Effect of Soil PH on Fluridone Activity and Persistence as Determined by Chlorophyll Measurements

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Abstract
Residue levels of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} in soil were determined indirectly by measuring the chlorophyll content of wheat (Triticum aestivum L.) grown on a Norfolk sandy loam (Typic paleudult; fine loam, siliceous, thermic) 14, 22, 39, and 66 days after a preemergence application of the herbicide. The half-life for 0.22 and 0.45 kg/ha of fluridone was estimated to be 18 days. Phytotoxicity increased with increasing pH in newly-treated soils and in soil sampled 14 days after treatment. Higher chlorophyll levels in wheat grown in soil sampled 39 days after fluridone application indicated a decrease in biologically-active herbicide. Soil removed from the field following later cultivation produced small reductions in chlorophyll at pH 4.0 and 5.2, but at pH 7.0 significant fluridone activity was still present in the soil after 66 days. Cultivation may have increased the surface concentration of the herbicide.