Submitted to: Proceedings of Southern Weed Science Society
Publication Type: Proceedings
Publication Acceptance Date: 1/25/1999
Publication Date: N/A
Technical Abstract: Pyrithiobac is a preemergence and/or postemergence herbicide used in cotton (Gossypium hirsutum). In its three years of commercial use, inconsistent weed control has been observed in the field. This inconsistency may be influenced by environmental factors such as light, rainfall, and temperature. This study sought to obtain the kinetic parameters of acetolactate synthase (ALS) from Palmer amaranth, determine whether ALS sensitivity to pyrithiobac varied with temperature, and correlate enzyme inhibition with field efficacy. Results demonstrated that temperatures both above and below 30 degrees C showed decreased inhibition efficiency of ALS. Correlation with field efficacy was obtained by independently cultivating 16 plots of 5-10 cm Palmer amaranth and treating them with pyrithiobac. Plant/soil scene temperatures were monitored with Irt/c sensors and air temperatures were monitored with a thermocouple at a height of 1 m. Optimal lfield activity occurred at ambient temperatures of 20 to 34 degrees C. Comparison of field activity and enzyme inhibition indicated that both accumulated DW and the I_50 values increased rapidly above 34 degrees C. Therefore, the thermal dependence of the ALS-pyrithiobac interaction may contribute to variable activity observed in the field.