The application of livestock manure compost contaminated with the herbicide clopyralid originating from imported grass hay and grains can cause crop growth disorder.　On examining the susceptibility of ornamental crops, growth disorders were observed in chrysanthemum, cosmos, zinnia, sunflower, aster （Asteraceae）, and crimson clover （Leguminosae） plants.　Therefore, more simple assay methods for assessing clopyralid content and technology for reducing clopyralid amount in compost and soil are required.