Dissipation and phytotoxicity of dicamba residues in water

By: C. J. Scifres, T. J. Allen,　C. L. Leinweber and　K. H. Pearson

The herbicide, 3-6-dichloro-o-anisic acid (dicamba), dissipated most rapidly from water under non-sterile, lighted conditions. Pond sediment evidently contained microbial populations capable of decomposing the herbicide. Temperature was crucial in dicamba dissipation, especially in the presence of sediment. Influence of sediment on dissipation rate of dicamba was apparently augmented by light in some cases. Under summer conditions, dicamba at 4.4 kg/ha per surface area of ponds dissipated at about 1.3 ppm/day. Dicamba dissipated as a logarithmic function of concentration with time. Reaction of seedling crops to irrigation water containing dicamba varied among species and cultivars. Relative tolerance from these studies was ranked from most to least tolerant as follows: sorghum [Sorghum bicolor (L.) Moench. ‘RS-626’ and ‘Pioneer 820’] > cotton (Gossypium hirsutum L. ‘Blightmaster’ > ‘Paymaster’ > ‘Dunn’) > cucumbers (Cucumis sativa L. ‘Straight eight’).


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