UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON D
.C. , 20460 

## MAY 2 82015

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION MEMORANDUM
SUBJECT:
FROM:

THRU:

TO: Rice Production Practices inthe United States and Use ofCyhalofop-butyl for Weed Control in Rice Production, Revised (DP#420989) Sunil Ratnayake, PhD, Biologist

# ~**Ak-VVV\~** Biological Analysis Branch

## ~ '"'" '

## ~__ 

## l Biological and Economic Analysis Division (7503P) Arnet Jones, Chief

# ~ Biological Analysis Branch Biological and Economic Analysis Divisi Jolene Trujillo, Chemical Review Manager Pesticide Re-evaluation Division (7508P) (7503P)

Peer Review Panel date: March 3, 2015
SUMMARY This document revises and replaces a previous version from July, 2014. Environmental Fate and Effects Division (EFED) is currently working on a risk assessment for mitigate risks involved withthe use ofcyhalofop (cyhalofop-butyl) inrice production. To facilitate thisprocess, BEAD is providing information ondrill (dry) seeded and water (wet) seeded rice production, use ofcyhalofop for weed control, and duration ofholding water following the applications ofcyhalofop inthese rice production systems. Cyhalofop is a post-emergence herbicide used for selective control ofgrass weeds inrice production. Underdrill seeded conditions cyhalofop is applied as post-emergence pre-flood and post-emergence post-flood (post-flood early andpost-flood late) treatments. Early post-flood applications ofcyhalofop are made 7 to 10 days afterthe establishment ofpermanent flood and Page 1this timing may vary by several days depending onthe weather conditions and level ofweed infestation inthe field. Also, late post-floodtreatments may be made inthe mid-season to save the rice crop from higher weed infestations (salvage treatments). Sequential applications of cyhalofop are also made under heavy grass weed infestations (Clincher® SF Specimen Label, 2009). Sequential application can be made at 15 fl ozper acre 7 to10 days after the permanent flood followed by second application at the rate of 10 fl oz per acre 10 to 15 days later. According to available usage information (2008 to 2012), most cyhalofop (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 inthe field before harvesting. A longer duration ofwater holding following a cyhalofop application is needed withrice varieties with longer maturation time, late draining ofwater before harvest, and earlier applications ofcyhalofop inthe growing season. Inthis analysis, the longest duration ofwater holding (95 days) is estimated withpostemergence 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 estimated withpost-flood late applications (midseason) ofcyhalofop on a 120 day variety which is drained 21 days before the harvest. Calculations for these estimates are shown onpages 7 to 13. Rice Production in the United States According to USDANASS, Arkansas, California, Louisiana, Mississippi, Missouri, and Texas are major rice producing states, (Table 1 ). Arkansas has the highest acreage inrice production and Californiaproduces the highest yields inrice production inthe United States (Table 1). Also, usual planting and harvesting dates ofrice are shown in Table 2. Table 1. Rice Production inthe U.S. in 2013 Total Acres Harvested 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 Mississippi 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.
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### Table2. Typical Planting and Harvesting Dates ofRice in Different
.Rice Producing States 

### State r· 

### Plantin2 

### Harvestin2 Begin End Begin End Arkansas April6 June 2 Aug. 29 Oct. 24 California April 20 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 inwell leveled fields inrows using mechanical planters. Pre-plantherbicides are applied in the field before planting
.seeds. Afterplanting, levies are built and fields are flushed (irrigating and draining ofexcess water in the field) in orderto soak seeds to facilitate seed germination. Before the emergence ofseedlings, pre-emergence herbicides are applied. Depending onthe soil temperature and soil moisture, ittakes about 7 to 12 days for seedling emergence following flushing ofrice fields. Afterthe emergence ofrice seedlings, fields are maintained under a wet condition using rain water or by quick irrigation (flushing). Thepermanent flood will be established whenthe seedlings are with 4 to 5 leaves or atthe development of2nd tiller. Mostrice varieties achieve this stage within 4 to 6 weeks after planting. This timing may vary depending onthe location, type ofthe planted rice variety, (late orearly), soil moisture, soil fertility, and weather conditions. Atthe establishment ofpermanent flood, rice fields are flooded to a depth of4 to 10 inches ofwater. Maintaining a water level about 113 to 112 ofseedling height is important and seedlings should not be submerged. Following the establishment ofpermanent flood, post-flood herbicide treatments maybe applied to control the existing weeds in the field. Generally, permanentflood is maintained until 2 to 3 weeks before harvesting andthen drained. This also helps reduce the moisture level in maturing seeds. Water Seeding (Wet Seeding) Water seeding is a commonproduction method in southern Louisiana and areas in Texas and California (LouisianaRice Production Handbook, 2014; Texas Rice Production Guidelines, 2012; Crop Profiles for Rice in California, 1998). Inthis production system, following the land preparation andpre-emergence treatments, fields are flooded before seeding andpre-germinated ordry seeds are broadcasted overthe flooded fields using an airplane. Fields with emerged seedlings are maintained with a lowlevel ofwater (shallow flood) until the permanent flood is Page 3established. The primary reasons for water-seeding are suppression ofred rice and otherweeds, reduced labor and reduced inputs. Also, it canbe used when heavy rainfall interferes with drill seeding. In addition, water seeding can be used to control weeds, especially, broadleafand grass weeds, including red rice. However, water seeded production systemtends to favor sedges and other aquatic weeds such as hydrilla (Hydri/la verticillata) waterhyssop (Bacopa rotundifolia), duck salad (Heteranthera limosa), purple ammannia (Ammannia coccinea), goose weed (Spehenoclea zelanica), and arrowhead. (Sagittaria montevidensis) (University ofAR, Rice Production Handbook, Undated). Onthe basis ofwatermanagement, water-seeded rice can be categorized as delayed flooding, pinpoint flooding, and continuous flooding (Louisiana Rice Production Handbook, 2014). DelayedFlooding Underthe delayed flooding system, fields are flooded before seeding and after seeding, fields are drained and maintained to a shallow level (usually 3 to 4 weeks) until the permanent flood is established. Delayed flooding is adopted in fields where red rice is not a serious problem (Louisiana Rice Production Handbook, 2014). Finally, 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). Thenthe permanent flood is established and maintained until seeds reach the maturity. Finally the flooded water is drained to dry the fields. Draining offlooded water facilitates the use ofmechanical harvesters and reduces seed moisture in maturing seeds before harvesting
. Continuous Flooding Under continuous flooding, fields are flooded before seeding and continuously maintaineduntil 2 to 3 weeks before harvesting. The continuous flooding system is the best water management system for red rice suppression. However, proper seedling establishment is difficultunder this method. Weed Control in Rice Production Weed management in rice production is a significant challenge for rice farmers because water can carry pesticides, and it is difficult to use ground application equipment. Bothpre-emergent and post-emergent herbicides are usedto control weeds in rice production. Mostly, preemergence herbicides are applied inthe field before planting rice**se~ds** to kill the germinating weed seeds in soil. However, under certain situations they canbe applied after the planting of rice. Use ofa pre-emergence herbicide with residual activityprolongs the duration ofweed control after the crop establishment. Herbicides such as pendimethalin, clomazone, thiobencarb, and quinclorac are some ofthe pre-emergence herbicides used inrice production. Page4Afterplanting ofrice, levies are built and fields are irrigated and drained 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), broadleaf signal grass (BrachiariaplatyphyUa), crabgrass (Digitaria sanguinalis and Digitaria ischaemum), panicum (Panicum dichotomiflorum), and sprangletop (Leptochloa spp.) are the troublesome grass weeds found inthe rice production. Carfentrazone-ethyl, bentazon, acifluorfen, cyhalofop, propanil 

### + bensulfuron, quinclorac, triclopyr, bensulfuron, dichloropropionanilide, andhalosulfuron are some ofthe post-emergence herbicides used inrice production (Rice Production Guidelines, Texas Agric. Experiment Station, 2012). 

### Usage ofCyhalofop in the United States Table 3. Average Usage ofCyhalofop inthe United States (2008 to 2012)**~** -**~ ~-** **~** I 

### 5-YearAverage -**~~** 

### State i 

### (Pounds ofActive 1 : 

### 5-Y earAverage ' I 

### lngtedient) 

### II Percent Crop Treated (%)

- 

### -**~** -·- --· Arkansas 32,910 5 California 23,800 10 Louisiana 7,920 5 Mississippi 9,950 11

Missouri 2,480 2

Texas 4,090 6 (Proprietary Data, 2008- 2012) Table 3 shows the percentage ofcrop treated with cyhalofop in different states. On average, California and Mississippi have the mostuse with 10 and 11% ofthe crop treated, respectively. 

### Table 4. Average Usage and Percentage ofCyhalofop Applied at Different Application Timings



### Application Timing' 

## - Av. Usage (a.L**lb~)** - 

### Percentage (%} Pre-flood 13,150 17 Early post-flood 5,850 7 Late post-flood 60,270 76 (Proprietary Data, 2008

- 2012). Based on the proprietary data, about 1 7% oftotal pounds ofcyhalofop is applied before establishingthe permanent flood 17% (Table 4). The total% ofcyhalofop applied after the establishment ofpermanent flood (post-flood) was 83%. These herbicide applications are made Page 5inthe field over the crop and generally flooded water is drained two to three weeks before harvesting. Table 5. General Timeline for Rice Production in AR, LA, MS and TX1 Cultural Practice Duration Herbicide Treatment andpreparation Early March to end ofMarch Pre-planttreatments Mid-Marchto Mid-April Planting (seeding) First week 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 Midto end ofApril Cyhalofop treatments Application Permanent flooding First week ofMay Post- permanent flood early Secondweek ofMay Cyhalofop treatments Application Post-permanent flood late Earlyto Mid-June Cyhalofop treatments (mid-season)2 Application Draining offlooded Water Second orThird week ofJuly Harvesting First week ofAugust to end of August

1Please note thatthis timeline for cultural practices may vary depending on the 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.
2Pre-harvest interval for this application is 60 days. Cyhalofop Applications in Dry Seeded Rice Production Pre-permanent Flood Application Application ofcyhalofop is made before establishing the permanent flood. Flushing the field may be needed to have a good soil moisture level priorto herbicide application. Ifthe field is irrigated to enhance seed germination, water must be drained before the herbicide application and to expose weeds for goodherbicide coverage. Fields canbe re-flooded three hours after the herbicide application and best results can be achievedby flooding fields 24 to 48 hours afterthe herbicide application. Post-permanent Flood EarlyApplication. Application ofcyhalofop is made 7 to 10 days afterthe establishment ofpermanent flood. This timing may vary few days depending onthe field situation. Page 6Field must be drained priorto herbicide application to expose the weeds (at least 70%) for a good herbicide coverage (Clincher® SF. Specimen Label. 2009). Permanent-Flood (mid-season) Application. Application ofcyhalofop is made 6 to 8 weeks after planting to control existing grass weeds inthe field. This application is also considered as a salvage treatmentto minimize the yieldreduction due to a higher weed infestation. The preharvest interval for this application is 60 days. 

### Estimated duration ofwater holding in drill seeded rice following the herbicide applications in AR, 

### LA, MS and TX (please notethat estimated durations mayvary depending on the weather condition, duration ofthe ricevariety, and location). Duration ofHoldingWater in the Field under Drill Seeding (Dry 

### Seeding) 1. Duration ofholding water inthe field following the pre-flood applications Estimatedupper 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 (120 day variety. cyhalofop is applied 21 days after planting and before the permanent flooding. Field is drained 21 days before harvesting) 2. Duration ofholding water afterpost-flood early applications Estimatedupper range

120

- 32 -14 = 74 days (120 day variety, cyhalofop is applied 32 days after planting. Field is drained 14 days before harvesting). Estimated lower range 120

- 32

- 21= 67 days (120 day variety, 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 EstimatedUpper 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 Lower Range 120

- 56

- 21 = 43 days (120 day variety, cyhalofop is applied 56 days after seeding and field is drained 21 days before harvesting). Page 7Table 6. Timeline for Water (Wet) Seeding and Cyhalofop Applications 1 CulturalPractice Duration



### - HerbicideApplication Land Preparation In March Flooding Early April before seeding Seeding (broadcasting of Early April after flooding germinated seeds ordry 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 10 days after establishment of Cyhalofop Application treatments permanent flood. This timing may vary depending onthe level of weed infestation. Post-flood-late treatments 6 to 8 weeks after seeding. Cyhalofop Application (mid-season applications) 2 Draining offlooded Water Second or third week ofJuly Harvesting Beginning to end ofAugust 'Please note that in waterseededrice, only liquid formulation ofcyhalofop is applied. 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.
2Preharvest interval for this application is 60 days. Cyhalofop Applications in Water Seeded Rice Production Pre-permanent flood application Application ofcyhalofop is made after flooding and before the establishnient ofpermanent flood. Post permanent flood early application A single post flood application is recommended 7 to 10 days after permanent flooding. This timing may vary depending onthe level ofweed infestation. The field mustbe drained before the application to expose weeds for a bettercoverage Postpermarient flood late application Application ofcyhalofop is made 6 to 8 weeks afterplanting to control existing grass weeds in the field. This application is also considered as a salvagetreatmentto minimize the yield reduction due to a higher weed infestation.

Page 8

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

120

- 21

- 14 = 85 days (120 day variety. Cyhalofop is applied 21 days after seeding and field is drained 14 days before harvesting). Estimated lowerrange 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

- 32

- 14 = 74 days (120 day variety. Cyhalofop is applied 32 days after seeding and field is drained 14 days before harvesting). Estimated Lower Range 120

- 32

- 21=67 days (120 day variety. Cyhalofop is applied 32 days after seeding and field is drained 21 days before harvesting). 2. Duration ofholding water after post-flood late (mid-season) applications EstimatedUpper 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 Lower Range 120

- 56

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

Page 9Figure 1. Growth Stages ofa Rice Variety Gown in California (Drill Seeded Variety) 

# II

L..,rsi- 1 2 J 4 5 Days: Early variety 25

- 30 Days: Lale ""(ielY 25

- 30

# 1~ Tier lnlUallon Pre-flood cyhalofop Applications Post flood applications 55-60 65-75

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

# ~1

This figure shows different growth stages ofrice after planting and stages ofcyhalofop applications. The different timing may vary depending onthe weather, location, and the rice variety.

Page 10

### Table 7. General Timeline in California Rice Production Drill (dry) Seeding 

### Cultunl**Pra~ti~e** 

## - 

## Timmi HerbicideAoolication

··- Land Preparation Early March Pre-plant treatments Mid-Marchto Mid-April Planting Third week ofApril Pre-emergence treatments Third week ofApril Flushing Inthe third week ofplanting, fields are irrigated to wet the soil and drained to facilitate seed germination. Seedling Emergence Fourth week ofApril Post-emergence pre-flood First week ofMay Cyhalofop Application treatments Permanent flooding Third week ofMay Post-flood earlytreatments Fourth week ofMay Cyhalofop application Post-flood late applications Mid-June Cyhalofop application (mid-season) 2 Draining offlooded water Mid to end ofJuly Harvesting Mid-Augustto Mid-September
1Please note that this timeline for cultural practices may vary depending on location and 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 130 day variety planted in third week ofApril.
2Pre-harvest Interval for this application is 60 days. 

### Duration ofHolding Water under Drill Seeding 1 ). Duration ofholding water in the field following the pre-permanent flood application of cyhalofop. Estimated upper range 130

- 21

- 14 

### = 95 days (130 day variety. cyhalofop is applied 21 days afterplanting and field is drained 14 days before harvesting). Estimated lowerrange 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 waterfollowing the post-flood early applications Estimatedupperrange

130

- 32 -14 

### = 84 days (130 day variety. Cyhalofop is applied 32 days after seeding and field is drained 14 days before harvesting).
Page 11Estimated lower range 130

- 32

- 21= 77 days (130 day variety. Cyhalofop is applied 32 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 CaliforniaRice Production Water 1wet) Seeding Cultural Practice 

### Timing · Herbicide Application

- '' ,( Land Preparation Early March Pre-planttreatments Mid-March to 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 Third week ofMay flood Post flood early treatments Fourth week ofMay Cyhalofop application Post-flood, late treatments Third week ofJune Cyhalofop application (mid- season) 2 Draining ofwater Second or third week ofJuly Harvesting In September
1Please 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.
2Pre-harvest interval for this application is 60 days. 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 afterplanting and field is drained 14 days before harvesting).

Page 12Estimated 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

- 32 -14 = 84 days (130 day variety. Cyhalofop is applied 32 days after seeding and field is drained 14 days before harvesting). Estimated lower range 130

- 32- 21= 77 days (130 day variety. Cyhalofop is applied 32 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. As shown in above examples, duration ofwater holding after applications ofdifferent herbicides canbe calculated for different rice varieties with known maturationtime, known herbicide application timings, and known draining timings ofwater before ha.rVesting ofthe rice crop.
REFERENCES: Arkansas Rice Production Handbook 192. Undated. Online Publication. Available at: http://www.arkansas-crops.com/wp-content/uploads/2014/02/MPl92.pdf. Accessed on June 6, 2014. Clincher® SF. Specimen Label. 2009. DowAgroSciences. Online publication Available at: http://www.cdms.net/LDat/ld5SF009.pdf. Accessed onJune 5, 2014. Crop Profiles for rice in California. 1988. Online publication. Available at: http://www.ipmcenters.org/cropprofiles/docs/carice.pdf
. Accessed onJune 9, 2014. LouisianaRice Production Handbook. 2014. Publication ofLouisiana Ag Center. Available on line at: http://www.lsuagcenter.com/NR/rdonlyres/F7E930BF-346A-45DA-A989- 37FE3DOBOF1 l/59612/pub2321RiceProdHdbkJune09.pdf. Accessed onJune 6. 2014. Page 13Proprietary Data, 2008

- 2012. Rice Background. 2008. USDA Economic Research Service. http://www.ers.usda.gov/topics/crops/rice.aspx
. Accessed ori June 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. Texas Rice Production Guidelines. 2012. Online Publication. Available at: http://varietytesting.tamu.edu/rice/varietyfiles/2012 Rice Production Guidelines.pdf Accessed on June 6, 2014.

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