Compounds of the general formula I or II
 wherein A represents an optionally substituted alkyl, alkenyl, cycloalkyl, cycloalkenyl, dialkylamino, aryl, heteroaryl, aralkyl or heteroaralkyl group; R1 represents a hydrogen atom or an acyl group; and R2 represents an optionally substituted alkyl, alkenyl, aryl, heteroaryl, aralkyl or heteroaralkyl group are useful as herbicides. They are new per se except for the N-benzylamide of 5-(2-furyl)-1,2,4-thiadiazole-3-carboxylic acid.
                            通式 I 或 II 的化合物
 其中 A 代表任选取代的烷基、烯基、环烷基、环烯基、二烷基
氨基、芳基、杂芳基、芳烷基或杂烷基;R1 代表氢原子或酰基;R2 代表任选取代的烷基、烯基、芳基、杂芳基、芳烷基或杂烷基。除了 5-(2-呋喃基)-
1,2,4-噻二唑-3-
羧酸的 N-苄基酰胺外,它们本身就是新产品。