The invention relates to a fungicidally active compound of the general Formula (I): where Het is a 5- or 6-membered heterocyclic ring containing one to three heteroatoms, each independently selected from oxygen, nitrogen and sulphur, the ring being substituted by the groups R3, R4 and R5; R1 and R2 are independently H, halo, C1-4 alkyl or C1-4 haloalkyl; and R3, R4 and R5 are each, independently, H, halo, C1-4 alkyl, C1-4 haloalkyl or C1-4 haloalkoxy, provided that at least one of R3, R4 and R5 is not H; to the preparation of these compounds, to novel intermediates used in their preparation, to agrochemical compositions which comprise at least one of the novel compounds as an active ingredient, to the preparation of the compositions and to the use of the active ingredients or compositions in agriculture or horticulture for controlling or preventing infestations of plants by phytopathogenic microorganisms, especially fungi.