EPA issues proposed interim decision on registration review for sulfonylurea herbicides

The Environmental Protection Agency registration review is a process that every registered pesticide undergoes at least every 15 years to ensure that it continues to meet the Federal Insecticide, Fungicide, and Rodenticide Act standard for registration. In July 2016, EPA issued its proposed interim decision (PID) on the registration review for 22 sulfonylurea (SU) herbicides. Two herbicides used in forestry, sulfometuron methyl (SM) and metsulfuron methyl (MM), were among those 22 SU herbicides.

In the interim decision, EPA concluded that there are no human health risks of concern related to continued use of SU herbicides. The agency also determined that there are no direct ecological risks for any taxa other than non-target terrestrial and aquatic plants.

To reduce potential risk to non-target plants from spray drift, EPA proposed a number of changes to the product labeling for SU herbicides. The approach taken represents a significant departure from the agency’s prior practice, which has been to rely primarily on increasing no-spray buffer width to reduce potential off-site impacts.

Instead, EPA proposed no mandatory no-spray buffers, but rather chose to require the use of a number of other spray drift reduction technologies, including an emphasis on using “the coarsest spray droplet size spectrum that would still be efficacious for target weed control.” It appears that this represents a fundamental change in EPA’s approach to pesticide risk mitigation, because other PIDs released at the same time (e.g., the insecticide tebufenozide) contain the same proposed label language.

Specific measures for aerial applications proposed for SU herbicides in the PID include the following.

(1) When applying aerially to crops, do not release spray at a height greater than 10 ft. above the crop canopy, unless a greater application height is necessary for pilot safety.

(2) Applicators are required to use an Extremely Coarse droplet size (ASABE S572.1).

(3) When applying to crops via aerial application equipment, the spray boom must be mounted on the aircraft so as to minimize drift caused by wing tip or rotor blade vortices. The boom length must not exceed 75% of the wingspan or 90% of the rotor blade diameter.

(4) When applying to crops via aerial application equipment, applicators must use ½ swath displacement upwind at the downwind edge of the field.

(5) Nozzles must be oriented so the spray is directed toward the back of the aircraft.

(6) Do not apply when wind speeds exceed 10 miles per hour at the application site.

(7) Do not apply during temperature inversions.

In addition, EPA noted in the PID that some current SU product labels do specify mandatory buffer restrictions. The agency stated that it does not intend to remove or modify any of those restrictions as a default action, but indicated that it is open to reviewing any existing mitigationmeasures (e.g., buffer requirements) on a case-by-case basis. The current SM label requires 75 ft. no-spray buffers for aerial applications and 50 ft. buffers for ground applications.

NCASI staff have submitted comments to EPA pointing out that there is no scientific basis for continuing to require these buffers for SM.

The SU PID is available online at https://www.regulations.gov/document?D=EPA-HQ-OPP-2015-0625-0030. For additional information on the PID or the comments submitted to EPA by NCASI, please contact Dr. Vickie L. Tatum.


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