Evaluation of the influence of residual herbicide clopyralid in compost on the growth of several ornamental plants

Abstract

Growth disorders of horticultural crops caused by clopyralid residues in manure compost derived from imported livestock feeds have been reported. In this study, symptoms of clopyralid injury in several ornamental plants were observed, and the degree of their susceptibility was evaluated by using test media containing 0 – 25 µg·kg ^-1 -DW of clopyralid. Clopyralid-induced injuries were observed in members of the Asteraceae family, such as chrysanthemum (Chrysanthemum × morifolium), marigold (Tagetes patula), cosmos (Cosmos bipinnatus), aster (Callistephus chinensis), sunflower (Helianthus annuus), and zinnia (Zinnia elegans), and Fabaceae family (crimson clover [Trifolium incarnatum]). Symptoms were observed within 2 weeks of sowing or planting on the test media. The common symptoms were inward rolling of the margins of new developing apical leaves, cessation of or abnormally shaped stem apex and flower buds, and reduction in stem length and fresh weight of the above-ground parts. In sunflower, an abnormal hypocotyl elongation was observed. The degree of these symptoms was dependent on clopyralid concentration. No clopyralid induced injuries were observed in plants belonging to the Violaceae (Pansy [Viola × wittrockiana]) and Gentianaceae (eustoma [Eustoma grandiflorum]).