Two‐week‐old wheat (Triticum aestivum L. cv. Fredrick), peas (Pisum sativum L. cv. Little Sweetie) and soybean (Glycine max L. cv. Hodgson) seedlings were transferred to paper cups containing various concentrations of triadimefon [1‐(4‐chlorophenoxy)‐3,3 dimethyl‐1‐(1H‐1,2,4‐triazol‐1‐yl)‐2‐butanone] a fungicide. Twelve days after treatment, triadimefon (20 μg ml−1) significantly reduced transpiration in wheat, peas and soybeans by 40, 29 and 19%, respectively. The reduction of transpiration prevented the leaves from wilting and becoming senescent. In another experiment, triadimefon was applied as a soil drench after the initiation of flowers in soybeans and peas and after swelling in radish (Raphanus sativus L. cv. Cherry Belle) roots. After treatment the water level was maintained at half field capacity. In all three species, the treated plants were shorter, more compact and had thicker and greener leaves than the control plants. In the case of radish, the treatment also prevented flowering. Triadimefon significantly increased the seed yield of soybeans and peas and the root to shoot ratio in radish. Hence root application of triadimefon reduces transpiration, protects plants, and increases yield under water stress conditions.