The present invention relates to a composition comprising dimethomorph and fosetyl-aluminium. The composition is claimed to be used in a method of reducing the E/Z isomerization of dimethomorph, a method of reducing the instability of the fungicidal activity of dimethomorph in the presence of light and a method of preventing or reducing fungal infestations of plants at a locus. The fosetyl-aluminium is thought to act as a conversion agent reducing the conversion of the Z isomer of dimethomorph to the E isomer upon exposure to light.
