UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON. D.C. 20460 

June I, 201 5 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

PC Codes: 10900 1 

MEMORANDUM DP Barcode: 425886 

SUBJECT: EPA Response to Comments Related to the "'Oxadiazon Preliminary Work Pl an: 

Registration Review·· 

AJ. _ 1 _AA~ io/1 j;)(Jt S Hannah Yingling. Biologist -Tl MU\~ · J 

Mohammed Ruhman. Ph.D .. Senior Agrono1pjst ~ 2 3. o/J/P/ I 2v /5 

Environmental Risk Branch Y 

FROM: 

Environmental Fate and Effects Division (7507P) w THROUG~1 Shamim, Branch Chief, Ph.D. !'A l/J 11.W• Jtc>1 I ( ~ ~~ ~i on ental Risk Branch Y ~· O'-

TO: 

Environmental Fate and Effects Division (7507P) 

Katherine St. Clair. Risk Manager Reviewer 

Tom Myers. Team Leader 

Risk Management and Implementation Branch 2 

Pesticide Re-Evaluation Division (7508P 

In response to the posting in the public docket or ··oxadiazon Preliminal)' Work Plan: Registration 

Review: Initial Docket. December 2014" (Docket Number EPA-HQ-OPP-20 14-0782). the registrant 

Bayer Environmental Science produced comments during the public comment period. The purpose of 

this memorandum is to address these comments. Listed below are the EPA responses. 
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1. Comment from Bayer on EPA Statement (p. 5) “Outstanding Data Requirements from GDCI109001-24733”

“For GDLN 835.4300, a new Aerobic Aquatic Metabolism study (MRID 49405201) was submitted in 

June 2014. For GDLN 850.1400, Bayer is working with the EPA to fulfill the raw data request. For 

the GDLN 850.4100, a Seedling Emergence study (MRID46676502) was submitted in 2005 and 

determined to be acceptable. For GDLN 850.4150, a Vegetative Vigor study (MRID 46676503) was 

submitted in 2005 and determined to be acceptable.”

EPA Response:

Two studies were submitted for the aerobic aquatic metabolism, the first one was under MRID 

465947-01 and was considered in the problem formulation document. In this study relatively high unextracted residues were observed. Following the issuance of the problem formulation another study 

was submitted (MRID 49405201) in which a different extraction system was used. This extraction 

system appears to be more efficient in extraction of the residues than the system used in the previous 

study. The EPA will consider the results of both studies and no longer require data related to 

oxadiazone fate in aerobic aquatic systems.

EPA acknowledges the submittal of Seedling Emergence Study (MRID 46676502) and Vegetative 

Vigor Study (MRID 46676503) classification as acceptable and no longer considers them to be 

outstanding data requirements.

2. Bayer provided General Background on Use as a comment to EPA Statement (p.4) “Anticipated 

Data Needs”

“Bayer Oxadiazon end-use products can be categorized as granular formulations or as formulations 

that are applied as liquid sprays. The granular formulations range from 0.86% to 2% active 

ingredient with and without fertilizer. The formulations that are applied as liquid sprays are a 50% 

wettable powder (WP), with and without water soluble packaging, and a liquid formulation at a 

concentration of 3.17 lb a.i./gallon. All of the Bayer oxadiazon products are labeled for application 

to turf or ornamentals.

The turf applications are predominately to golf course turf but can include application to park turf 

and commercial lawn turf. All labels expressly prohibit any application to residential turf. The 

maximum turf application rate is 4 lb a.i./A for both granular and spray applied formulations. The 

ornamental applications can be made to woody ornamental shrubs, vines and trees to control weeds. 

Applications to ornamental beds on residential property are permitted. Oxadiazon is a pre-emergent 

herbicide for the control of annual grasses and broadleaf weeds, and as such, the ornamental 

applications are ground directed for the granular applications and primarily ground directed for the 

liquid sprays. The liquid sprays do permit over the top applications to ornamentals, but require an 

immediate watering to remove foliar residues and prevent ornamental plant damage or death. “

EPA Response:

EPA will take this background information labelled use into consideration in the future risk 

assessment.
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3. Comment from Bayer on EPA Statement (p.4 ) “Anticipated Data Needs, GDLN 850.6100 

Terrestrial field dissipation study (for turf)”

“The existing laboratory study shows very little degradation (half-life of about 841 days), while 

existing field dissipation studies show significantly faster degradation (overall half-lives of 115 and 

145 days) with longer and shorter half-lives during portions of the study. These studies were 

conducted with ornamental crops in place so they are more indicative of behavior in turf rather than 

the standard bare ground field dissipation studies and clearly demonstrate that the laboratory studies 

are a conservative estimate of degradation compare to actual use conditions. Also since EPA’s 

practice is to use laboratory data in risk assessment, the conduct of a turf terrestrial dissipation study 

will not produce information that will be used in the risk assessments conducted by EPA. Based on the

existing information, Bayer will be requesting a waiver for the terrestrial field dissipation study 

conducted with turf.”

EPA Response:

EPA will look into the basis of the waiver request when submitted and respond accordingly.

4. Comment from Bayer on EPA Statement (p.4) “Anticipated Data Needs, non-GDLN Special 

Studies, Acute oral toxicity to adult and larval honeybees, Chronic toxicity to adult and larval 

honeybees.”

“Professionally managed turf is free of flowering weeds making this environment not bee attractive. 

For ornamentals, the spray and granular use is soil directed. The majority of the oxadiazon use on 

ornamentals is granular and oxadiazon is not systemic. Therefore, there is minimal exposure and 

hence minimal risk to pollinators for use on turf or ornamentals.”

EPA Response:

There are a number of weeds that may be present within a turf environment that would qualify as bee 

attractive, including but not limited to clover. Presence of flowering weeds would result in the 

presence of bees that are actively foraging. Exposure to bees with respect to a turf application cannot 

be considered minimal and risk cannot be discounted. 

5. Bayer provided the name, toxicity, structure, and CAS number for each of the degradates listed 

in Section 5 of the EFED Problem Formulation as requested (p. 8).

EPA Response:

Thank you for the information, EPA will utilize the name, toxicity, structure, and CAS for risk 

characterization in future assessments, noting that data was not provided for three degradates.

6. Comment from Bayer:
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“Typically oxadiazon is applied in the late winter/early spring for pre-emergent control of weeds. 

Applications are either made as a single sprayable application at 3-4 lb a.i/A or as a granular with 2 

applications at 2 lb a.i./A rate. Granular applications to landscape or nursery plants are made in the 

Spring or Fall. Most applications are in the South East United States. 73% of all applications were 

made in seven states: FL, NC, GA, TX, TN and AL. Timing of the first application depends on weed 

seed germination in different geographies of the US. Intervals between applications are made 30 – 60 

days for the split application in the spring (2 lb ai/A).

Further information on the applications for Bayer Labels is provided in the attached pdf. (Oxadiazon 

EFED Table 1 Use Patters Bayer Pre-lim Comment.)”

Bayer’s comment is in reference to the following excerpt from EFED Problem Formulation (p. 8 

and 9):

“Certain oxadiazon labels are unclear with respect to application parameters. Without further 

information, EPA expects to use conservative assumptions to approximate these parameters in order to 

conduct a quantitative risk assessment. However, the Agency will work with registrants to clarify 

information on oxadiazon product labels, especially the maximum annual application rates for nonagricultural uses including golf courses, turf and ornamental lawns.

Confirmation of the following label information: sites or application; formulations; application 

methods and equipment; maximum application rates; frequency of application, application intervals, 

and maximum number of applications per season; and geographic limitations on use. 

Typical application timing (date of first application and application intervals) – national, state and 

county.

The following usage/use information for non-agricultural uses: total pounds a.i. applied; percent 

crop/site treated; application rates (typical and maximum); frequency of application by region of the 

country; methods of application; target or niche pests; efficacy in formation/product performance; 

typical application interval (days).”

EPA Response:

EFED will take the expanded version of Table 1 provided by the registrant, which includes label 

clarification, into consideration in the risk assessment.