Oxadiazon Update

One issue on the minds of many turfgrass managers last year was the Environmental Protection Agency (EPA) registration review for oxadiazon and the proposed interim decision released in August 2021. Oxadiazon is a key active ingredient in several herbicides used for annual weed control in warm- and cool-season turfgrass (e.g., Ronstar®, The Andersons Goose/Crab Control, etc). The interim use patterns proposed would have limited turfgrass managers’ ability to effectively use this active ingredient as part of weed control programs. Golf course applications would have been restricted to fairways only (i.e., no further use on greens, tees, or roughs) and applications to sports fields would have been completely prohibited.

Goosegrass (Eleusine indica) emergence

As is standard practice with EPA proposed decisions on active ingredients, a public comment period ensued throughout autumn 2021. Nineteen turfgrass weed scientists at land-grant universities submitted a joint letter to the EPA communicating the importance of oxadiazon for controlling problematic weeds on golf courses and sports fields, particularly in light of increased herbicide-resistance issues in recent years. The Golf Course Superintendents Association of America, Sports Turf Managers Association, and Turfgrass Producers International all submitted letters communicating the importance of oxadiazon in turfgrass, along with several industry partners with oxadiazon-based herbicides in their portfolio (e.g., Bayer, ADAMA, The Andersons, etc).

This collaboration was well received by EPA and in late March 2022, the final re-registration decision on oxadiazon was announced. The full document can be accessed online.

What’s the Final Decision?

Below is a breakdown of the label changes affecting oxadiazon use for weed control in turfgrass.

1. Herbicides containing oxadiazon will become restricted use products limited for use by certified applicators. This was a good-faith compromise on the part of EPA and the turfgrass industry to facilitate the continued use of oxadiazon for weed management.
2. All existing oxadiazon use sites will be maintained. Oxadiazon will continue to be available for weed management on golf courses, sports fields, and parks, as well as sod production.
3. The single application use rate will now be capped at 3 lb ai/A. Golf courses and sports fields can only use liquid formulations of oxadiazon once annually, prior to granular treatment. Additional applications of oxadiazon (after 3 lb ai/A has already been applied) must be delivered via a granular product. In a calendar year, the total application rate of oxadiazon (from liquid + granular formulations) must not exceed 6 lb ai/A. In situations of heavy weed pressure, golf courses can elect to make two applications of granular product at 4 lb ai/A in a calendar year.
4. The interval between applications in turfgrass must be 60 days or more
5. Use of oxadiazon on all golf course playing surfaces (i.e., fairways, roughs, greens, tees, etc) will remain. However, ≤ 30% of the total managed turfgrass area can be treated yearly.
6. Golf courses and sod farms must include a ≥ 10 ft vegetative buffer when treating areas adjacent to surface water