This invention relates to derivatives of acrylic acid useful in agriculture (especially as fungicides but also as plant growth regulators, insecticides and nematocides), to processes for preparing them, to agricultural (especially fungicidal) compositions containing them, and to methods of using them to combat fungi, especially fungal infections in plants, to regulate plant growth and to kill or control insect or nematode pests. The invention provides a compound having the formula (I): STR1 and stereoisomers thereof, wherein W is a substituted pyridinyl or substituted pyrimidinyl group linked to A by any of its ring carbon atoms; A is either an oxygen atom or S(O)n wherein n is 0, 1 or 2; X, Y and Z, which are the same or different, are hydrogen or halogen atoms, or hydroxy, optionally substituted alkyl (including haloalkyl), optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted alkoxy, (including haloalkoxy), optionally substituted alkylthio, optionally substituted aryloxy, optionally substituted arylalkoxy, optionally substituted acyloxy, optionally substituted amino, optionally substituted acylamino, nitro, cyano, --CO2 R3, --CONR4 R5, --COR6 or --S(O)m R7 (wherein m is 0, 1 or 2) groups, or any two of the groups X, Y and Z, when they are in adjacent positions on the phenyl ring, may join to form a fused ring, either aromatic or aliphatic, optionally containing one or more heteroatoms; R1 and R2, which are the same or different, are optionally substituted alkyl (including fluoroalkyl) groups provided that when W is 5-trifluoromethylpyridin-2-yl, A is oxygen, X is hydrogen, and R1 and R2 are both methyl, Y and Z are not both hydrogen, Y is not F, Cl, methyl, nitro, 5--CF3, 5--SCH3 or 4--(CH3)2 N if Z is hydrogen and Y and Z together are not 3-nitro-5-chloro, 3,5-dinitro, 4,5-dimethoxy or 4,5-methylenedioxy; and R3, R4, R5, R6 and R7, which are the same or different, are hydrogen atoms or optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted cycloalkylalkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted aryl or optionally substituted aralkyl groups; and metal complexes thereof.