Studies with 3,5‐diiodo‐4‐hydroxybenzonitrile (ioxynil) and related compounds in soils and plants

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Abstract
SUMMARY: The inactivation of the herbicide ioxynil by contact with soil has been investigated. Shaking solutions of the sodium salt with acid soils led to a precipitation of the herbicide. With alkaline soils, a small amount of ioxynil became adsorbed on the soil particles. With unsterilized soils, hydrolysis to 3,5‐diiodo‐4‐hydroxybenzoic acid occurred, with 3,5‐diiodo‐4‐hydroxy‐benzamide as an intermediate product. Liberation of iodide ion in this system was also demonstrated.The phytotoxicity of ioxynil is enhanced by exposure of treated plants to light. The reduction in chlorophyll level of bean leaf tissue treated with ioxynil and other dihalogenohydroxybenzonitriles when exposed to light has been determined. Evidence is presented showing that although ioxynil is poorly translocated in the dwarf bean plant, its degradation products appear in the shoots of these plants after the herbicide has been supplied through the roots.