A method of treating a grass-carrying surface, the method comprising applying to the g carrying surface: (a) a compound of formula (I): or a derivative salt thereof wherein L is a linking group; each of R1, R2 and R3 is independently selected from an optionally substituted alkyl, alkenyl, aryl or alkoxy group; R4 is oxygen or an optionally substituted alkyl, alkenyl or aryl group; each of R5 and R6 is an optionally substituted alkyl, alkenyl or aryl group; and n is 0 or 1; (b) at least one cationic biocide; (c) a hydrocarbyl saccharide compound; and (d) a nonionic surfactant.