Methods for controlling the growth of microorganisms in or on a product, material, or medium, such as a fermentable or fermenting medium, susceptible to attack by a microorganism, by treating with aqueous solution comprising monochloramine and at least one organic acid in a synergistically microbicidally effective combined amount to control unwanted microbial growth. Microbicidal aqueous solutions containing monochloramine and at least one organic acid in a synergistically microbicidally effective combined amount to control the growth of at least one microorganism are also described.
