Clopyralid Summary of Analytical Chemistry and Residue Data DP#: 361787

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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF PREVENTION, PESTICIDE

AND TOXIC SUBSTANCES

MEMORANDUM

Date: 27 October 2009

SUBJECT: Clopyralid – Petition for Tolerances on Swiss chard, Bushberry Subgroup 13-

07B, and Strawberry (Regional Restriction). Summary of Analytical Chemistry

and Residue Data.

PC Code: 117401 (alkanolamine salts), 117403 

(acid)

DP Barcode: D361787

Decision No.: 403248 Registration Nos.: 62719-80, 62719-81, and 62719-84

Petition No.: 8E7481 Regulatory Action: Section 3 and 24(c) Registrations

Risk Assessment Type: NA Case No.: NA

TXR No.: NA CAS Nos.: 1702-17-6 (acid)

57754-85-5 (monoethanolamine salt)

MRID No.: See MRID Summary Table 40 CFR: 180.431 

 

FROM: Michael A. Doherty, Ph.D., Chemist

Risk Assessment Branch II

Health Effects Division (7509P)

THROUGH: William Drew, Chemist

Risk Assessment Branch II

Health Effects Division (7509P)

TO: Barbara Madden, RM 05

Risk Integration, Minor Use & Emergency Response Branch

Registration Division (7505P)

MRID Summary Table

MRID No. Study Type Comments

47604401 860.1500 Swiss chard New DER 47604401.der

47604402 860.1500 blueberry New DER 47604402.der

47604403 860.1500 strawberry New DER 47604403.der

This document was originally prepared under contract by Dynamac Corporation (1910 Sedwick 

Road, Building 100, Suite B; Durham, NC 27713). The document has been reviewed by the 

Health Effects Division (HED) and revised to reflect current Office of Pesticide Programs (OPP) 

policies.
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Executive Summary

Clopyralid [3,6-dichloro-2-pyridinecarboxylic acid] is a pyridine herbicide registered for use on 

a variety of food and feed crops in the U.S. for the postemergence control of broadleaf weeds, 

particularly thistles and clover. Permanent tolerances are established for residues of clopyralid 

in/on a wide variety of plant commodities at levels ranging from 0.5 ppm in/on stone fruits to 

500 ppm in/on grass forage and hay [40 CFR §180.431(a)], including a tolerance of 1.0 ppm for 

strawberry. Permanent tolerances are also established for residues of clopyralid in livestock 

commodities at levels ranging from 0.1 ppm in eggs to 36 ppm in meat byproducts, except liver, 

of cattle, goats, horses and sheep. There currently are no tolerances for inadvertent or indirect 

residues of clopyralid. 

The Interregional Project No. 4 (IR-4) has submitted a petition proposing the use of the 3 lb acid 

equivalent (ae)/gal emulsifiable concentrate (EC) formulation of the monoethanolamine salt of 

clopyralid (Stinger®; EPA Reg. No. 62719-73) on Swiss chard, members of the bushberry

subgroup (13-07B), and strawberries (FL and NC only). The proposed use on Swiss chard is for 

a single broadcast foliar application no later than the 8-leaf stage at 0.094-0.187 lb ae/A, and the 

proposed use on bushberries is for two soil-directed applications beginning one week after bloom 

at up to 0.25 lb ae/A/application for a maximum of 0.5 lb ae/A/season, with a minimum 

retreatment interval (RTI) of 14 days. The proposed use on strawberries is for a single broadcast 

foliar application at 0.113-0.25 lb ae/A at up to 7 days prior to harvest; this use is restricted to 

strawberries grown in FL and NC under an annual-type production system. All uses allow for 

applications using only ground equipment. The proposed minimum preharvest intervals (PHIs)

are 30 days for Swiss chard and bushberries, and 7 days for strawberries. In conjunction with the 

proposed uses on Swiss chard and bushberries, IR-4 is proposing the following permanent 

tolerances for clopyralid:

Swiss chard ..........................................................................5.0 ppm

Bushberry subgroup 13-07B................................................6.0 ppm

For the proposed use on strawberries, IR-4 is proposing the following permanent tolerance for 

clopyralid with a regional restriction:

Strawberry (annual) .............................................................4.0 ppm

Based on the available cabbage, grass, wheat and barley metabolism studies, the nature of 

clopyralid residues in plants is adequately understood for purposes of this petition. The residue 

of concern in plants for both risk assessment and the tolerance expression is clopyralid.

As the crop uses being proposed in this petition do not include any regulated livestock feedstuffs, 

issues pertaining to residues in livestock commodities are not relevant to the current petition.

An adequate gas chromatograph/electron-capture detection (GC/ECD) method (Method ACR 

75.6) is available for enforcing tolerances for clopyralid in/on plant commodities. In the 

submitted Swiss chard, blueberry and strawberry field trials, residues of clopyralid in/on each 

commodity were determined using a slightly modified version of the current enforcement 
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method. The method was adequately validated in conjunction with the analysis of field trial 

samples, and the lowest level of method validation (LLMV) was 0.05 ppm for each crop. 

The submitted Swiss chard, blueberry and strawberry field trial data are adequate and support the 

proposed uses. An adequate number of tests were conducted on each crop in the appropriate 

geographic regions at ~1x the maximum proposed rate, and the appropriate samples were 

collected from each test around the proposed PHI. Residues of clopyralid in/on each commodity 

were determined using an adequate GC/ECD method, and the duration and conditions of sample 

storage are supported by the available storage stability data. The available field trial data support 

tolerances of 3.0 ppm for Swiss chard, 0.50 ppm for the bushberry subgroup 13-07B, and 4.0 

ppm for strawberries.

No processing data are required to support the proposed uses, and the existing confined 

rotational crop study adequately supports the rotational crop restrictions specified on the current 

label.

Regulatory Recommendations and Residue Chemistry Deficiencies

Provided the label is modified to exclude use on low-growing varieties of bushberry, there are no 

deficiencies in the subject petition that would preclude establishing permanent tolerances for 

residues of clopyralid on the proposed commodities. The residue chemistry data support

tolerances for clopyralid at 3.0 ppm in/on Swiss chard and at 0.50 ppm in/on the bushberry

subgroup 13-07B, except low-bush varieties. Based on the available data, the existing tolerance 

of 1.0 ppm in/on strawberry should be increased to 4.0 ppm to support the proposed use pattern 

in FL and NC (see Table 6). HED notes that although a tolerance for the bushberry subgroup 13-

07B would include cranberry, the existing tolerance for residues in/on cranberry should remain 

due to use pattern differences between cranberry and the bushberry subgroup. HED notes that 

the recommended tolerances on bushberry and strawberry are not harmonized with Canadian 

MRLs. There are no residue chemistry considerations that would preclude granting the regional 

registrations for clopyralid. A human health risk assessment for clopyralid is forthcoming. The 

tolerance definition for clopyralid should be revised to read as follows:

Tolerances are established for residues of the herbicide clopyralid, including its 

metabolites and degradates, in or on the commodities in the table below as a result of the 

application of clopyralid. Compliance with the tolerance levels specified below is to be

determined by measuring only clopyralid [3,6-dichloro-2-pyridinecarboxylic acid] in or 

on the commodity.

Background

Clopyralid is a selective, postemergence pyridine herbicide that is used for the control of 

broadleaf weeds, particularly thistles and clover, in a variety of crops. In the current petition 

(PP#8E7481), IR-4 is proposing to expand the use of clopyralid to include applications to Swiss 

chard and bushberries for the postemergence control of various weeds. In addition, IR-4 is 

proposing a regionally restricted use on strawberries grown only in FL and NC under an annualtype production system. There is currently a use on strawberries grown as a perennial crop (DP# 

270507, 8/6/2002, D. Dotson). The chemical structure and nomenclature of the 
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monoethanolamine salt of clopyralid is summarized in Table 1, and the physicochemical 

properties of clopyralid are summarized in Table 2. 

Table1. Clopyralid Nomenclature.

Compound

N

Cl

Cl

O

O

OH

NH3

+

Common name Clopyralid, monoethanolamine salt

Company experimental name Dowco 290

IUPAC name 3,6-dichloropyridine-2-carboxylic acid, monoethanolamine salt

CAS name 3,6-dichloro-2-pyridinecarboxylic acid, monoethanolamine salt

CAS registry number 1702-17-6 (acid)

57754-85-5 (monoethanolamine salt)

End-use product (EP) 3 lb ae/gal EC (Stinger®herbicide; EPA Reg. No. 62719-73)

Table 2. Physicochemical Properties of Technical Grade Clopyralid Acid.

Parameter Value Reference

Melting point/range 149.6 Data were obtained from the 

FOOTPRINT Pesticide 

Properties DataBase, 

(http://www.eufootprint.org/ppdb.html).

pH Not available

Density (specific gravity) 1.76 g/mL

Water solubility (g/L) at 20°C 143

Solvent solubility (g/L) at 20°C Acetone – 250

Ethyl acetate – 102

Xylene – 4.6

Hexane – 6.0

Vapor pressure at 25°C, mPa 1.36

Dissociation constant, pKa, at 25°C 2.01

Octanol/water partition coefficient, Log(KOW), 

at 20°C -2.63

UV/visible absorption spectrum Not available

860.1200 Directions for Use

A 3.0 lb ae/gal EC formulation of clopyralid is currently registered to Dow AgroSciences 

(Stinger®; EPA Reg. No. 62719-73) for use on a wide variety of crops for the postemergence 

control of weeds. IR-4 is proposing new uses for this formulation on Swiss chard and members 

of the bushberry subgroup. Although there is an existing use for clopyralid on perennial 

strawberries, with a 30-day PHI, IR-4 is also proposing to establish a new use for strawberries 

grown under an annual production system in the states of NC and FL. Examples of supplemental 

labels for the 3 lb ae/gal EC were provided, and the proposed use directions are summarized 

below in Table 3.
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Table 3. Summary of Directions for Use of Clopyralid.

Applic. Timing, Type, and 

Equip. 1

Formulation

[EPA Reg. No.]

Applic. Rate 

(lb ae/A)

Max. No. 

Applic. per 

Season

Max. Seasonal 

Applic. Rate

(lb ae/A)

PHI

(days)

Use Directions and 

Limitations 2

Swiss Chard

Broadcast foliar application 

when crop is at the cotyledon 

to 8-leaf stage of growth; 

ground equipment.

3.0 lb ae/gal EC 

[62719-73] 0.094-0.187 1 0.187 30 Apply in a minimum of 10 gal/A

Bushberry subgroup 13-07B

Directed applications to row 

middles beginning 1 week 

after bloom; ground 

equipment 

3.0 lb ae/gal EC 

[62719-73] 0.06-0.25 2 0.5 30

Apply in a minimum of 10 

gal/A, with a minimum 

RTI of 14 days. Do not 

apply by aircraft.

Strawberry (annual fields only in FL and NC)

Broadcast foliar application 

to well-established plantings; 

ground equipment

3.0 lb ae/gal EC 

[62719-73] 0.113-0.25 1 0.25 7

Apply in a minimum of 20 

gal/A. Do not use with a 

surfactant.

Do not apply by aircraft

1 Do not apply through any type of irrigation system.

2 The label for the 3 lb ae/gal EC contains the following rotational crop restrictions: barley, canola, cole crops, flax, garden 

beets, grasses, corn (field, pop and sweet), oats, spinach, sugar beets, turnips and wheat may be planted at anytime following a 

treated crop. Depending on the amount of soil organic matter, rainfall and location (state), the plant-back intervals for all other 

crops range from 10.5 to 18 months.

Conclusions. The labels are adequate to allow evaluation of the residue data relative to the 

proposed uses. The available field trial data support the proposed use directions, although the 

label should be revised to exclude use on low-growing varieties of bushberry. 

860.1300 Nature of the Residue - Plants

DP# 270507, 8/6/2002, D. Dotson

The nature of the residue in plants is adequately understood for purposes of this petition based on

the acceptable cabbage, grass, barley and wheat metabolism studies. In each of these studies, the 

major 14C-residue was determined to be only parent compound. Although data are available for 

only two dissimilar crops (leafy vegetable and cereal grain), HED has concluded that the residue 

of concern in plants for purposes of this petition is clopyralid. However, the Agency reserves the 

right to require additional metabolism studies in the future should the petitioner request the 

establishment of clopyralid tolerances for additional crops. 

860.1300 Nature of the Residue - Livestock

There are no livestock feedstuffs associated with the proposed use on Swiss chard, bushberry

subgroup 13-07B, and strawberry. Therefore, data requirements for livestock metabolism are not 

relevant to this tolerance petition.

860.1340 Residue Analytical Methods
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Enforcement method. The Pesticide Analytical Manual (PAM) Vol. II lists a GC/ECD method 

for determining residues of clopyralid residues in/on plant commodities (Method I or Method 

ACR 75.6).

For this method, residues are extracted with dilute NaOH (0.25% or 0.1%) and filtered. The 

extract is then acidified and salinized, and residues are partitioned into ethyl ether. Residues are 

then methylated using diazomethane and cleaned up on an activated Alumina column. Residues 

are then determined by GC/ECD using external standards. The reported LOQs are 0.5 ppm for 

grains and 2.0 ppm for green forage.

Data collection methods. In the submitted field trials, residues of clopyralid in/on samples of 

Swiss chard, blueberries and strawberries were determined using a slightly modified version of 

the current tolerance enforcement method.

For each commodity, residues were extracted with 0.5% NaOH and centrifuged. The resulting 

extract was acidified with HCl and salinized with NaCl, and residues were partitioned into ethyl 

ether. Residues were then methylated using diazomethane, concentrated to dryness, re-dissolved 

in toluene, and cleaned up using an activated Alumina A column eluted with toluene. The 

methylated residues were analyzed by GC/ECD using external standards. Residues are 

expressed in terms of parent clopyralid using a conversion factor of 0.93. The lowest level of 

method validation (LLMV) for clopyralid in each commodity was 0.05 ppm. The calculated 

LOQs were 0.052-0.073 ppm and the LODs were 0.017-0.024 ppm.

The above method was adequately validated using control samples of each matrix fortified with 

clopyralid at 0.05-5.0 ppm. Acceptable recoveries were obtained for each matrix, and the 

fortification levels bracketed the measured residue levels. Apparent residues of clopyralid were 

<LOQ in/on control samples, which the exception of two control samples from one of the 

blueberry field trials which had apparent residues of clopyralid at 0.060 and 0.055 ppm.

Conclusions. An adequate GC/ECD method (Method ACR 75.6) is available for enforcing the 

proposed tolerances and collecting data on residues of clopyralid in Swiss chard, blueberries and 

strawberries.

860.1360 Multiresidue Methods

The FDA Pestrak database (PAM Vol. I, Appendix dated 11/6/90) indicates that the existing 

FDA multiresidue methods are not likely to recover clopyralid. HED notes that clopyralid does 

appear to be adequately recovered by the “QuEChERS” multiresidue method 

(http://www.quechers.com).

860.1380 Storage Stability

DP# 270507, 8/6/2002, D. Dotson

Under frozen storage conditions, clopyralid has been shown to be stable in plant commodities for 

the following durations: 50 months in safflower seeds, soybeans, sugar beet roots and tops, and 

oat forage, grain and straw; 30 months in strawberries; 26 months in dried hops cones; 16 
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months in cherries and plums; 15 months in canola meal; 10 months in canola seed and oil; 9 

months in cabbage and spinach; 5 months in mustard greens; and 3 months in peaches.

Samples collected from the submitted field trials were stored frozen within 3 hours after harvest, 

shipped frozen to the analytical laboratory 2-40 days later, and stored at -21°C at the analytical 

laboratory until analysis. The maximum frozen storage intervals, from harvest to analysis of 

samples, are listed in Table 4.

Table 4. Summary of Storage Conditions and Durations of Samples from Crop Field Trial Studies. 

Matrix Storage 

Temperature (°C)

Actual Storage Duration

(days)

Interval of Demonstrated Storage 

Stability (months)

Swiss Chard -21 ± 7 41-91 5 (Mustard Greens)

Blueberry -21 ± 7 41-132 16 (Cherry)

Strawberry -21 ± 7 90-99 30 (Strawberry)

Conclusions. Adequate storage stability data are available to support the sample storage 

conditions and durations in the submitted field trials.

860.1400 Water, Fish, and Irrigated Crops

There are no proposed uses that are relevant to this guideline topic.

860.1460 Food Handling

There are no proposed uses that are relevant to this guideline topic.

860.1480 Meat, Milk, Poultry, and Eggs

There are no livestock feedstuffs associated with the proposed use on Swiss chard, bushberry

subgroup 13-07B and strawberry. Therefore, data requirements pertaining to meat, milk, 

poultry, and eggs are not relevant to this tolerance petition.

860.1500 Crop Field Trials

47604401.der (Swiss Chard)

47604402.der (blueberry)

47604403.der (strawberry)

IR-4 has submitted new field trial data supporting the proposed uses of clopyralid (3 lb ae/gal 

EC) on Swiss chard and members of the bushberry subgroup 13-07B. Although there is an 

existing use for clopyralid on strawberries grown under a perennial cropping system, IR-4 is 

requesting a new use on strawberries grown in FL and NC under an annual production system. 

New strawberry field trial data have been submitted to support this new use. The results from 

these field trials are discussed below and the residue data are summarized in Table 5.
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Table 5. Summary of Residue Data from Crop Field Trials with Clopyralid (EC).

Crop matrix Total Applic. 

Rate (lb ae/A)

PHI 

(days)

Residue Levels (ppm) 1

n Min. Max. HAFT 1 Median Mean Std. Dev.

Swiss Chard (proposed use = 0.187 lb ae/A total application rate, 30-day PHI)

Swiss Chard

0.093-0.103

28-29

8 0.05 0.70 0.62 0.34 0.34 0.22

0.188-0.199 8 <0.05 1.90 1.60 0.57 0.69 0.69

Bushberry subgroup 13-07B (proposed use = 0.5 lb ae/A total application rate, 30-day PHI)

Blueberry 30.483-0.525 27-33 14 <0.05 0.42 0.38 0.06 0.12 0.12

Strawberry, grown in FL and NC only (proposed use = 0.25 lb ae/A total application rate, 7-day PHI)

Strawberry

0.119-0.125

7-8

6 0.79 1.80 1.70 0.98 1.18 0.42

0.246-0.255 6 1.60 3.00 2.85 2.40 2.35 0.53

1 Residues are expressed in terms for clopyralid acid. The LLMV for clopyralid was 0.05 ppm. For all 

calculations, 0.05 ppm was used for any residue values <LLMV.

2 HAFT = Highest Average Field Trial.

3

 Residues from the field trial in ME, which used a foliar application, have not been included in the summary of 

residue data.

Swiss Chard. Four field trials were conducted on Swiss chard in Zones 1, 2 and 11 during the 

2002 growing season. In side-by-side tests at each site, the monoethanolamine salt of clopyralid 

(3.0 lb ae/gal EC) was applied to Swiss chard as a single broadcast foliar application during 

vegetative development at rates of 0.093-0.103 lb ae/A or 0.188-0199 lb ae/A (0.5 and 1.0x the 

proposed rate). Applications were made using ground equipment in volumes of 16-60 gal/A, 

without the use of a spray adjuvant. Single control and duplicate treated samples of Swiss chard 

(leaves and petioles) were harvested from each plot at commercial maturity, 28-29 days after 

treatment (DAT). 

Samples were stored at ≤-21°C for up to 3 months from harvest to analysis; a duration that is 

supported by the available storage stability data. Samples were analyzed for residues of 

clopyralid using an adequate GC/ECD method, which is a slightly modified version of the 

current tolerance enforcement method (Method ACR 79.5). The lowest level of method LLMV 

for clopyralid in Swiss chard was 0.05 ppm.

Following a single broadcast foliar application of clopyralid (EC), residues in/on Swiss chard 

harvested at 28-29 DAT were 0.05-0.70 ppm at the 0.5x rate and <0.05-1.90 ppm at the 1x rate. 

For the 0.5x and 1x use rates, average residues were 0.34 and 0.69 ppm, respectively, and the 

HAFT residues were 0.62 and 1.60 ppm. A residue decline study was not conducted.

Bushberry Subgroup 13-07. Nine blueberry field trials were conducted in Zones 1, 2, 5 and 12 

during the 1999 and 2000 growing seasons. Lowbush type blueberries were treated at the one 

test site in ME (Zone 1), and highbush type blueberries were treated at all the other test sites. At 

each site, the monoethanolamine salt of clopyralid (3 lb ae/gal) was applied to blueberries as two 

applications during early fruit development at rates of 0.240-0.264 lb ae/A, for a total rate of 

0.490-0.525 lb ae/A/season (1x proposed rate). For the lowbush blueberry test, the two 

applications were made as broadcast foliar applications. For the highbush blueberry tests, the 

two applications were made as directed applications to the ground between the crop rows, 

avoiding contact with the bushes. Applications were made at RTIs of 12-21 using ground 
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equipment in volumes of 20-31 gal/A, without the use of a spray adjuvant. Single control and 

duplicate treated samples were harvested from each site at commercial maturity, 27-33 DAT.

Samples were stored at ≤-21°C for up to 4.3 months from harvest to analysis; an interval that is 

supported by the available storage stability data. Samples were analyzed for residues of 

clopyralid using an adequate GC/ECD method, which is a slightly modified version of the 

current tolerance enforcement method (Method ACR 79.5). The LLMV for clopyralid in 

blueberries was 0.05 ppm.

The residue data from one of the tests (Trial MI16) were excluded from the dataset because 

clopyralid residues were found in controls samples at levels similar to the residue levels in the

associated treated samples. These data were not used in determining a recommended tolerance 

level (see Appendix II).

Following two broadcast foliar application of clopyralid (EC) totaling 0.49 lb ae/A, residues

were 4.7 and 5.8 ppm in/on blueberries harvested at 28 DAT. Following soil-directed 

application at rates ranging from 0.48 to 0.53 lb ae/A, residues were <0.05 – 0.42 ppm in/on 

blueberries harvested 27-33 DAT. Not including the foliar treatment, the average residue was

0.11 pm and the highest average field trail (HAFT) residue was 0.38 ppm. A residue decline 

study was not conducted.

Strawberry (annual production system in FL and NC only). Three field trials were 

conducted in Zones 2 and 3 during the 2002 growing season on strawberries growing in an 

annual-type production system. In side-by-side tests at each site, the monoethanolamine salt of 

clopyralid (3.0 lb ae/gal EC) was applied to strawberries as a single broadcast foliar application 

during fruiting at rates of 0.119-0.125 lb ae/A or 0.246-0.255 lb ae/A (0.5x and 1x the proposed 

use rate). Applications were made using ground equipment in volumes of 29-35 gal/A, without 

the use of a spray adjuvant. Single control and duplicate treated samples of strawberries were 

harvested from each plot at commercial maturity, 7-8 DAT.

Samples were stored at ≤-21°C for up to 3 months from harvest to analysis; a duration that is 

supported by the available storage stability data. Samples were analyzed for residues of 

clopyralid using an adequate GC/ECD method, which is a slightly modified version of the 

current tolerance enforcement method (Method ACR 79.5). The LLMV for clopyralid in 

strawberries was 0.05 ppm.

Following a single broadcast foliar application of clopyralid (EC), residues in/on strawberries 

harvested at 7-8 DAT were 0.079-0.180 ppm at the 0.5x rate and 1.60-3.00 ppm at the 1x rate. 

For the 0.5x and 1x rates, average residues were 1.18 and 2.35 ppm, respectively, and the HAFT 

residues were 1.70 and 2.85 ppm. A residue decline study was not conducted. 

Conclusions. The Swiss chard, blueberry and strawberry field trials are adequate and support the 

proposed use patterns. An adequate number of tests were conducted in the appropriate 

geographical regions, and samples were analyzed for the residue of concern using an adequate 

data collection method. Adequate storage stability data are available to support the storage 

conditions incurred in the field trials. The data support tolerances of 3.0 ppm in/on Swiss chard 
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and 0.50 ppm in/on bushberries, provided low-growing varieties are excluded. The data also 

support a 4.0 ppm in/on strawberries, with a regional restriction to FL and NC. The label should 

be revised to prohibit use on low-growing varieties of bushberries since their morphology does 

not readily allow for soil applications. Furthermore, directions for a previously established use 

on cranberry (a member of the bushberry group) are significantly different than the currently 

proposed use; therefore, the existing tolerance for cranberry should remain even if a tolerance for 

the bushberry subgroup is established.

860.1520 Processed Food and Feed

HED does not require residue data for any processed commodities associated with Swiss chard, 

bushberry subgroup 13-07B, and strawberry. Therefore, data requirements for processed food 

and feed are not relevant to this tolerance petition.

860.1650 Submittal of Analytical Reference Standards

An analytical standard for clopyralid is currently available in the EPA National Pesticide 

Standards Repository (personal communication with Dallas Wright, ACB, 6/12/2009). 

860.1850/1900 Confined and Field Accumulation in Rotational Crops

DP# 193219, 8/4/93, G. Kramer

An acceptable confined rotational crop study is available for clopyralid. In this study, the total 

radioactive residues in/on representative rotational crop commodities (lettuce, turnips, green 

beans, and wheat) were below 0.01 ppm at plant-back intervals of 49-98 days following 

application of [14C]clopyralid to the soil at 0.29 lb ae/A (1.17x the maximum seasonal rate for 

crops which can be rotated).

 

The current label for the 3 lb ae/gal EC of clopyralid allows for the replanting of the following 

crops at anytime: barley, canola, cole crops, flax, garden beets, grasses, corn (field, pop and 

sweet), oats, spinach, sugar beets, turnips and wheat. The plant-back interval for all other crops 

is 10.5 to 18 months depending on the amount of soil organic matter, rainfall and location (state).

The established rotational crop restrictions are adequate. Limited field rotational crop studies are 

not required, and no tolerances are required for inadvertent or indirect residues in rotational 

crops.

860.1550 Proposed Tolerances

Permanent tolerances are established for residues of clopyralid in/on a wide variety of plant 

commodities at levels ranging from 0.5 ppm in/on stone fruits to 500 ppm in/on grass forage and 

hay [40 CFR §180.431(a)], including a 4.0 ppm tolerance on cranberry, which is a member of the 

bushberry subgroup 13-07B, and a 1.0 ppm tolerance on strawberry. Permanent tolerances are 

also established for residues of clopyralid per se in livestock commodities at levels ranging from 

0.1 ppm in eggs to 36 ppm in meat byproducts, except liver, of cattle, goats, horses and sheep. 
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Currently there are no tolerances for inadvertent or indirect residues of clopyralid. A summary

of the recommended tolerances for the petition are listed in Table 6.

An adequate number of field trials at ~1x the proposed use rate are available for Swiss chard and 

blueberries to support permanent tolerances on Swiss chard and the bushberry subgroup 13-07B 

(except low-growing varieties), of which blueberry is the representative crop. An adequate 

number of strawberry field trials were also conducted in Zones 2 and 3 at 1x the proposed use 

rate to support a tolerance with a regional restriction to NC and FL. The Agency’s SOP 

“Guidelines for Setting Pesticide Tolerances Based on Field Trial Data” were utilized for 

determining the appropriate tolerance level for each commodity (Appendix II). The 

recommended tolerances on Swiss chard and the bushberry subgroup 13-07B (except lowgrowing varieties) are 3.0 and 0.50 ppm, respectively. On strawberries, the new use pattern 

results in a recommended tolerance of 4.0 ppm. As previously noted, the current tolerance for 

cranberry at 4.0 ppm should remain even if tolerances for the bushberry subgroup are 

established.

There are no Codex or Mexican maximum residue limits (MRLs) for residues of clopyralid in/on 

the requested commodities (Appendix I). However, there are Canadian MRLs for residues of 

clopyralid at 1.0 mg/kg on strawberry and 0.1 mg/kg on blueberry. The Canadian MRL for 

strawberry harmonizes with the existing tolerance on strawberry. Based on the proposed use on 

strawberry and bushberries, and the available residue data, the recommended tolerances on 

strawberry and bushberries (subgroup 13-07B) cannot be harmonized with the Canadian MRLs.

Table 6. Tolerance Summary for Clopyralid.

Commodity Proposed/Existing

Tolerance (ppm)

Recommended 

Tolerance (ppm)

Comments; Correct Commodity 

Definition

40 CFR §180.431(a)

Swiss Chard 5.0 3.0 Adequate field trail data are available.

Bushberry subgroup 13-07B 6.0 0.50 Adequate field trail data are available; 

however, the tolerance should be for the 

subgroup except low-growing 

varieties.

Cranberry 4.0 4.0 The tolerance on cranberries should 

remain due to differences in use pattern 

and residue level versus the currently 

proposed use on bushberry

Strawberry 4.0 4.0 Adequate field trial data are available to 

support a 7-day PHI on strawberries 

grown under an annual-type production 

system in FL and NC only. This 

tolerance will supersede the existing 

1.0-ppm tolerance already established 

on strawberry (grown under a perennial 

production system).
Clopyralid Summary of Analytical Chemistry and Residue Data DP#: 361787

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References

DP Number: 193219

Subject: ID# 062719-00073. Review of Confined Rotational Study of Clopyralid.

From: G. Kramer

To: J. Miller

Date: 8/4/93

MRID: 42815001

DP Number: D270507

Subject: Clopyralid. Review of Residue Chemistry Data in Support of Permanent or 

Time-Limited Tolerances Proposed for Canola (PP#1E6291), Cherries 

(PP#1E6329), Crambe (PP#1E6291), Cranberry (PP#1E6340), Flax 

(PP#1E6227), Garden Beets (PP#1E6333), Head and Stem Brassica 

(PP#1E6999), Hops (PP#1E6283), Mustard Greens (PP#1E6334), Peaches 

(PP#1E6329), Plums (PP#1E6329), Spinach (PP#1E6320), Strawberries 

(PP#1E6241), Sweet Corn (PP#4F4379), Popcorn (PP#4F4379), and Turnips 

(PP#1E6335).

From: Douglas A. Dotson

To: S. Brothers/R. Forrest

Date: 8/6/2002

MRID: 41904401, 41904402, 41904403, 44212601, 45036101, 45259901, 

45372801, 45372802, 45390001, 45419801, 45436901, 45436902, 45436903, 

45446901, 45447001, 45447101, 45473601, and IR-4 Rpt No. PR 07223

Attachments: 

Appendix I - International Residue Limit Status sheet

Appendix II - Tolerance Assessment Calculations
Clopyralid Summary of Analytical Chemistry and Residue Data DP#: 361787

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Appendix I. International Residue Limit Status Sheet

INTERNATIONAL RESIDUE LIMIT STATUS

Chemical Name: 

3,6-dichloro-2-

pyridinecarboxylic acid

Common Name: 

Clopyralid

X Recommended tolerances

⁯ Reevaluated tolerance

⁯ Other

Date: 07/20/09

Codex Status (Maximum Residue Limits) U. S. Tolerances

√ No Codex proposal step 6 or above

⁯No Codex proposal step 6 or above for the crops 

requested

Petition Number: PP# 8E7481

DP #s: 361787

Other Identifier: 

Residue definition (step 8/CXL): NA Reviewer/Branch: M. Doherty, HED/RAB2

Residue definition: Clopyralid

Crop (s) MRL (mg/kg) Crop(s) Tolerance (ppm)

Bushberry, subgroup 13-07B 0.5

Strawberry 4.0

Swiss chard 3.0

Limits for Canada Limits for Mexico

⁯ No Limits

⁯ No Limits for the crops requested

⁯ No Limits

√ No Limits for the crops requested

Residue definition: Clopyralid Residue definition: NA

Crop(s) MRL (mg/kg) Crop(s) MRL (mg/kg)

Blueberry 0.1

Strawberry 1.0

Notes/Special Instructions: 
Clopyralid Summary of Analytical Chemistry and Residue Data DP#: 361787

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Appendix II. Tolerance Assessment Calculations.

For each of the crops listed below, the Guidance for Setting Pesticide Tolerances Based on Field 

Trial Data (SOP), along with the tolerance spreadsheet, was used for calculating recommended 

tolerances. As specified in the SOP, the minimum of the 95% upper confidence limit (UCL) on 

the 95th percentile and the point estimate of the 99th percentile was selected as the tolerance value 

in cases when the dataset was large (greater than 15 samples) and reasonably lognormal. For 

datasets that were small (≤15 samples) and reasonably lognormal, the upper bound estimate of 

the 95th percentile based on the median residue value was compared to the minimum of the 95% 

UCL on the 95th percentile and the point estimate of the 99th percentile, and the minimum value 

was selected as the tolerance value. For datasets that were not lognormal, the upper bound on 

the 89th percentile was selected as the tolerance value (distribution-free method). The rounding

procedures specified in the SOP were also used.

Swiss chard. The dataset used to establish a tolerance for clopyralid on Swiss chard consisted of 

field trial data representing a single application at rates of 0.19-0.20 lb ae/A with a 28-29-day

PHI. As specified by the SOP, the field trial application rates and PHIs are within 25% of the 

maximum label application rate and minimum label PHI, respectively. The residue values used 

to calculate the tolerance are provided in Table II-1.

All but 2 field trial sample results for Swiss chard were above the LOQ (0.05 ppm). The Swiss 

chard dataset was small (8 samples). The dataset was entered into the tolerance spreadsheet. 

Although the result from the approximate Shapiro-Francia test statistic (Figure I-2) indicated that 

the assumption of lognormality should not be rejected, visual inspection of the lognormal 

probability plot (Figure II-1) provided in the spreadsheet indicated that the dataset was not 

reasonably lognormal. Using the tolerance spreadsheet, the recommended tolerance is 3.0 ppm 

on Swiss chard.

Table II-1. Residue data used to calculate tolerance for Clopyralid on Swiss Chard.

Regulator: EPA

Chemical: Clopyralid

Crop: Swiss Chard

PHI: 28-29 days

App. Rate: 1 application at 0.19-0.20 lb ae/A

Submitter: IR-4

MRID Citation: MRID 47604401

Residues

0.05

0.05

0.12

0.21

0.92

0.99

1.3

1.9
Clopyralid Summary of Analytical Chemistry and Residue Data DP#: 361787

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Figure II- 1. Lognormal probability plot of Clopyralid field trial data for Swiss chard.

Lognormal Probability Plot

0.1 1 2 5 10 20 30 50 70 80 90 95 98 99 99.9

2.0000

1.0000

0.5000

0.2500

0.1250

0.0625

0.0313

y = 1.5208x - 1.1077

R

2

 = 0.9014

Percentiles

Concentrations

EPA Clopyralid Swiss Chard 28-29 days 1 at 0.188-0.199 lb ai/A IR-4 MRID 47604401

Figure II- 2. Tolerance spreadsheet summary of Clopyralid field trial data for Swiss Chard.

Regulator: EPA

Chemical: Clopyralid

Crop: Swiss Chard

PHI: 28-29 days

App. Rate1 :at 0.188-0.199 lb ai/A

Submitter: IR-4

MRID Citation: MRID 47604401

n: 8

min: 0.05

max: 1.90

median; 0.57

average: 0.69

95th Percentile 99th Percentile 99.9th Percentile

1.9 2.5 3.0

(3.0) (4.0) (--)

4.0 11 35

(40) (220) (--)

2.5

3.0

UPLMedian95th 6.0

0.9014

p-value > 0.05 : Do not reject lognormality assumption

Y

EU Method I

Normal

EU Method I

Log Normal

Would you like the above values 

rounded? (Y or N)==>

Approximate 

Shapiro-Francia 

Normality Test 

EU Method II

Distribution-Free

California Method

μ + 3σ
Clopyralid Summary of Analytical Chemistry and Residue Data DP#: 361787

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Bushberry subgroup 13-07B.

The dataset used to establish a tolerance for clopyralid on the bushberry subgroup 13-07B 

consisted of field trial data on blueberries at application rates of 0.483-0.525 lb ae/A (2 

applications at 0.240-0.264 lb ae/A) with a 27-33 day PHI. As specified by the SOP, the field 

trial application rates and PHIs are within 25% of the maximum label application rate and 

minimum label PHI, respectively. The residue values used to calculate the tolerance are 

provided in Table II-2. Residues from the foliar application trial are not included in the dataset.

The blueberry dataset is relatively large (14 samples). The dataset was entered into the tolerance 

spreadsheet. The approximate Shapiro-Francia test statistic (Figure II-4) indicates that the 

assumption of lognormality should be rejected and visual inspection of the lognormal probability

plot for blueberry (Figure II-3) provided in the spreadsheet supports that conclusion. Therefore, 

the recommended tolerance on the bushberry subgroup 13-07B is 0.50 ppm.

Table II-2. Residue data used to calculate tolerance for Clopyralid on Blueberry.

Regulator: EPA

Chemical: Clopyralid

Crop: Blueberry

PHI: 27-33 Days

App. Rate: 2 applications at 0.240-0.264 lb ae/A

Submitter: IR-4

MRID Citation: MRID 47604402

Residues

0.05

0.05

0.05

0.05

0.05

0.05

0.056

0.057

0.064

0.095

0.16

0.22

0.34

0.42
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Figure II- 3. Lognormal probability plot of Clopyralid field trial data for Blueberry.

Lognormal Probability Plot

0.1 1 2 5 10 20 30 50 70 80 90 95 98 99 99.9

1.0000

0.5000

0.2500

0.1250

0.0625

0.0313

y = 0.7123x - 2.4369

R

2

 = 0.7594

Percentiles

Concentrations

EPA Clopyralid Blueberry 27-33

Figure II- 4. Tolerance spreadsheet summary of Clopyralid field trial data for Blueberry.

Regulator: EPA

Chemical: Clopyralid

Crop: Blueberry

PHI: 27-33

App. Rate:

Submitter:

n: 14

min: 0.05

max: 0.42

median: 0.06

average: 0.12

95th Percentile 99th Percentile 99.9th Percentile

0.35 0.45 0.50

(0.45) (0.60) (--)

0.35 0.60 1.0

(0.70) (1.5) (--)

0.35

0.50

0.35

0.7594

p-value <= 0.01: Reject lognormality assumption

Would you like the above values rounded? (Y or N)==> Y

Approximate

Shapiro-Francia

Normality Test 

EU Method I

Normal

UCLMedian95th

95/99 Rule

EU Method II

Distribution-Free

Mean+3SD
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Strawberry (grown in an annual production strategy; FL and NC only)

The dataset used to establish a tolerance for clopyralid on strawberry consisted of field trial data 

representing a single application at rates of 0.246-0.255 lb ae/A with a 7-8 day PHI. As specified 

by the SOP, the field trial application rates and PHIs are within 25% of the maximum label 

application rate and minimum label PHI, respectively. The residue values used to calculate the 

tolerance are provided in Table II-3.

All field trial sample results for strawberry were above the LOQ (0.05 ppm). The strawberry

dataset was small (6 samples). The dataset was entered into the tolerance spreadsheet. Visual 

inspection of the lognormal probability plot for strawberry (FigureII-5) provided in the 

spreadsheet indicated that the dataset was reasonably lognormal. The result from the 

approximate Shapiro-Francia test statistic (Figure II-6) confirmed that the assumption of 

lognormality should not be rejected for strawberry. Using the tolerance spreadsheet, the 

recommended tolerance is 4.0 ppm on strawberries.

Table II-3. Residue data used to calculate tolerance for Clopyralid on Strawberry.

Regulator: EPA

Chemical: Clopyralid

Crop: Strawberry (annual, grown only in FL)

PHI: 7-8 Days

App. Rate: 1 application at 0.246-0.255 lb ae/A

Submitter: IR-4

MRID Citation: MRID 47604403

Residues

1.6

2.0

2.1

2.7

2.7

3.0
Clopyralid Summary of Analytical Chemistry and Residue Data DP#: 361787

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Figure II- 5. Lognormal probability plot of Clopyralid field trial data for Strawberry.

Lognormal Probability Plot

0.1 1 2 5 10 20 30 50 70 80 90 95 98 99 99.9

3.0000

1.5000

y = 0.2502x + 0.8317

R

2

 = 0.9327

Percentiles

Concentrations

EPA Clopyralid Strawberry 7-8 Days 1 at 0.246-0.255 lb ai/A IR-4 MRID 47604403

Figure II- 6. Tolerance spreadsheet summary of Clopyralid field trial data for Strawberry.

Regulator: EPA

Chemical: Clopyralid

Crop: Strawberry

PHI: 7-8 Days

App. Rate1 :at 0.246-0.255 lb ai/A

Submitter: IR-4

MRID Citation: MRID 47604403

n: 6

min: 1.60

max: 3.00

median; 2.40

average: 2.35

95th Percentile 99th Percentile 99.9th Percentile

3.5 4.0 4.0

(4.5) (6.0) (--)

3.5 4.0 5.0

(6.0) (8.0) (--)

6.0

4.0

UPLMedian95th 30

0.9327

p-value > 0.05 : Do not reject lognormality assumption

Y

EU Method I

Normal

EU Method I

Log Normal

Would you like the above values 

rounded? (Y or N)==>

Approximate 

Shapiro-Francia 

Normality Test 

EU Method II

Distribution-Free

California Method

μ + 3σ