A fungicide which contains obtusaquinone, ##SPC1## A method of controlling marine fungi by which obtusaquinone of the above formula is applied to the material to be protected.
Substances, particularly wood, which are normally subject to deterioration due to marine borers are preserved by applying to the substance certain 4-(3-phenylpropenylidene)-2,5-cyclohexadieneones substituted at position 5 with substituents selected from the group consisting of lower alkyl, lower alkoxy, and hydrogen, and at position 2 with substituents selected from the group consisting of hydroxyl and lower alkoxyl.
