Update on Atrazine and Simazine Use in Turfgrass Systems

— Written By

Travis Gannon and Tripp Rogers

Background

Atrazine and simazine are triazine herbicides registered for pre- and post-emergent control of many broadleaf and grassy weeds. The efficacy and cost associated with these herbicides make them a common choice among warm-season turfgrass managers. Currently, they are registered for use on golf courses, athletic fields, residential/commercial lawns, sod farms as well as agronomic crops such as corn, sugarcane, conifers, orchard, vineyard, and berry crops.

What Happened?

The Food Quality Protection Act of 1996 dictates that at least once every 15 years, registered pesticides must undergo review. This review, undertaken by the US EPA determines whether a pesticide continues to meet standards for registration. In January 2020, US EPA announced the proposed interim decision for simazine and atrazine and took public comments for 60 days. In September 2020, the agency released the interim decision for simazine and atrazine and the full summaries are accessible at: Atrazine and Simazine.

Changes for Atrazine:

Atrazine registrants voluntarily modified the label to include:

  • Remove roadside use sites from labels.
  • Remove conifer uses including Christmas trees, timber, and all forestry uses.
  • Require an infield downwind buffer of 15 feet for ground applications and 150 feet for aerial application form the edge of streams and rivers and from threatened endangered species habitats.
  • Applicators are required to use nozzles that produce medium or coarser droplet size.

Residential Turf Mitigation

  • Granular formulations: Single maximum application rate on residential turf reduced from 2.2 lb ai per acre to 2.0 lb ai per acre.
  • Sprayable formulations: Single maximum application rate on residential turf reduced from 2.0 lb ai per acre to 1.0 lb ai per acre.
  • Restrict applications in “landscape turf” to spot treatments.

Athletic Fields

  • The interim decision does not explicitly state any changes pertaining to athletic fields.

Golf Courses

  • The interim decision does not explicitly state any changes pertaining to golf courses.

Changes for Simazine:

Simazine registrants voluntarily modified the label to include:

  • Restrict to warm-season turfgrass only.
  • Remove “shelterbelt” use (i.e, a line of trees/shrubs planted to protect an area from strong winds or other factors contributing to erosion).
  • Restrict forestry uses to Christmas trees only.
  • Require an in field downwind buffer of 15 feet for ground applications and 150 feet for aerial application form the edge of streams and rivers and from threatened endangered species habitats.
  • Applicators are required to use nozzles that produce medium or coarser droplet size.
  • Do not apply when wind speeds exceed 10 MPH.
  • Do not apply during temperature inversions.

Residential Turf Mitigation:

  • Reduce single maximum application rate from 2 lb ai per acre to 1.6 lb ai per acre with 0.5 in of irrigation immediately following application to turf.
  • Reduce single maximum rate to 0.65 lb ai per acre without irrigation.

Athletic Fields

  • The interim decision states all labels with recreational turf use including sports fields, parks, and recreational areas need to include one or both label restrictions:
    • Reduce single maximum application rate from 2 lb ai per acre to 1.6 lb ai per acre with 0.5 in of irrigation immediately following application to turf.
    • Reduce single maximum rate to 0.65 lb ai per acre without irrigation.

Golf courses and sod production fields:

  • No label changes required.

Implications for turfgrass managers:

The irrigation requirement immediately after application in residential turf may severely limit the utility of simazine for lawn care operators. Due to the absence of irrigation systems in many residential lawn settings as well as the inability of lawn care operators to control irrigation, the reduced single maximum rate of 0.65 lb ai per acre will limit the efficacy of this product. It is likely there will be a need for alternative herbicides to achieve comparable control. While alternative products are available, in many cases, they are significantly more expensive.

NOTE: It’s important to note changes discussed in this article pertain to use patterns and implications; however, additional label changes to mitigate human and environmental health risks were developed and can be found in the full summary.

Travis Gannon is an Associate Professor in the Department of Crop and Soil Sciences at NC State University (twgannon@ncsu.edu)

Tripp Rogers is a PhD student in the Department of Crop and Soil Sciences at NC State University (rrroger3@ncsu.edu)