD, 2012). This usage on rice was mainly in Arkansas, 

Louisiana, Mississippi, Missouri, and Texas. The p.igh proportion of rice treated with 

quinclorac suggests that it provides benefits to rice growers. Quinclorac can be applied 

either pre-emergence, post-emergence, or as a late-season salvage treatment to control 

grasses and some broadleaf weeds that escape previous applications or emerge later in the 

season. Also, quinclorac is widely used for the control of propanil resistant 

bamyardgrass biotypes found in the rice production (WSSA, Undated) 

In the United States, rice is grown in Arkansas, California, Louisiana, Mississippi, 

Missouri, and Texas (USDA ERS, 2013). Arkansas, with over 42% ofthe nation's total 

rice production, produces more rice than any other state. In 2013, about 1.1 million acres 

of rice were harvested in Arkansas, with total production of 81 million cwt (USDA ERS, 

2014). Between 2008 and 2012, about 45 percent of the rice acreage in Arkansas was 

treated with quinclorac (Proprietary data, 2009-2013). About 60 percent of the acreage is 

treated by air even though aerial applications are proscribed in some areas around 

Crowley's Ridge in Poinsett and Craighead Counties to prevent damage to other crops 

from potential spray drift. 

Usage of quinclorac in California is limited and according to proprietary data (2009-

2013), less than ten percent of the rice area was treated for bamyardgrass control. 

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Given the importance of rice production and the extent of usage of quinclorac in the state, 

Arkansas is the primary focus of this document, but the results are indicative of the role 

quinclorac plays throughout rice production in the region. 

Use of Quinclorac in Rice Production 

Quinclorac is a selective and systemic herbicide applied for the control of grasses and 

certain broadleaf weeds in rice production. Quinclorac can be applied as a preemergence, or early post emergence treatment in drill seeded rice and post-emergence 

foliar treatment on water seeded rice. Also, quinclorac can be applied as a late-season 

salvage treatment in rice production systems (Bennett, 2003). In Arkansas, most of 

quinclorac usage is as post-emergence treatments (proprietary data, 2009-2013). 

According to proprietary survey data, rice growers primarily target barnyardgrass with 

the use of quinclorac. Weed control experts in Arkansas estimate 70% yield reduction of 

rice can occur due to the heavy, season long weed interference ofbarnyardgrass (Univ. of 

Arkansas, 2013). The problem is exacerbated because biotypes of weeds with resistance 

to several herbicides, including clomazone, propanil, and quinclorac, have been found in 

Arkansas (WSSA, Undated). Currently, !hese three herbicides are the most widely used 

herbicides, in terms of area treated, for the control of barnyard grass in the rice 

production as shown in Table 1 (Proprietary Data, 2009-2013 ). 

T a e bl 1 H er b" ICI "d e use fi or b d arnyar Lgrass con tr o l . th IJl e nee pro d uc f wn . 

Average area treated for Average cost per acre 2 

Chemical barnyardgrass (2009-20 13) ($) 

Quinclorac 749,000 18.10 

Bispyribac-sodium 68,000 27.40 

Clomazone 1,197,000 11.30 

Cyhalofop-butyl 144,000 29.50 

Fenoxaprop 92,000 24.70 

Pendimethalin 89,000 6.60 

Penoxsulam 39,000 19.40 

Propanil 608,000 16.30 

Thiobencarb 92,000 13.40 

Source: Proprietary data, 2009-2013. 

1 Alabama, Arkansas, Louisiana, Mississippi, and Missouri. 

2 Average chemical cost per acre for a treatment targeting barnyard grass across acres 

treated with varying application rates. 

Available Alternatives 

Weed management decisions in rice are made based on the situations in individual fields. 

It requires a good knowledge ofthe types of weeds in the field, efficacy ofherbicides on 

different weeds, herbicide application timing, application rates, and residual effects. 

Moreover, herbicide selection must consider potential injury to the rice, especially 

herbicides for control of grass weed species. Resistance management practices, such as 

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tilling, crop rotation, and the use of herbicides with different modes of action are 

important to minimize the development of weed re.sistance in rice production. Many 

registered herbicides are available as alternatives for the weed control in rice production. 

A list of these herbicides that can be used at different application timings in rice 

production is given in Table 2. In addition to controlling grass weed species, including 

barnyard grass, these herbicides controls certain broad leaf weed species found in the rice 

production. As shown in Table 2, spectrum of weeds controlled by the individual 

herbicide varies and depending on the weed spectrum found in the field, effective 

herbicides on different weeds can be tank-mixed and applied in a single application to 

minimize the development of weed resistance, cost of herbicide application, and to 

achieve a broader spectrum of weed control. 

Clomazone is the most commonly applied pre-emergence treatment and it is relatively 

inexpensive than other herbicides (Table 1). Clomazone provides residual activity and it 

can also be applied as pre and post-emergence treatments. However, it is rarely applied as 

post-emergence treatment for weed control in rice production. Only one application of 

clomazone per year is allowed under the label. According to proprietary data, rice 

growers rarely use pendimethalin and thiobencarb for the grass weed control including, 

barnyard grass despite the fact that they are relatively inexpensive (Table 1 ). Also, both of 

these herbicides have relatively narrow windows for pre-emergence applications to avoid 

injury to the rice. Early post-emergence applications of these chemicals are often tankmixed with other compatible herbicides, including quinclorac, to provide broader 

spectrum of weed control including broadleafweeds (Univ. of Arkansas, 2013). 

Quinclorac is commonly applied as post-emergence treatments for weed control in rice 

production. Cyhalofop-butyl, fenoxaprop, bispyribac-sodium, propanil, pendimethalin, 

penoxsulam, clomazone, and thiobencarb also can be used as post-emergence treatments 

for weed control in rice production. Propanil and quinclorac are extensively used for 

weed control in rice production (Table 1). Due to the extensive use of these herbicides, 

certain biotypes of barnyardgrass have developed resistance to both of these herbicides 

(Univ. of Arkansas, 2013). Bispyribac-sodium and cyhalofop-butyl can also be used as 

late-season salvage treatments. However, proprietary data indicate that growers rarely use 

these herbicides and they are more expensive than the quinclorac (Table 1 ). Bispyribacsodium does not provide residual weed control. However, bispyribac-sodium and 

penoxsulam more commonly used for broadleaf weed control and they are effective on 

controlling bamyardgrass found in the rice production. In addition, cyhalofop-butyl and 

fenoxaprop are effective for bamyardgrass control, including biotypes resistant to 

propanil and quinclorac. However, they cannot be mixed with some common herbicides 

used for broadleaf weed control (Univ. of Arkansas, 2013). 

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Table 2. H~rbicides Used as Alternatives to Quinclorac for Weed Control in Rice 

Production1

• 

Stage of Remarks Application Herbicide 

Clomazone is a pre-emergence herbicide with residual activity. It is applied for weed 

control in dry seeded rice, 14 days before or 7 days after the drill seeding of rice activity. 

Clomazone Clomazone controls annual grasses and some broadleafweeds. Major grassy weeds 

controlled are bamyardgrass, braadleaf signalgrass, crabgrass, panicum species, and 

sprangletop. Majorbroadleafweeds controlled are spurred anoda, velvetleaf, ragweed, 

lambs quarter. Clomazone does not have a late post-emergence activity and it can be 

applied only once per season. 

Pre-emergence 

Pendimethalin can be applied as pre-emergence or early post-emergence treatments. It has 

Pendimethalin a long residual activity. In addition to bamyardgrass, it is effective on sandbur, goosegrass, 

Post-emergence witchgrass, crabgrass, junglerice, seedling johnsongrass, crowfootgrass, sprangletop, 

broadleaf signal grass, and panicl!ffi species. Pendimethalin is applied only after rainfall or 

shallow irrigation for the germination of rice seeds. 

Thiobencarb Thiobencarb is applied as a delayed pre emergence treatment. It provides "excellent 

control of sprangletop, bamyardgrass and several aquatic weeds. Thiobencarb provides 

residual activity. Applications of this herbicide are made I to 5 days before rice 

emergence or about 5 to 9 days after planting, 

Clomazone can be applied as an early post-emergence treatment at I to 2 leaf stage of rice. 

Clomazone It controls annual grasses and some broadleafweeds. Major grassy weeds controlled are 

bamyardgrass, broadleaf signalgrass, crabgrass, panicum species, and sprangletop. Major 

broadleafweeds controlled are spurred anoda, velvetleaf, ragweed, lambs quarter. It can 

be tank mixed with quinclorac. Clomazone does not have a late post-emergence activity 

Fenoxaprop can be applied as a post-emergence treatment to control annual grasses in rice 

Fenoxaprop production. Foliar coverage of emerged grasses is important. Controls bamyardgrass, 

broadleaf signalgrass, fall panicum, seedlingjohnsongrass, and sprangletop. Irrigated 

water must be drained from the field prior to fenoxaprop application to expose the weeds. 

Fenoxaprop is not as effective as other chemicals on broadleaf species. 

Propanil is applied as a post-emergence herbicide to control grassy weeds and some 

Post-emergence broadleafweeds in rice production. Propanil is effective in controlling barnyard grass. Due 

Prop ani! to the extensive use, biotypes ofbamyardgrass have develop resistance to this herbicide. In 

addition to bamyardgrass propanil controls crabgrass, broadleaf signalgrass, goosegrass, 

panicum species, foxtail species, and broadleafweed species such as woolly croton, curly 

dock, hemp sesbania, and redroot pigweeds. Propanil does not have residual activity and to 

broaden the weed control spectrum and efficacy, propanil can be tank mixed with 

quinclorac, pendimethalin, clomazone and thiobencarb. 

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Stage of Remarks Application Herbicide 

Pendimethalin can be applied as an early post-emergence treatment. It has a long residual 

activity. Pendimethalin can be tank mixed with herbicides such as propanil, quinclorac, 

Pendimethalin 

thiobencarb and clomazone to brpaden the spectrum of weed control. In addition to 

bamyardgrass, it provides a good control of grass weeds such as field sandbur, goosegrass, 

witchgrass, crabgrass, junglerice, seedling johnsongrass, crowfootgrass, sprangletop, 

broadleaf signalgrass, and panicum species. To have a better weed control application s of 

this herbicide should be made at 1-3 leaf stage of the bamyardgrass. 

Thiobencarb can be applied as a post-emergence treatment to control grassy and some Thiobencarb broadleafweeds. The post-flood applications ofthiobencarb control weed species such as 

bamyardgrass, junglerice, spamgletop, duck salad, and redstem. If needed, thiobencarb 

can be tank mixed with other herbicides such as clomawne, pendimethalin, propanil, and 

quinclorac to increase the efficaoy and range of weed control. 

Cyhalofop-butyl Cyhalofop-butyl is a broad spectrum grass herbicide which controls tough grasses such as 

prop ani! and quinclorac resistance bamyardgrass, sprangletop, broadleaf signal grass, fall 

panicurn, knot grass, and jungle rice. It offers a broad application window and can be 

applied from 1-2 leaf stage to 60 days before harvest. 

Bispyribac-sodium has a broad application window and can be applied as pre-flood, postBispyribac-sodium flood, or late post-treatments. It provides a good control ofbamyardgrass and rice 

flatsedge. In addition, this herbicide controls johnsongrass, duck salad, dayflower, Indian 

joint vetch, Pennsylvania smartweed, and northern joint vetch. This herbicide does not 

have residual activity. To increase the spectrum of weed control, bispyribac-sodium can be 

tank mixed with thiobencarb, 2, 4 -D, clomawne, and pendimethalin. 

Penoxsulam is applied as a post-emergence treatment on rice from seedling emergence 

(drill seeded rice) to 60 days before harvest. Penoxsulam controls broadleaf and certain 

Post-emergence grass weeds in rice production, including barnyard grass, junglerice. Eclipta, hemp Penoxsulam sesbania, rice flatsedge, cocklebur, duck salad, pigweed, and smartweed are the other weed 

species controlled by penoxsulam. To increase the weed control spectrum this herbicide 

can be tank mixed with propanil, quinclorac, pendimethalin and other compatible 

herbicides. 

Bispyribac-sodium 

Bispyribac-sodium can be applied as a mid-season salvage treatment. It is effective in 

controlling propanil resistant bamyardgrass. In addition, it controls rice flatsedge. 

Later season Johnsongrass, duck salad, dayflower, Indian joint vetch, Pennsylvania smartweed, and 

northern joint vetch. To increase the weed control spectrum bispyribac-sodium can be tank 

(mid-season) mixed with herbicides such as thiobencarb, 2, 4-D, clomawne, and pendimethalin salvage 

treatment 

Cyhalofop-butyl Cyhalofop-butyl offers a broad application window and it can be applied from 1-2 leaf 

stage of rice to 60 days before harvest. It is a broad spectrum grass herbicide and effective 

against propanil and quinclorac resistant bamyardgrass biotypes. Cyhalofop-butyl does not 

have a residual activity. 

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Stage of Remarks Application Herbicide 

Quinclorac is applied for the control of grassy weeds, and certain broadleafweeds .. Rice 

Pre-emergence, 

crop has an excellent tolerance to quinclorac and does not typically damage the rice crop. 

Quinclorac provides a long term residual activity and it is applied as pre emergence, post 

Post emergence, or as a mid-season salvage treatment. It can be tank mixed with pendimethalin, 

emergence, and Quinclorac propanil, clomazone or thiobencarb. It is effective in controlling grassy weeds such as Mid-season broad leaf signal grass, crabgrass and bamyardgrass, including some propanil resistance 

salvage bamyardgrass biotypes susceptible to quinclorac. Also, quinclorac controls some broadleaf 

weeds such as hempsesbania,jointvetch, eclipta, and momingglory. In addition, it 

provides late post emergence activity. Quinclorachas a wider application window, broad 

spectrum of weed control, and it is effective on grassy weeds including propanil-resistant 

bamyardgrass biotypes which has not developed resistance to quinclorac. 

Source: (CDMS, Undated); Umv. of Arkansas, 2013. 1

For more information on herbicide application timing, rice production systems, and comparison of efficacy of the listed herbicides, 

please refer to Univ. of Arkansas Rice Production Handbook, 2013. Available at: 

: /www.uaex.edu/ ubhcations/ d£ m I m I 2. df 

Benefits of Quinclorac 

Quinclorac provipes excellent control of barnyard grass, although some biotypes have 

developed resistance. It also provides control of st?veral other important weed species, 

including broadleaf signalgrass, crabgrass, morningglory, and hemp sesbania (Univ. of 

Arkansas, 2013). Rice has an excellent herbicide tolerance for quinclorac (quinclorac 

does not cause herbicide injuries on rice crop). Also, quinclorac has a broad application 

window and it can be applied as a pre or post-emergence treatment in drill seeded rice 

and post emergence treatment on water seeded rice. Furthermore, depending on the weed 

situation, quinclorac can be applied as a mid-season salvage treatment to control grassy 

weeds which escaped early season herbicide treatments. In addition to grass weeds, 

quinclorac controls certain broadleaf weed such as· eclipta, Northern jointvetch, pitted 

morningglory, and palmleafmorningglory (Univ. of Arkansas, 2013). Quinclorac belongs 

to HRAC mechanism of action Group 4 and it is often tank-mixed or rotated with other 

herbicides such as clomazone (Group 13), pendimethalin (Group 3) propanil (Group 7), 

and thiobencarb (Group 8) to broaden the spectrum of weed control and minimize the 

development of herbicide resistance in weeds found in rice production. 

REFERENCES: 

BEAD (Biological and Economic Analysis Division). 2012. Screening Level Estimates of 

Agricultural Uses ofQuinclorac. 

Bennett, D. 2003. Facet plays big role in Arkansas rice. 

http://deltafarmpress.com/mag/farming facet plays big/. Accessed on Jan. 30, 

2015. 

Crop Data Management Systems, Inc. (CDMS). Undated. 

http:/ www.cdms.net/l~belsmsds lmdefault.aspx. Accessed on Feb, 2, 2015. 

Proprietary Data, EPA. 2009 to 2013. 

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

Arkansas Division of Agriculture, Cooperative Extension. Publication No. MP 

192. Online Publication. Available at: 

http://www.uaex.edu/publications/pdf!MP192/MP192.pdf. Accessed on Jan. 15, 

2015. 

USDA ERS. 2014. Rice Year Book. Economic Research Service, U.S. Department of 

Agriculture. Available at http://www.ers.usda.gov/data-products/rice-vearbook2014.aspx. Accessed on Jan. 29, 2015. 

Weed Science Society of America (WSSA). (Undated). Multiple resistant barnyardgrass 

(Echinochloa crus-galli) resistance to herbicide groups C2/7, and 0/4 USA: 

Arkansas. http://www. weedscience.org/Case/Case.asp?resultsiD= 1188. Accessed 

on January 30, 2015. 

Weed Science Society of America (WSSA) (Undated). Summary of Herbicide 

Mechanism of Action According to the Weed Science Society of America. 

Available at: http:/ /wssa.net/wp-content/uploads/WSSA -Mechanism-ofAction. pdf. Accessed on February 23, 2015. 

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