Clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) is a selective herbicide used for control of broadleaf weeds, especially thistles and clovers.
Clopyralid is in the pyridine family of herbicides, which also includes picloram, triclopyr, and several less common herbicides. For control of Creeping Thistle, Cirsium arvense, a noxious, perennial weed, clopyralid is one of the few effective herbicides available. It is particularly active on members of the Asteraceae and the Fabaceae. It does not affect members of the Poaceae (grasses).
Clopyralid is notorious for its ability to persist in dead plants and compost, and has accumulated to phytotoxic levels in finished compost in a few highly publicized cases. In Seattle, Washington, clopyralid was widely used for weed control in lawns until prohibited in 1999. There, a city-mandated curbside grass clipping collection and composting program produced compost with measurable levels of clopyralid. Subsequently, DowAgro, the manufacturer of clopyralid, voluntarily deregistered it for lawn uses.
Clopyralid is licensed for lawn use in France and under the following names: Bayer Jardin: Désherbant jeune gazon and Scanner Sélectif gazon Vilmorin: désherbant Gazon LONPAR. Brand names of clopyralid in the US market include Stinger, Transline, Reclaim.