a method of controlling take - all disease of plants by applying , preferably to the seed prior to planting , a fungicide of the formula ## str1 ## wherein z 1 and z 2 are c and are part of an aromatic ring that is thiophene ; a is selected from -- c - amine , -- c -- sr 3 , -- nh -- cr 4 , and -- c -- xr 7 ; b is -- w m -- q 3 or selected from o - tolyl , 1 - naphthyl , 2 - naphthyl , and 9 - phenanthryl , each optionally substituted with halogen or r 4 ; q is c , si , ge , or sn ; w is -- c p h . sub . --; or when q is c , w is selected from -- c p h . sub . --, -- n m h . sub . --, -- s p --, and -- o --; x is o or s ; n is 0 , 1 , 2 , or 3 ; m is 0 or 1 ; p is 0 , 1 , or 2 ; r , r 2 , r 3 , r 4 and r 7 are herein defined ; or an agronomic salt thereof .