UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON D

.C., 20460 

### AUG 

## 20

## 2014
OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION MEMORANDUM


### SUBJECT:

FROM:



### THRU:



### TO: Rice Production Practices in the United States and Use ofCyhalofop-butyl for Weed Control in Rice Production (DP # 420989) Sunil Ratnayake, PhD, Biologist Biological Analysis Branch Biological and Economic Analys· AmetJones, Chief 

# ,**~'-~ rV\l<?..J~**  Division (7503P) Biological Analysis Branch Biological and Economic Analysis Di Jolene Trujillo, Chemical Review Manager Pesticide Re-evaluation Division (7508P)


### PeerReview Panel date: July 2, 2014
SUMMARY Environmental Fate and Effects Division (EFED) is currently working on a registration review analysis for mitigating risks involved withthe use ofcyhalofop (cyhalofop-butyl) inrice production. To facilitate this process, BEAD is providing needed informationto EFED ondrill (dry) seeded and water (wet) seeded rice production, use ofcyhalofop for weed control inthese production systems, and duration ofholding water following the applications ofcyhalofop in these rice production systems. Cyhalofop is a post-emergence herbicide used for selective control ofgrass weeds inrice production. Under drill seeded conditions cyhalofop is applied as post-emergence pre-flood, post-emergence post-flood (post-flood early applications, post-flood late ormid-season) applications. Early post-flood applications ofcyhalofop are made 7 to 10 days after the establishment ofpermanent flood. Also, late post-flood treatments are made in the mid-season as Page 1a salvage treatmentto save rice crop from higher weed infestations. Sequential applications of cyhalofop are also recommended under heavy grass weed infestations. According to available usage information (2008 to 2012), among the cyhalofop application timings, the highest amount ofcyhalofop (83 

### %) is applied as post-flood applications. Duration ofwater holding following a cyhalofop application varies depending onthe timing of cyhalofop application, time needed for the maturity ofplanted rice variety, and draining time of water in the field before harvesting. A longer duration ofwater holding, following a cyhalofop application is observed with rice varieties which need a longer maturation time, late draining of water before harvest, and earlier applications ofcyhalofop in a growing season. In this analysis, the longest duration ofwater holding (95 days) is observed with postemergence pre-flood application ofcyhalofop on a 130 day rice variety which is drained 14 days before harvest. The shortest duration ofwater holding (43 days) is observed with post-flood late applications (midseason) ofcyhalofop on a 120 day variety which is drained 21 days before the harvest. Calculations made for these estimates are shown onthe pages starting from 8 to 14 ofthis document. Rice Production in the United States Rice is the staple food for more than halfofthe worldpopulation (USDA Economic Research Service, 2008). According to a 2013 NASS survey, Arkansas, California, Louisiana, Mississippi, Missouri, and Texas are major rice producing States inthe United States (Table 1). Arkansas has the highest acreage in rice production and Californiaproduces the highest yields in rice production inthe United States (Table 1 ). Also, usual planting and harvesting dates ofrice are shown in Table 2. Table 

### 1. Rice Production in the U.S. in 2013
Acres Harvested Total Production State (in 1000 acres) Yield/ Acre (lbs) (1000 cwt) Arkansas 1,070 7,560 80,888 California 561 8,480 47,574 Louisiana 413 7,300 30,135 Mississi.Qpi 124 7,400 9,176

Missouri 156 7,030 10,968

Texas 144 7,740 11,145 United States 2,468 7,694 189,886 Source: USDA, NASS, 2014.

Page 2

### Table 2. Typical Planting and Harvesting Dates ofRice in Different Rice Producing States 

### State Planting Harvesting Begin End Begin End Arkansas April6 June2 Aug. 29 Oct. 24 California April20 June 10 Sep. 5 Nov. 10 Louisiana March20 May 15 July 27 Sep.28 Mississippi April6 May24 Aug. 29 Oct. 20 Texas March 17 May 10 July 29 Sep.20 Source. USDA, NASS, 2010 

### Rice Production Systems in the United States Drill Seeding (Dry Seeding) Under drill seeding dry seeds are planted in well leveled fields in rows using mechanical planters. Pre-plant herbicides are applied inthe field before planting seeds. After planting, levies are built and fields are flushed (irrigating and draining ofexcess water inthe field) in orderto soak seeds to facilitate seed germination. Before the emergence ofseedlings, pre-emergence herbicides are applied. Depending on the soil temperature and soil moisture, it takes about 7 to 12 days for seedling emergence following flushing ofrice fields. After the emergence of seedlings, fields are maintained with a low level ofwater (shallow flooding). Three to four weeks after planting, the permanent flooding is established with 6-12 inches ofwater and postflood herbicide treatments are applied to control existing weeds. Permanent flood is maintained until 2 to 3 weeks before harvesting and then the flooded water is drained to dry the field and to facilitate harvesting. This also helps reducing the moisture level in maturing seeds. Water Seeding (Wet Seeding) Water seeding is a commonproductionmethod in southern Louisiana and areas in Texas and California (Arkansas Rice Production Handbook, Undated). Inthis production system, following the land preparation and pre-emergence treatments, fields are flooded before seeding and pregerminated or dry seeds are broadcasted over the flooded fields using an airplane. Most ofthe wet low lands can be used for this production system. The primary reasons for water-seeding are for red rice suppression, reduced labor and reduced inputs. Also, it is an alternative production system that can be used when heavy rainfall is interfering with drill seeding. Furthermore, use of this production system, allows rice farmers to raise crawfish inrice production fields (Louisiana Rice Production Handbook, 2009). In addition, water seeding is a production system that canbe used to control weeds effectively. Especially, broadleafand grass weeds, including red rice. The water seededproduction systemtends to favor sedges and other aquatic weeds. Hydrilla (Hydrilla verticillata) waterhyssop (Bacopa rotundifolia), duck salad (Heteranthera limosa), purple ammannia (Ammannia coccinea), goose weed (Spehenoclea zelanica), and arrowhead (Sagittaria montevidensis) are some ofthe aquatic weeds found inthe water seeded rice Page 3production. (University ofAR, Rice Production Handbook, Undated). On the basis ofwater management, water-seeded rice can be categorized as delayed flooding, pinpoint flooding, and continuous flooding (LouisianaR_.ice Production Handbook, 2014). DelayedFlooding Under the delayed flooding system, fields are flooded before water seeding. Just after seeding, fields are drained to a shallow level, which is maintained for 3 to 4weeks before the permanent flood is established. Delayed flooding is adopted in fields where red rice is not a serious problem (Louisiana Rice Production Handbook, 2014). Flooded water is drained 2 to 3 weeks before harvesting. PinpointFlooding Underpinpoint flooding, a thin layer ofwater is maintained inthe field before pre-germinated or dry seeds are broadcasted aerially overthe fields. The thin layer ofwater is maintained until the seedlings are well established (7 to 10 days). An advantage ofthis method is it enhances seed germination. Two to 3 weeks after seeding, the permanent flood (six to eight inches ofwater) is established and maintained until 2 to 3 weeks before harvesting. Finally the flooded water is drained to drythe fields. This practice facilitates the use ofmechanical harvesters and reduces seed moisture in maturing seeds. Continuous Flooding Under continuous flooding, once the fields are flooded before seeding, water is not drained for improving the seed germination. Water level is maintained at 6 to 12 inches inthe field continuously until 2 to 3 weeks before harvesting. Ofthese three water management systems, the continuous flooding system is the best water management system for red rice suppression. However, the proper seedling establishment is difficult under this method. Weed Control in Rice Production Compared to the other field crops, weed management in rice production is a significant challenge for rice farmers. Bothpre-emergent andpost-emergent herbicides are used to control weeds in rice production. Mostly, pre-emergence herbicides are applied inthe field before planting rice seeds. However, under certain situations they can be applied after the planting ofrice, but before the emergence ofweeds. Under drill seeded condition, before planting ofrice seeds, preemergent herbicides are applied to kill germinating weed seeds in the soil. Use ofa preemergence herbicide with residual activityprolongs the duration ofweed control after the crop establishment. Herbicides such as pendimethalin, molinate, thiobencarb, quinclorac are some of the pre-emergence herbicides used inrice production. Afterplanting ofrice, levies are built and fields are irrigated to facilitate a uniform germination ofrice seeds. Depending onthe moisture level in soil, rice fields may be irrigated several times before the establishment ofpermanent flood. Permanent flooding helps in controlling many grass and broadleafweeds. The drill seeded production system favors grass and broadleafweed species. Generally, barnyard grass (Echinochloa crus-galli), broadleafsignal grass (Brachiariaplatyphylla), crabgrass (Digitaria sanguinalis and Digitaria ischaemum), panicum (Panicum dichotomiflorum), and sprangletop Page4(Leptochloa spp.) are the troublesome grass weeds found inthe rice pr6duction. Carfentrazoneethyl, bentazon, acifluorfen, cyhalofop, propanil 

### +bensulfuron, quinclOnic, triclopyt, bensulfuron, dichloropropionanilide, and halosulfuron are some ofthe post-emergence herbicides used inthe rice production (Rice Production Guidelines, Texa.S Agric. Experiment Station, 2012). Usage ofCyhalofop in the United States Table 3. Average Usage ofCyhalofop inthe United States (2008 to 2012)

"tJ. ,_- 5-YearAverage "" State (Pounds ofActive 5-YearAverage .c

rr. Ingredient) Percent Crop Treated 

### (%) '· n Arkansas 32,912 5 California 23,804 10 Louisiana 7,916 5 Mississippi 9,950 11

Missouri 2,476 2

Texas 4,093 6 (Propnetary Data, 2008- 2012) The data in Table 3 shows the percentage ofcrop treated with cyhalofop in different states. On average, the states ofCalifornia and Mississippi indicate the most use with 10 and 11%, respectively. In the other states a lowpercentage ofrice crop was treated in with cyhalofop. Table 4. Average Usage and Percentage ofCyhalofopApplied at Different Application Timings Applic tion Timing Av. Usage (a.i.lbs) I Percentage 

### (%)



### ...**.** Pre-flood 13,155 17 Early post-flood 5,846 7 Late post-flood 60,272 76 (Propnetary Data, 2008- 2012). Based onthe proprietary data, total percentage ofcyhalofop applied before establishing the permanent flooding (pre-flood) is 17% (Table 4). Also, the percentage ofcyhalofop applied as early post-flood and late post-flood were 7% and 76%, respectively. The total% ofcyhalofop applied after the establishment ofpermanent flood (post-flood) was 83%. These herbicide applications are made in the field overthe crop and generally flooded water is drained two to three weeks before harvesting.
Page 5Application Methods and Weeds Controlled by Cyhalofop Cyhalofop is a selective post-emergence herbicide used for grass weed control inrice production. Itis a systemic herbicide absorbed by leaves and leafsheaths. This herbicide has no preemergent or soil residual activity. Cyhalofop canbe applied aerial or ground application methods. Major weeds controlled are; barnyardgrass (Echinochloa crus-galli), broadleaf signalgrass (Brachiariaplatyphylla), bearded sprangletop (Leptochloa fascicularis), early watergrass (Echinochloa oryzoides),junglerice (Echinochloa colona), large crabgrass (Digitaria sanguinalis), late watergrass (Echinochloaphyllopogon) and red sprangletop (Leptochloa filiformis) (Clincher® SF SpecimenLabel, 2009). Cyhalofop Application Rates. According to the cyhalofop specimen label (Clincher® SF. Specimen Label. 2009), more than 15 fluid ounces ofproduct (0.27lbs ofa.i. per acre) should notbe applied in a single application. Also, more than 25 fluid ounces ofproduct (0.46lbs a.i per acre) should not be applied during the growing season. Ifsequential applications are made they must be at least 1 0 days apart. Rain Fastness. According to (Clincher® SF. Specimen Label. 2009), cyhalofop is rain fast within 2 hours. Three hours after the herbicide application, field canbe re-flooded. Bestresults canbe achieved byflooding the field 24 to 48 hours after the herbicide application. Water Holding Period. There is no water holding period restriction following the application of this herbicide. Crop Rotation Interval The land should not be rotated to crops other than rice for 3 months following the cyhalofop application. Preharvest Interval. Cyhalofop should not be applied within 60 days ofrice harvest (both under drill and wet seeding systems).

Page 6Table 5. General Timeline for Rice Production in AR, LA, MS and TX1 CulturalPractice Duration Herbicide Treatment Landpreparation Early March to end ofMarch Pre-plant treatments Mid-Marchto Mid-April Planting (seeding) Firstweek ofApril Pre-emergence treatments After seeding_in April Flushing After seeding, fields are irrigatedto wetthe soil and then the water is drained to facilitate seed germination Seedling emergence Second week ofApril Pre

- permanent flood Mid to end ofApril Cyhalofop treatments Application Permanent flooding First week ofMay Post- permanent flood early Second week ofMay Cyhalofop treatments Application Post-permanent flood late Early to Mid-June Cyhalofop treatments (mid-season) Application Draining offlooded Water Second orThird week ofJuly Harvesting First week ofAugustto end of August
1Please note thatthis timeline for cultural practices mayvary depending onthe location, weather conditions (rainfall, air temperature) soil conditions (soil temperature, soil moisture) water management, and the rice variety used for planting. Timeline described is for a 120 day variety planted in first week ofApril. Cyhalofop Applications in Dry Seeded Rice Production Pre-permanent flood Application Application ofcyhalofop before establishingthe permanentflood. Flushingthe field may be needed to have a good soil moisture level priorto herbicide application
. Ifthe field is irrigated to enhance seed germination, watermustbe drained before the herbicide application and to expose weeds for a good herbicide coverage. Fields canbe re-flooded three hours after the herbicide application and best results canbe achieved by flooding fields 24 to 48 hours after the herbicide application. Post-permanent flood early Application. Application ofcyhalofop 7 to 10 days after the establishment ofpermanent flood. Field must be drained priorto herbicide applicationto expose the weeds (at least 70%) for a good herbicide coverage (Clincher® SF. SpecimenLabel. 2009). Permanent-flood (mid-season) Application. Application ofcyhalofop 6 to 8 weeks after planting to control existing grass weeds inthe field. This applicationis also considered as a salvage treatmentto minimize the yield reduction due to a higher weed infestation. Page 7

### Estimated duration ofwaterholdingfollowing herbicide applications in AR, LA, MS and TX (please note that estimated durations mayvary depending on theweather condition, duration ofthe rice variety, and location). Duration ofHoldingWaterin the Field underDrill Seeding (Dry 

### Seeding) 1. Duration ofholding water inthe field following the pre-flood applications Estimated upper range 120- 21

- 14 = 85 days (120 day variety. cyhalofop is applied 21 days after planting and before establishing the permanent flood. Field is drained 14 days before harvesting) Estimated lower range 120

- 21

- 21= 78 (cyhalofop is applied 21 days after planting and before the permanent flooding. Field is drained 21 days before harvesting) 2. Duration ofholding water after post-flood early applications Estimated upper range

120-31 -14 = 75 days (120 day variety, cyhalofop is applied 32 days after planting. Fieldis drained 14 days before harvesting). Estimated lower range 120-31- 21= 68 days (cyhalofop is applied 32 days after planting. Field is drained 21 days before harvesting). 3. Duration ofholding water after post-flood late (mid-season) applications Estimated Upper Range 120- 56- 14 =50 days (cyhalofop is applied 56 days after seeding and field is drained 14 days before harvesting). Estimated Lower Range 120- 56- 21 = 43 days (cyhalofop is applied 56 days after seeding and field is drained 21 days before harvesting).

Page 8Table 6. Timeline for Water (Wet) Seeding and Cyhalofop applications2 CulturalPractice Duration HerbicideApplication Land Preparation In March Flooding Early April before seeding Seeding (broadcasting of Early April after flooding germinated seeds or

### dry seeds overthe flooded fields) Pre-permanent flood In late April before establishing Application ofcyhalofop treatment the permanent flood Permanent flooding Early May Postpermanent flood early 7 to 1 0 days afterpermanent Cyhalofop Application treatments flooding Post-flood-late treatments 6 to 8 weeks after seeding Cyhalofop Application (mid-season applications) Draining offlooded Water Second or third week ofJuly Harvesting Beginningto end ofAugust 2Please note that this timeline for cultural practices may vary depending on location, weather conditions (rainfall, air temperature) soil conditions (soil temperature, soil moisture) water management, and the rice variety used for planting. Timeline described is for a 120 day variety planted in first week ofApril. Cyhalofop Applications in Water Seeded (Wet Seeded) Rice Production Pre-permanent flood application Application ofcyhalofop after flooding and before the establishment ofpermanent flood. Post permanent flood early application A single post flood application is recommended 7 to 10 days afterpermanent flooding. Field mustbe drained before the application to expose weeds for a better coverage Postpermanent flood late application Application ofcyhalofop 6 to 8 weeks afterplantingto control existing grass weeds inthe field. This application is also considered as a salvage treatmentto minimize the yield reduction due to a higher weed infestation.

Page 9

### Estimated duration ofwaterholding afterherbicide applications in AR, LA, MS and TX (please note that estimated durations mayvary depending on theweather conditions, duration ofthe rice variety used forplaning and location). 1. Duration ofholding water following the pre-permanent flood applications Estimated upperrange

120-21

- 14 = 85 days (120 day variety. Cyhalofop is applied 21 days after seeding and field is drained 14 days before harvesting). Estimated lower range 120-21- 21= 78 days (120 day variety. (Cyhalofop is applied 21 days after seeding and field is drained 21 days before harvesting). 2. Duration ofholding water after post- permanent flood early applications Estimated Upper Range 120-31- 14 = 75 days (120 day variety. Cyhalofop is applied 31 days after seeding and field is drained 14 days before harvesting). Estimated LowerRange 120

- 31

- 21= 68 days (120 day variety. Cyhalofop is applied 31 days after seeding and field is drained 21 days before harvesting). 2. Duration ofholding water after post-flood late (mid-season) applications Estimated Upper Range 120- 56- 14 =50 days (120 day variety. Cyhalofop is applied 56 days after seeding and field is drained 14 days before harvesting). Estimated LowerRange 120

- 56

- 21= 43 days (120 day variety. Cyhalofop is applied 56 days after seeding and field is drained 21 days before harvesting).

Page 10Figure 1. Growth Stages ofa Rice Variety Gown in California (Drill Seeded Variety)

L

...

r:st"Yt' 1 2 3 4**~** Days: Early variety 25 - 30 Days: LoloYef1e1Y 25 - 30

# I~ Pre-flood cyhalofop Applications Tiler l'1llallon
Post flood applications Mid Tllemg 55-60 65-75

Mid-season cyhalofop Applications Source: Crop Profile for rice in California. 1988
. 85-100 100-115 130 - 145 140-165 

### Hwvo«l

This figure shows different growth stages ofrice afterplanting and stages ofcyhalofop applications. The different timing may vary depending on the weather, location, and the rice variety used for planting.

Page 113 Table 7. General Timeline in CaliforniaRice Production Drill (dry) Seeding' CulturalPractice 

### Timin£ HerbicideApplication Land Preparation Early March Pre-planttreatments Mid-March to Mid-April Planting Third week ofApril Pre-emergence treatments Third week ofApril Flushing In the third week ofplanting, fields are irrigated to wetthe soil and drained to facilitate seed germination. Seedling Emergence Fourth week ofApril Post-emergence pre-flood First week ofMay Cyhalofop Application treatments Permanent flooding Second week ofMay Post-flood early treatments Fourth week ofMay Cyhalofop application Post-flood late applications Mid-June Cyhalofop application (mid-season) Draining offlooded water Mid to end ofJuly Harvesting Mid-Augustto Mid-September 3Please note that this timehne for cultural practices mayvary depending on location and weather conditions (rainfall, airtemperature) soil conditions (soil temperature, soil moisture) water management, andthe rice variety used for planting. Timeline described is for a 130 day variety planted inthird week ofApril. Duration ofHolding Water under Drill Seeding (Dry Seeding) 1

). Duration ofholding water inthe field following the pre-permanent flood application of cyhalofop. Estimated upperrange 130- 21

- 14 = 95 days (130 day variety. cyhalofop is applied 21 days after planting and field is drained 14 days before harvesting). Estimated lower range 130

- 21

- 21 = 88 days (130 day variety. cyhalofop is applied 21 days after planting and field is drained 21 days before harvesting). 2. Duration ofholding water following the post-flood early applications Estimated upper range

130

- 31 -14 = 85 days (130 day variety. Cyhalofop is applied 31 days after seeding and field is drained 14 days before harvesting).
Page 12Estimated lower range 130- 31

- 21= 78 days (130 day variety. Cyhalofop is applied 31 days after seeding and field is drained 21 days before harvesting). 3).Duration ofholding water following the post-flood late (mid-season) applications Estimated Upper Range 130- 56 -14 = 60 days (130 day variety). Cyhalofop is applied 56 days after seeding and field is drained 14 days before harvesting). Estimated Lower Range 130 -56

- 21= 53 days (130 day variety. Cyhalofop is applied 56 days after seeding and field is drained 21 days before harvesting). Table 8. General Timeline in California Rice Production Water (wet) Seeding 4 CultUral Practice Timing Herbicide Application



## ... Land Preparation Early March Pre-planttreatments Mid-Marchto Mid-April Flooding Third week ofApril Broadcasting ofgerminated Third week ofApril seeds or dry seeds (seeding) Pre-permanent flood Second week ofMay Cyhalofop application treatments Establishment ofpermanent Second week ofMay flood Post flood early treatments Third week ofMay Cyhalofop application Post-flood, late treatments Third week ofJune Cyhalofop application (mid- season) Draining ofwater Second or third week ofJuly Harvesting In September 4Please note thatthis timeline for cultural practices may vary depending on location and weather conditions (rainfall, soil moisture, soil temperature and the rice variety used for planting). Timeline described below is for a 130 day variety. 1). Duration ofholding water inthe field following the pre-permanent flood application of cyhalofop. Estimated upperrange 130- 21

- 14 = 95 days (130 day variety. cyhalofop is applied 21 days after planting and field is drained 14 days before harvesting). Estimated lower range 130- 21

- 21= 88 days (130 day variety. cyhalofop is applied 21 days after planting and field is Page 13drained 21 days before harvesting). 2. Duration ofholding water following the post-flood early applications Estimated upperrange

130

- 31 -14 = 85 days (130 day variety. Cyhalofop is applied 42 days after seeding and field is drained 14 days before harvesting). Estimated lower range 130

- 31- 21= 78 days (130 day variety. Cyhalofop is applied 42 days after seeding and field is drained 21 days before harvesting). 3).Duration ofholding waterfollowing the post-flood late (mid-season) applications Estimated Upper Range 130- 56 -14 = 60 days (130 day variety). Cyhalofop is applied 56 days after seeding and field is drained 14 days before harvesting). Estimated Lower Range 130 -56- 21=53 days (130 day variety. Cyhalofop is applied 56 days after seeding and field is drained 21 days before harvesting. As shown in above examples, duration ofwaterholding after applications ofdifferent herbicides canbe calculated for different rice varieties with known maturationtime, known herbicide application timings, and known draining timings ofwater before harvesting ofthe rice crop. REFERENCES: Arkansas Rice Production Handbook 192. Undated. Online Publication. Available at: http://www.arkansas-crops.com/wp-content/uploads/2014/02/MP192.pdf. Accessed onJune 6, 2014. Clincher® SF. Specimen Label. 2009. DowAgroSciences. Online publication Available at: http://www.cdms.net/LDat/ld5SF009.pdf. Accessed on June 5, 2014. Crop Profiles for rice in California. 1988. Online publication. Available at: http://www.ipmcenters
.org/cropprofiles/docs/carice.pdf
. Accessed on June 9, 2014. Louisiana Rice ProductionHandbook. 2014. Publication ofLouisianaAg Center. Available on line at: http://www.lsuagcenter.com/NR/rdonlyres/F7E930BF-346A-45DA-A989- 37FE3DOBOF11 I59612/pub2321RiceProdHdbkJune09
. pdf Accessed onJune 6. 2014. Page 14Proprietary Data, 2008- 2012. Rice Production Guidelines. 2005. Texas Agric. Experiment Station. USDA, ARS. http://beaumont.tamu.edu/eLibrary /Bulletins/2005 Rice Production Guidelines.pdf
. Accessed on June 5, 2014. Rice Background
. 2008. USDA Economic Research Service. http://www.ers.usda.gov/topics/crops/rice.aspx
. Accessed onJune 30
. 2014
. Shipp, M. Rice Crop Timeline for the Southern States ofArkansas, Louisiana, and Mississippi. Undated. Online Publication. Available at: http://www.cipm.info/croptimelines/pdf/Rice.pdf. Accessed on June 10, 2014.

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