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INTRODUCTION

This is the Environmental Protection Agency’s (EPA or the Agency) Final Work Plan (FWP) for the 

registration review of dikegulac sodium. This work plan addresses public comments received 

concerning the Preliminary Work Plan (PWP), which was posted in the dikegulac sodium 

registration review docket (EPA-HQ-OPP-2014-0771). Dikegulac-sodium is a plant growth 

regulator that was first registered in 1978. It is registered for use on ornamentals, nursery crops, and 

trees to reduce growth, flowering, and/or fruit set. There are residential uses of dikegulac sodium. 

Three end-use products containing dikegulac-sodium are currently registered for use in the United 

States. Dikegulac-sodium was previously assessed at the time of the development of the 

Reregistration Eligibility Decision (RED) in 2007. 

The Agency is implementing the registration review program pursuant to Section 3(g) of the Federal 

Insecticide, Fungicide, and Rodenticide Act (FIFRA), and will review each registered pesticide every 

15 years to determine whether it continues to meet the FIFRA standard for registration. Changes in 

science, public policy, and pesticide use practices occur over time. The registration review program 

is intended to make sure that, as the ability to assess risk evolves and as policies and practices 

change, all registered pesticides continue to meet the statutory standard. The public phase of 

registration review begins when the initial docket is opened for each case. Information on this 

program is provided on the Agency’s website.

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The FWP begins with any updates since the PWP was issued. Next is a summary of substantive 

comments received during the public comment period for the PWP concerning anticipated data 

needs, expected risk assessments, or the estimated timeline identified in the PWP, and a summary of

the Agency’s responses to those comments. This section is followed by registration review planned 

data needs, risk assessments expected to be conducted, and the projected registration review timeline

for dikegulac sodium. Lastly, there is a discussion of next steps.

UPDATES SINCE THE PWP WAS ISSUED

There are no additional updates on dikegulac sodium since the PWP.

SUMMARY OF COMMENTS AND AGENCY RESPONSES

During the 60-day public comment period on the Dikegulac Sodium Preliminary Work Plan, which 

opened on December 19, 2014 and closed on February 19, 2015, the Agency received two public 

comments. Comments were submitted by the FIFRA Endangered Species Task Force (FESTF) and The 

Center for Biological Diversity (CBD). The comments do not address the timeline described in the PWP, 

but they do address the planned ecological and human health risk assessments and data 

requirements. In the PWP, EPA also solicited comments on the specific topics of environmental 

justice, water quality concerns, and trade irritants, but no comments or information were received on 

those issues.

Summarized below are public comments received in response to the Dikegulac Sodium Preliminary 

Work Plan. Public comments in their entirety are located in the docket, EPA-HQ-OPP-2014-0771.

 

1 http://www.epa.gov/oppsrrd1/registration_review/
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Comments submitted by the FIFRA Endangered Species Task Force (FESTF) in EPA-HQOPP-2014-0771-0007

Comment: FESTF submitted a comment informing the Agency that the technical registrant of dikegulac sodium,

PBI/Gordon Corporation, is a member of the FESTF (or a company having met its data compensation obligations) 

and is entitled to rely on FESTF data.

Response: The Agency thanks FESTF for its comment.

Comments submitted by the Center for Biological Diversity (CBD) in EPA-HQ-OPP-2014-

0771-0006

Comment: The Center for Biological Diversity’s (CBD) comments focus on the EPA’s duty to consult with the U.S. 

Fish and Wildlife Service and the National Marine Fisheries Service (the Services) on the registration review of 

dikegulac sodium in accordance with the Endangered Species Act (ESA). The CBD comments mention various 

aspects of the risk assessment process, including use of the best available data to develop endangered species risk 

assessments, and evaluation of effects on endangered and threatened species and their designated critical habitat. CBD 

also expresses concern regarding the rigor of the Agency’s preliminary determinations regarding the effects of dikegulac 

sodium on endangered and threatened (listed) species and their designated critical habitat for the dikegulac sodium 

registration review. 

 

Response: EPA has reviewed the comments from CBD on the registration review docket opening 

for dikegulac sodium and plans to address many of the concerns raised by CBD as part of the 

implementation plan for assessing the risks of pesticides to listed species based on the 

recommendations of the April 2013 National Academy of Sciences (NAS) report. EPA will address 

concerns specific to dikegulac sodium in connection with the development of its final registration 

review decision for dikegulac sodium.

In November 2013, the EPA, along with the Services and the USDA, released a summary of their 

joint Interim Approaches for assessing risks to endangered and threatened (listed) species from 

pesticides. The Interim Approaches were developed jointly by the agencies in response to the 

National Academy of Sciences’ (NAS) recommendations and reflect a common approach to risk 

assessment shared by the agencies as a way of addressing scientific differences between the EPA and 

the Services. The NAS report outlines recommendations on specific scientific and technical issues 

related to the development of pesticide risk assessments that EPA and the Services must conduct in 

connection with their obligations under the ESA and FIFRA. 

The joint Interim Approaches were released prior to a stakeholder workshop held on November 15, 

2013. In addition, the EPA presented the joint Interim Approaches at the December 2013 Pesticide 

Program Dialogue Committee (PPDC) and State-FIFRA Issues Research and Evaluation Group 

(SFIREG) meetings. The agencies also held a stakeholder workshop in April and October 2014, 

allowing additional opportunities for stakeholders to comment on the Interim Approaches. 

Additional workshops are planned to enhance stakeholder involvement. As part of a phased, 

iterative process for developing the Interim Approaches, the agencies will also consider public 

comments on the Interim Approaches in connection with the development of upcoming 

Registration Review decisions. The details of the joint Interim Approaches are contained in the 

white paper “Interim Approaches for National-Level Pesticide Endangered Species Act Assessments 
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Based on the Recommendations of the National Academy of Sciences April 2013 Report,” dated 

November 1, 2013. 

Given that the agencies are continuing to develop and work toward implementation of the Interim 

Approaches to assess the potential risks of pesticides to listed species and their designated critical 

habitat, the ecological problem formulation supporting this Final Work Plan for dikegulac sodium 

does not describe the specific ESA analysis, including effects determinations for specific listed 

species or designated critical habitat, to be conducted during registration review. In the ecological 

problem formulation document for dikegulac sodium , EPA described the screening-level risk 

assessment to determine the potential effects of dikegulac sodium on all taxa of non-target wildlife 

and plants, which will assume that listed species and their designated critical habitats may be present 

in the vicinity of the application of dikegulac sodium . This screening-level assessment will allow 

EPA to focus its future evaluations on the types of species where the potential for effects exists 

once the scientific methods being developed by the agencies have been fully vetted. While the 

agencies continue to develop a common method for ESA analysis, the planned screening-level risk 

assessment for the registration review of dikegulac sodium will describe the level of ESA analysis 

completed for this particular registration review case. Once the agencies have fully developed and 

implemented the scientific methods necessary to complete risk assessments for endangered and 

threatened (listed) species and their designated critical habitats, these methods will be applied to 

subsequent analyses for dikegulac sodium as part of completing this registration review.
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PLANNED DATA NEEDS

Table 1 below summarizes the planned data needs for dikegulac sodium based on the EFED 

Registration Review Problem Formulation for Dikegulac-sodium and Dikegulac Sodium Human Health Scoping 

Document and Preliminary Risk Assessment. The planned data needs have not changed from what was 

included in the PWP.

Table 1: Planned Data Needs for the Dikegulac Sodium Registration Review

Guideline 

Number2 Study Title1Test Material

Estimated 

Timeframe

(Months from 

receipt of 

DCI)

Anticipated Data Needs for the Parent Dikegulac Sodium

Non-guideline Honey bee acute oral toxicity TGAI 12

Non-guideline Honey bee acute larval toxicity TGAI 12

Non-guideline Honey bee chronic larval toxicity TGAI 12

Non-guideline Honey bee adult chronic 10-day toxicity TGAI 12

RISK ASSESSMENTS FOR REGISTRATION REVIEW

The most recent comprehensive human health and ecological risk assessments for dikegulac sodium 

were completed in 2006 in preparation for the Reregistration Eligibility Decision. Findings and 

conclusions from these risk assessments are summarized in the Dikegulac Sodium: Human Health 

Scoping Document and Preliminary Risk Assessment and the EFED Registration Review Problem Formulation 

for Dikegulac-sodium.

During registration review, the Agency anticipates the need for additional data to allow for a more 

comprehensive evaluation of potential effects to honey bees. For human health, no new data are 

expected to be required to support the registration review of this pesticide. There are no hazards 

associated with dikegulac sodium at doses relevant to humans; therefore, a qualitative approach to 

risk assessment is appropriate. The Dikegulac Sodium Human Health Scoping Document and Preliminary 

Risk Assessment is expected to serve as the preliminary risk assessment for the purpose of registration 

review. EPA believes that there are no human health risks of concern associated with the currently 

registered uses of dikegulac sodium. 

Table 4 below summarizes the anticipated registration review risk assessments based on the EFED 

Problem Formulation and HED Scoping Document.

 

2 On June 27, 2012, EPA announced certain revisions in harmonized guideline series 850 – Ecological Effects Tests –

including renumbering and other designations or changes for some guideline studies. See “Final Test Guidelines; 

OCSPP 850 Series; Notice of Availability” 77 FR 38282, June 27, 2012. 

http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0154-0028
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Table 4: Planned Risk Assessments for the Dikegulac Sodium Registration Review

Type of Risk Assessment Conduct? Notes

Ecological and Environmental Fate

Comprehensive ecological 

(species to be assessed include 

terrestrial and aquatic 

organisms) 

No Ecological risk conclusions in the RED are unchanged 

and will not be reassessed. The RED determined that all 

potential risks to aquatic organisms and plants were 

below the Agency’s level of concern (LOC). All 

potential risks to terrestrial organisms were also below 

the Agency’s LOC, except for semi-aquatic non-listed 

and listed plants. However, a more comprehensive 

evaluation of potential effects to honey bees is 

anticipated. Risks to federally listed species will be 

reevaluated. 

Incidents Will check for 

updates

As of July 2014, there were no ecological incidents 

reported in EIIS or AIMS for dikegulac-sodium. There 

were also no minor incidents reported in aggregate 

incident reports.

Human Health

Dietary

Food No Dikegulac sodium does not have any agricultural or 

food production uses, as such it is designated and 

classified as a “non-food” use chemical. Based on the 

low hazard concern from the available studies, no 

endpoints of toxicological concern have been identified. 

Due to the hazard profile drinking water assessments 

are not needed. In addition, because dikegulac sodium 

is not used on any agricultural food and/or feed 

commodities and is classified as a “non-food” use 

chemical and metabolized to non-toxic substances; a 

dietary risk assessment is not required.

Drinking water No

Occupational

Handlers (mixers, loaders, 

applicators)

No While there are uses that could result in occupational 

handler and post-application exposure, due to the (very) 

low systemic toxicity of dikegulac sodium, a quantitative 

occupational risk assessment is not warranted for any 

type, or duration of exposure.

Post-application No

Residential

Handlers No Dikegulac sodium is used in small quantities by the 

professional landscaping industry, and is not marketed 

to homeowners. Residential post application exposure 

is possible from occupational application to residential 

use sites however, due to the (very) low systemic 

toxicity of dikegulac sodium, a residential quantitative 

risk assessment is not warranted for any type, or 

duration of exposure.

Post-application No

Other
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Aggregate No Evaluates the combined risk from dietary and 

residential exposures.

Cumulative No Unlike other pesticides for which EPA has followed a 

cumulative risk approach based on a common 

mechanism of toxicity, EPA has not made a common 

mechanism of toxicity finding with dikegulac sodium.

Dikegulac sodium does not appear to produce a toxic 

metabolite produced by other substances.

Tolerances No There are no tolerances to be assessed for dikegulac 

sodium.

Incidents Will check for 

updates

As of September 2014, there are no incident cases 

reported for dikegulac sodium in either the Main or 

Aggregate Incident Data System (IDS) module, Poison 

Control Centers (PCCs), California Department of 

Pesticide Regulation, National Pesticide Information 

Center (NPIC) and National Institute of Occupational 

Safety and Health’s Sentinel Event Notification System 

for Occupational Risks.

TIMELINE

EPA has created the following estimated timeline for the completion of the dikegulac sodium

registration review in Table 3 below. The projected timeline has not changed since the PWP. 

Table 5: Projected dikegulac sodium Registration Review Timeline

Activities Estimated Date

Opening the Docket

Open Docket and 60-day Public Comment Period December 2014

Close Public Comment February 2015

Case Development

Final Work Plan June 2015

Issue DCI July-September 2015

Data Submission July-September 2016

60-day Public Comment Period for Draft Risk 

Assessments3

January-March 2017

Registration Review Decision

60-day Public Comment Period for Proposed 

Registration Review Decision

June-September 2017

Registration Review Decision and Begin Post-Decision 

Follow-up

January-March 2018

Total (years) 4 years

 

3 The regulations governing Registration Review generally require the Agency to provide a public comment period of at 

least 30 calendar days for draft risk assessments; see 40 CFR Part 155.53(c). For conventional pesticides, the Agency 

plans to provide a 60 calendar day public comment period generally for draft risk assessments.
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NEXT STEPS

As noted previously, the Agency plans to require several ecological effects studies for dikegulac 

sodium through a Data Call-In Notice, expected to be issued in late 2015.