The effects of 2,4-D iso-octyl ester/ioxynil herbicide in the liquid and vapour phases on the growth of tomato (Lycopersicon esculentum Mill.) plants

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Abstract
Controlled-environment studies confirmed that tomato plants subjected to a range of treatments involving the herbicide 2,4-D iso-octyl ester/ioxynil applied in the vapour and liquid phases develop symptoms of phytotoxicity in proportion to the severity of the treatment. Plants which received direct foliar applications of herbicide emulsion (40 μg, 100 μg and 1 000 μg per plant) failed to survive longer than 35 days. In contrast, none of the plants subject to vapour treatments were killed as a consequence of herbicide activity in the vapour phase. Vapour treatments were, however, associated with a variety of sub-lethal plant responses which included changes in plant height, dry matter content and abnormal leaf development. Flowering was advanced by some herbicide treatments. The lower stems of many treated plants also developed root primordia and in the case of the more severe treatments, lesions of the stem occurred. Symptoms of phytotoxicity from which many plants recovered included apical stem bending and downward curving of the leaves and leaf petioles. An examination of the associations between the development of visual symptoms of phytotoxicity and measurable plant growth responses (height and dry matter yield) have been used to develop a diagnostic base for the identification of auxin-like herbicide damage in field-grown plants.