By Steve Tomasko, UW PAT Program Outreach Specialist

The Environmental Protection Agency (EPA) will require new restrictions on the use of the herbicides aminopyralid and picloram. Aminopyralid and picloram are in the class of herbicides known as pyridines. These herbicides are registered for use in both agricultural and non-agricultural areas. Agricultural use sites include pastures and rangeland. Non-agricultural use sites include turf, industrial areas, and right-of-ways.

The active ingredient picloram is found in brand name herbicides such as Triumph, Tordon, and Trooper, among others. The active ingredient aminopyralid is found in brand name herbicides such as Milestone, Whetston, and Capstone. The problem the EPA has found with the use of these two herbicides is that they do not degrade quickly and often residues end up contaminating compost. When that compost is used on fields, residential gardens and lawns and other sites, the herbicide residues can then damage nontarget plants. Compost contamination occurs when treated materials, or manure from animals that consumed treated materials, are collected and recycled into compost.

These concerns prompted the EPA to issue an “interim registration review decision” for these two active ingredients. The interim decision is one of the final stages of the registration review process and implements risk mitigation to address risks of concern.

The EPA will now require the following mitigation measures to reduce the potential for residues of these herbicides in compost:

• Prohibition of off-site use of treated plant materials and manure from grazing animals for compost and animal bedding/feed until 18 months after application to allow for residues to decline.
• Requiring that livestock be grazed on forage that haven’t been treated for three days before moving to a site where manure is collected, or sensitive crops are grown.
• Requiring pasture applicators to notify the property owners/operators of the compost prohibition, and for the applicator to keep a record of this notification for two years.
• Updating compost pictogram on pesticide labels showing growers/operators how to manage treated materials.
• Requiring registrants (manufacturers of products containing the active ingredients) to participate in a stewardship program and provide educational outreach for applicators, growers, land managers, and others affected by herbicide residues in compost.

Additional information on the pyridine and pyrimidine herbicides and interim decisions are available on EPA’s website.