The Influence of Clopyralid in Soil on Crop Growth and Morphology of Aboveground Parts

Abstract

In recent years, physiological disorders of crops caused by compost with residual clopyralid, a growth regulator herbicide registered for use in feed-exporting countries, has become a problem in Japanese agriculture. Thus, we compared the influence of clopyralid on the dry weight and morphology of aboveground parts in major crops of 23 plant species in 13 families according to the soil concentrations. We considered the characteristic symptoms by focusing on leaf shape. No effect of clopyralid on growth was observed in Welsh onion, oat, barley, spinach mustard, buckwheat, spinach, or sesame. However, clopyralid resulted in physiological growth disorders such as decreasing dry weight and/or abnormal morphology of aboveground parts in 16 plant species in seven families, including Fabaceae, Solanaceae, and Asteraceae. In particular, rugose leaves were observed in 13 plant species belonging to Fabaceae, Solanaceae, Campanulaceae, Asteraceae, and Apiaceae regardless of the leaf shape. These crops exhibited rolling up of the leaf margin, cupping, and curling up of the serrations before any apparent rugose leaves, and these are considered to be the initial physiological disorders of rugose leaves. These initial physiological disorders may depend on the shape of the leaf margin, such as having or not having serrations or lobes, rather than the shape of the leaf blade. Therefore, we suggest that observing the shape of the leaf margin could be used to determine any effect of clopyralid on crops belonging to families with high sensitivity to clopyralid, such as Fabaceae, Solanaceae, and Asteraceae.