AbstractSeventy analogues of chloraniformethan and triforine were prepared and tested for activity against barley powdery mildew caused byErysiphe graminis.Structural variations, including replacement of the trichloromethyl, formamido, 3,4‐dichloroanilino or piperazin‐1,4‐diyl groups, yielded information concerning the structural characteristics required for activity in leaf‐spray or root‐drench tests, and it appears that the XCHNHCO grouping (where X=substituted nitrogen, oxygen or sulphur) is a prerequisite for