Abstract: A method of controlling the population of a first microorganism at a foliar locus by preferentially enhancing the population of a second microorganism at said locus, comprises applying to the locus an amount of a durable selective habitat enhancer which substantially preferentially potentiates growth of said second microorganism with respect to said first microorganism. The durable selective habitat enhancer preferably comprises a substantially water-insoluble, weather resistant polymeric substrate and a binder which increases the durability of the habitat enhancer. The second microorganism can be endogenous to the foliar locus or exogenously applied. Chitin and cellulose are preferred habitat enhancers.