An aqueous microbicidal composition having two components. The first component is a nonionic surfactant with structure: R1O(CH2CH(CH3)O)5(CH2CH2O)9H, where R1 is a C8 alkyl group. The second component is phenoxyethanol. The weight ratio of the nonionic surfactant to phenoxyethanol is from 1:1 to 1:18.2766.