The influence of formulation, exposure time, and pH on the herbicidal action of dalapon foliar sprays tested on corn

Technical and commercial dalapon were tested on corn, with or without one of the surfactants: Vatsol OT, Dynawet, and X-77. Acid dalapon and four of its salts also were tested. The acid and the sodium salt were about equal in effectiveness. The advantage of using various additional surfactants was amply demonstrated. Dalapon penetrated corn leaves most readily in the nondissociated form, or at low pH in aqueous solutions. However, acute toxicity at very low pH interfered with translocation, which is necessary for effective growth inhibition by the herbicide. Optimum herbicidal results were obtained at about pH 6, near the pH of a solution of commercial dalapon in tap water. The toxicity to corn of various dalapon formulations is discussed and interpreted in relation to known physicochemical properties of the parent compound, 2,2-dichloropropionic acid.