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Cyhalofop-butyl FOCUS meeting, July 11, 2014

Michelle Ranville- author

Attendees: Jolene Trujillo, Jill Bloom (PRD); Michelle Ranville, Bill Phillips, Rafael Prieto (BEAD); 

Jean Holmes, Richard Shamblen (EFED); Doug Dotson, Margarita Collantes (HED); Nneka Breaux, 

Rafael Herrera, Rick Mann, Glenda Gordon (Dow AgroScience)

Meeting Notes: 

DAS presented a powerpoint that contained answers to many of EPA’s questions about cyhalofopbutyl usage in rice. Those responses + additional comments are contained in these notes, but there 

was some other background in the powerpoint that is not in these notes. That PPT is saved as 

“DAS_EPA_FOCUS Meeting.pptx” at G:\~Registration Review\Chemicals\Cyhalofop-butyl 

EPA Question: Where is cyhalofop-butyl used in dry- and wet-seeded rice in the U.S.?

DAS Response: Cyhalofop-butyl is used in Arkansas, California, Louisiana, Mississippi, Missouri, and 

Texas.

- CA is 99% water-seeded

- LA and AK also have water-seeded rice but much lower levels

- MS, MO, and TX have minimal or zero water-seeded rice. 

EPA Question: Discuss the spectrum of plants that are affected by the mechanism of action for this 

chemical.

DAS Response: Cyhalofop-butyl only affects grasses. It has no activity against broadleaves or sedges.

- There is a buffer for peaches of 2-4 miles because they are allergic to the AI. DAS did tests to 

find out the appropriate buffers. This is only a concern in CA because peaches are not grown 

in the other rice-growing regions

- It is necessary to add an adjuvant to cyhalofop-butyl or it would not have efficacy against 

grasses. It needs the adjuvant to penetrate the waxy coating on weeds. Many post-emergent 

herbicides use an adjuvant for this reason

EPA Question: Discuss DowAgroSciences plan for wild rice

DAS Response: DAS does not plan to label wild rice and will remove the use from existing unstamped 

labels

EPA Question: Can Dow clarify the term “post-flood?” For example, in water-seeded rice, is the 

“post-flood” application the period after the flood for seeding, or application period after permanent 

flood?

DAS Response: Post-flood refers to any time after seeding that the fields are flooded with water and 

that grass weeds would be present in the rice. Thus, post flood can be both of the examples provided.
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EPA Question: Why can the granule formulations be only applied to “water-seeded” rice? It seems 

that the granule could be applied to “dry-seeded” rice since the granule is applied to flooded waters.

DAS Response: The Clincher granule can only be used to control grasses that are completely (>80%) 

submerged at the 1-3 leaf vegetative stage. In water seeded rice, the rice is flooded the whole time 

and grass weeds can be controlled while they are still submerged at the 1-3 leaf stage. In dry seeded 

rice, the permanent flood is only established once the rice tillers, typically 4-6 weeks after planting. 

Once you flood the field at this stage, grasses are typically tillered (advanced growth stage) and are 

NOT submerged. Thus the granule cannot be used to control the grass weeds due to their large size 

and little foliage under water for herbicide uptake. 

- If you wait for permanent flood, the weeds would be 80% out of water and granules would 

not work. The granules are broadcast over the water and dissolve killing the small weeds.

- Clincher also cannot be applied under drought stress (i.e., after pre-flood and before 

permanent flood), so liquid formula may be applied after permanent flood. 

- Normally growers don’t like to drain water, but 80% must be exposed for liquid foliar 

application to work. So if there is rain, they would have to lower the water prior to 

application.

- A “flush” just means that water is entered into one end of the field until the field is soaked. 

The water is not drained. 

- The rice field has a levy around it that is 12-18 inches high, so there is no way for water to 

drain naturally. Also, the soil is very compacted so water is not lost.

- Liquid is basically a “rescue” application, only used if weeds poke through.

EPA Question: How is clincher used in the ratoon rice production process?

DAS Response: In Louisiana, very little Clincher is used in ratoon rice. An estimated 50 gallons per 

season is applied which – at the 13 oz/acre rate – would treat less than 500 acres. It is typically used 

as a spot spray, not broadcast, to control patches of grass weeds.

- Almost all ratoon rice is grown in LA, at least as far as DAS knows because that is the only 

place they see Clincher applied to ratoon rice.

- After the first crop is harvested, the field is drained and plowed. Then flooded again and 

ratoon crop might provide small second harvest. It would not be worth much to spray with 

herbicide and it would have to be planned well to meet the 60-day PHI

- Only 20% or less of rice gets Clincher application, in general, so probably very small amount 

in ratoon rice.

EPA Question: How are buffer zones established? Buffer distances for the same commodity vary 

among labels. In particular, for endangered species, the RebelEX has a smaller distance for the 

Southern States than California.
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DAS Response: Buffer zones are established with modeling and actual drift studies. An additional 

safety margin was applied for the products used in CA because of the local conditions. 

- In products with multiple AIs, the buffer zone was based on the more toxic (Clincher)

- In CA, timing of other crops relative to rice matters, e.g., young wheat nearby in CA at time 

of Clincher application versus older wheat in LA which is not as susceptible

- Also, Rebel X (with smaller buffers) is labeled for use in CA but not marketed there.

EPA Question: There are two 24c labels for CA with higher application rate for one-time even.

DAS Response: They want to keep this use.