1/21/16 Thidiazuron Risk Mitigation Teleconference: Meeting Notes

EPA attendance: Khue Nguyen (PRD), Christina Motilall (PRD), Melissa Grable (PRD), Mark Corbin

(EFED), Stephen Carey (EFED), Bill Eckel (EFED), Kathryn Montague (RD), Steve Smearman (BEAD), Sunil 

Ratnayake (BEAD), Monisha Kaul (BEAD)

Industry attendance (via teleconference): Danielle Larochelle (Nufarm), Jamin Huang (Bayer), Trish 

Sheehy (Adama), Rodney Akers (Arysta), Chris Mason (Loveland), Eric Henry (Bayer), Brad Glenn (Bayer), 

Alex Nikolakis (Bayer)

Notes:

EPA was supportive of thidiazuron’s continued registration as it was a chemical with low risks and high 

benefits. EPA was primarily interested in addressing spray drift risk to certain sensitive dicots (ex. 

lettuce). EPA proposed via email correspondence (dated 1/13/16) the following proposed risk 

mitigation measures for the thidiazuron labels, with the goal of achieving greater protection from spray 

drift and more parity between all the different labels:

1. No aerial application within 0.5 miles of lettuce (this language already appears on some labels)

2. No aerial application within 5 miles upwind of citrus in flush (this language already appears on 

some labels)

3. No ground application within 100 feet of lettuce (this language already appears on some labels)

4. No ground application within 0.5 miles upwind from citrus (this language already appears on 

some labels)

5. Apply with medium or coarser spray (according to ASAE standard 572) for standard nozzles for 

both aerial and ground applications (this language already appears on some labels)

6. When using ground application, apply with nozzle height no more than 2 feet above the ground 

or crop canopy (this language already appears on some labels)

7. Mixtures with organophosphates can increase non-target crop phytotoxicity. Additional care 

should be exercised when lettuce, citrus, cantaloupes or any other edible crops are adjacent to 

treated cotton fields (this language already appears on some labels).

8. Maximum application rate of 0.3 pounds of active ingredient per acre per year (this was RED risk 

mitigation, this language already appears on most labels, all registrants need to check that this 

appears on their label).

9. Maximum of 2 applications, but not to exceed 0.3 pounds of active ingredient per acre per year 

(this language already appears on some labels)

10. Minimum retreatment interval of 21 days (this language already appears on some labels)

Industry unanimously agreed to implement measures 1-9, but had comments on item number 10. 

Nufarm was concerned about the 21-day minimum retreatment interval (MRI) restriction and thought it 

was unjustified for several reasons:

1) the 21 day MRI requirement that appears on some thidiazuron labels was for products coformulated with diuron and was meant to satisfy the diuron RED requirements 

2) the thidiazuron RED did not specify a requirement for a 21-day MRI
3) the 21-day MRI restriction interferes with situations where two successive applications of 

thidiazuron are needed to ensure adequate defoliation. Often a second application of defoliant 

is applied approximately 7 days after the first application.

4) The 21-day MRI restriction is not supported by current dissipation data for thidiazuron

There was some discussion about the single application rate of thidiazuron, the maximum application 

rate of thidiazuron, and the thidiazuron application rates on thidiazuron/diuron labels and how it related 

to the 21-day MRI restriction, but it was difficult to understand over the phone. 

EPA suggested that Nufarm submit comments via email so EPA could fully review. Nufarm agreed to 

submit comments separately via email. EPA stated it would follow up regarding item 10 once it had a 

chance to review comments.

EPA discussed next steps for thidiazuron. EPA intended to publish the proposed interim decision for 

public comment in March 2016. EPA intended to require the full suite of pollinator data for thidiazuron 

in a GDCI to be issued in the near future, noting that industry would not have to initiate tier 2 and tier 3 

pollinator testing until EPA had completed tier 1 pollinator screening and given notice that tier 2 and tier 

3 data were required. 

Industry thought that additional pollinator data were unjustified since current data indicates that 

thidiazuron is not very toxic to bees. EPA said that requiring additional pollinator data was consistent 

with its new policy for pollinator risk assessment. Thidiazuron was among a list of many chemicals with 

additional pollinator data requirements. In addition, exposure to pollinators could not be precluded 

because cotton flowering was intermittent and some flower buds may still be open during thidiazuron 

application. 

The meeting was subsequently disbanded.