Sulfentrazone is a herbicide that has been observed to injure crops in an unpredictable manner. Therefore, experiments were conducted to determine whether root absorption of sulfentrazone was dependent on the pH of the rooting medium. Studies were initiated to examine sulfentrazone uptake of whole plants from soil and hydroponic solution, as well of excised roots in solution. These experiments demonstrated that transpiration decreased as soil pH decreased and herbicide rate increased; it was our intention to use this measure as a description of herbicide injury. Likewise, plants grown for 24 h in ¹⁴C-sulfentrazone hydroponic solution accumulated a greater herbicide concentration in roots as solution pH decreased below 6.5. This trend of increased absorption with reduced solution pH was again demonstrated when excised cotton roots were placed for durations of 10 to 120 min in hydroponic solution containing ¹⁴C-sulfentrazone. However, when excised roots were placed in solution containing the weak acid herbicide glyphosate, no trend of increased absorption was observed with changes in solution pH. Therefore, it was concluded that the accompanying change in solubility, as sulfentrazone was converted from the ionic to the neutral form, was responsible for the increased absorption by plant roots. Localized differences in soil pH could be responsible for greater sulfentrazone uptake and explain the unpredictable patterns of injury that have been observed.

Nomenclature: Glyphosate; sulfentrazone; cotton, Gossypium hirsutum L. ‘Fibermaxx 989 RR/BG’; tobacco, Nicotiana tobacum ‘TN 90’, ‘KY 14’.