High Temperatures Are Required for Expression of Metabolic Resistance to Cyhalofop-Butyl in a Biotype of Echinochloa crus-galli

Rising average global temperatures due to climate change may affect weed survival to herbicides. The metabolic resistance of Echinochloa crus-galli to cyhalofop-butyl was characterized at 25/20 °C and 35/30 °C. The biotype SAOJER-R was resistant at 35/30 °C with GR50 > 525 g ai ha-1 but was susceptible at 25/20 °C with GR50 -1. SAOJER-R biotype needed at least 48 h of exposure to 35/30 °C after application to express the resistant phenotype. The resistant biotype metabolizes cyhalofop-butyl and acid faster than the susceptible, and faster at 35/30 °C than at 25/20 °C. The application of a cytochrome P450 monooxygenase inhibitor with cyhalofop-butyl increased the amount of active herbicide recovered in plants at 25/20 °C. Seven cytochrome P450 monooxygenase, seven glutathione-S-transferase, and five UDP-glycosyltransferase genes were upregulated. Temperature is critical for expression of SAOJER-R metabolic resistance to cyhalofop-butyl at label rate. We suggest that temperature conditions should be standardized when evaluating metabolic herbicide resistance.