Energen 20% Vinegar Weed & Grass Killer is a quick-acting, non-selective contact herbicide containing an organic acid for which the residues degrade promptly in the soil. Foliar contact results in rapid desiccation and control of annual weeds and grasses, and top growth reduction of herbaceous perennial weeds and grasses. For control of established perennial weeds, retreatment may be necessary. It may be applied up to two days before harvest. Active ingredient: acetic acid.