A composition comprises a substantially dry mixture of substantially dry corn gluten meal and substantially dry solid acid, wherein the amount of the substantially dry solid acid is effective to enhance the pre-emergence herbicidal activity of the substantially dry corn gluten meal. A method for selectively inhibiting the growth of undesirable plants comprises prior to the emergence of the undesirable plants, applying a substantially dry corn gluten meal and a substantially dry solid acid to a plot of soil so that the amount of the substantially dry solid acid applied to the plot of soil is effective to enhance the pre-emergence herbicidal activity of the substantially dry corn gluten meal, wherein the substantially dry corn gluten meal and the substantially dry solid acid are applied in an amount effective to inhibit the growth of the undesirable plants.
