Temperature Effect on Difenzoquat Phytotoxicity

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Abstract
The phytotoxicity of difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) applied to the three-leaf stages of hard red spring wheat (Triticum aestivum L. ‘Waldron’ and ‘Era’), barley (Hordeum vulgare L. ‘Beacon’) and wild oat (Avena fatua L. ♯ AVEFA) grown under constant, fluctuating, or alternating day-night temperatures was determined in controlled environment chambers. Difenzoquat injury to wild oat and Era wheat was greater at a constant 20 or 30 than at 10 C; however, injury to Waldron wheat was similar at 10, 20, and 30 C. Difenzoquat caused only slight injury to barley, and injury was similar at all temperatures. In Era wheat, selectivity of difenzoquat for wild oat was maximum with a 10-C night temperature in an otherwise 30-C-temperature environment; in Beacon barley selectivity was maximum with 3 or more days of 20- or 30-C posttreatment temperature; and in Waldron wheat selectivity was not adequate at any of the temperatures studied.