Spent spearmint hay from mint that had been treated with clopyralid in the fall or spring injured ‘Russet Burbank’ potato planted into loamy sand soil amended with 50 g hay/kg soil. Lowering the ratio of mint hay to soil from 50 to 3.1 g/kg reduced, but did not eliminate, the injury to potato. Potato was inured by clopyralid at concentrations as low as 3 ppbw in soil.