PYIDOZINONE DERIVATIVES AND THEIR USE AS AGRICULTURAL FUNGICIDES

Certain 6-(substituted phenyl)-3(2H)-pyridazinones and 6-(substituted phenyl)-4,5-dihydro-3(2H)-pyridazinones, in which the substituted phenyl group has a halogen atom at one or both of the 3- and 5- positions, are useful as agricultural fungicides. The compounds have the formula I. ¢in which: R1 represents a hydrogen atom, a hydroxy group, a group of formula -O-CO-R5 (in which R5 represents an alkyl group having from 1 to 5 carbon atoms) or a group of formula -O-SO2-R6 (in which R6 represents a phenyl group which is unsubstituted or has one or more halogen or C1-3 alkyl substituents); R2 and R4 are the same or different and each represents a halogen atom, or one of R2 and R4 represents a halogen atom and the other represents a hydrogen atom; R3 represents a hydrogen atom, an alkyl group having from 1 to 6 carbon atoms, an alkoxy group having from 1 to 6 carbon atoms, an alkenyloxy group having from 3 to 5 carbon atoms, an alkynyloxy group having 3 or 4 carbon atoms, an amino group, a hydroxy group, a halogen atom, a group of formula -O-CO-R5 (in which R5 is as defined above) or a group of formula -O-SO2-R6 (in which R6 is as defined above); and A represents the group -CH2-CH2- or - CH=CH-! or, when A represents the group -CH=CH-, a salt thereof.