UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

Date: May 27, 2015 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

SUBJECT: MCPA. Residue Chemistry Data Requirements for MCPA (2-methyl-4-chlorophenoxyacetic 

acid) use on Alfalfa and Clover. 

PCCode: 030501,030502, 030516, 030564 

Decision No.: 505072 

Petition No.: Not Applicable 

Risk Assessment Type: Not Applicable 

TXR No.: Not Applicable 

MRID No.: None 

FROM: Danette Drew, Chemist _ .......__ 

Risk Assessment Branch V 

Health Effects Division (7509P) 

Office of Pesticide Programs 

DP Barcode: 0427332 

Registration No.: Not Applicable 

Regulatory Action: Registration Review 

Case No.: 0017 

CAS No.: 94-74-6 

40 CFR: §I 80.339 

THRU: 

Michael 

Risk 

William 

Assessment 

Metzger, 

Donovan, 

Branch 

Branch 

Ph.D., 

V 

Chemifit 

Chief 

NII 

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• 

J. ~· ~ 

TO: 

Health Effects Division (7509P) 

Office of Pesticide Programs 

Khue Nguyen, CRM 

Neil Anderson, Branch Chief 

Risk Management and Implementation Branch 1 

Pesticide Re-evaluation Division (7508P) 

Office of Pesticide Programs 

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BACKGROUND

The Pesticide Re-evaluation Division (PRD) has requested that the Health Effects Division 

(HED) determine the residue chemistry data that would be required to support the use of the 

selective, post-emergence, systemic herbicide MCPA (2-methyl-4-chlorophenoxyacetic acid) on 

alfalfa and clover. There are currently two uses listed on MCPA labels that could result in 

residues on alfalfa and clover: 1) application of MCPA to small grains (barley, oats, rye, and 

wheat) that are underseeded with alfalfa or clover (or other legumes), and 2) direct application of 

MCPA to established alfalfa and clover stands.

There are adequate residue data to support the application of MCPA dimethylamine salt (DMAS) 

and MCPA 2-ethylhexyl ester (2-EHE) to small grains underseeded with alfalfa or clover. There 

are tolerances established for residues of MCPA on alfalfa forage (0.5 ppm) and hay (2.0 ppm)

based on field trial data for wheat that had been underseeded with alfalfa. There are also the 

same tolerances for residues of MCPA on the forage and hay of clover, lespedeza, trefoil, and 

vetch, based on translation from alfalfa. This translation was permitted because the MCPA Task 

Force had stated that use of MCPA on nongrass livestock feeds was to be restricted to small 

grains underseeded with alfalfa, clover, lespedeza, trefoil, and vetch. There are no outstanding 

residue data required to support the labeled use of MCPA on small grains underseeded with 

alfalfa, clover, lespedeza, trefoil, and vetch (F. Fort, D307890, 8/14/2004, MCPA: Revised 

Product and Residue Chemistry Chapters for the Reregistration Eligibility Decision).

There do not appear to be any residue data available to support the direct application of MCPA 

to alfalfa and clover stands. Direct application to alfalfa and clover could result in residues 

greater than those resulting from the application to a small grain crop covering the alfalfa and 

clover; the grain crop provides a protective canopy that could potentially decrease the amount of 

pesticide reaching the underseed crop. The current tolerances for MCPA on the forage and hay of 

alfalfa and clover may not be adequate to cover residues that may result from direct application

to those crops. The direct application uses for alfalfa and clover should be removed from the 

MCPA labels or residue data should be submitted to support those uses. 

In order to support the use of MCPA on alfalfa and clover stands, crop field trial data are needed. 

The trials should be performed according to the 860.1500 Guideline. A minimum of 12 trials for 

alfalfa and 12 trials for clover are required (for a national, not geographically restricted, use). 

Geographic location of trials should represent the distribution of the major growing areas for 

those crops. The trials should reflect the maximum application rates, minimum retreatment 

intervals, and minimum pre-harvest intervals (PHIs) on the current labels (alternatively, labels 

may be changed to reflect the field trial conditions if a different timing and rate are desired). 

Trials are required for both the of MCPA dimethylamine salt (DMAS) and MCPA 2-ethylhexyl 

ester (2-EHE) formulations. Residues of the parent MCPA compound and the metabolite 2-

HMPCA [(4-chloro-2-hydroxymethylphenoxy) acetic acid] should be determined separately and 

combined. The tolerances for MCPA on the hay and forage of alfalfa and clover will be reevaluated after receipt of acceptable residue data.

Page 2 of 3
Conclusion: There are adequate residue data to support the application of MCPA to small grains 

underseeded with alfalfa or clover. There are no residue data to support the direct application of 

MCPA to alfalfa and clover stands which could result in higher residues than applications to an 

underseeded crop. The uses for direct application to alfalfa and clover should be removed from 

the MCPA labels or crop field trial residue data should be submitted to support those uses. The 

alfalfa and clover crop field trials should be performed according to the 860.1500 Guideline.

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