. "Preferably the 2,3-dihydro-1,4-phthalazinedione is of the formula ##STR7## wherein R1 is an amino and each of R2, R3 and R4 is optionally substituted C1 -C6 -alkyl or alkenyl, hydroxyl, C1 -C6 -alkoxy, carboxyl or amino or R2 is amino and each of R1, R3 and R4 is H, unsubstituted or substituted C1 -C6 -alkyl or alkenyl, hydroxyl, C1 -C6 -alkoxy, carboxyl, or amino or R1 and R2 are together in a ri" . . .