Submitted to: Proceedings of Southern Weed Science Society
Publication Type: Abstract Only
Publication Acceptance Date: 1/25/2000
Publication Date: 1/25/2000
Technical Abstract: Previous field studies have shown that pyrithiobac efficacy evaluated over 2 growing seasons on the Texas Southern High Plains was correlated with air temperature at the time of application (R^2=0.90). Based on these studies, a temperature-based recommendation that provided >90% reduction in dry weight 14 days after postemergence pyrithiobac applications was created. This thermal-based recommendation suggested that postemergence pyrithiobac applications be made when air temperatures are 20-34C. However, the potential utility of this recommendation to producers has not been examined. The objectives of this study were to determine the probability, frequency, & duration of the temperature-based postemergence pyrithiobac application range, & investigate the utility of using computer visualization to convey the significance of postemergence pyrithiobac efficacy thermal dependence Historic air temperature data sets collected over 11 growing seasons were analyzed. The recommended thermal range occurred during 59-93% of the daylight hrs in a typical growing season. Conversely, up to 41% of pyrithiobac applications might be adversely affected by application temperature. In some years, the temperature exceeded 34C on more than half the days evaluated for more than 6 hrs. Long durations of temperatures exceeding 34C provide a narrow window for applications. However, the duration of temperatures below 20C was generally <2 hrs. Cooler temperatures predominantly occurred in the early hours of the morning, increased, & remained within range for several hours. Therefore, delaying application until the minimum temperature was reached could allow producers to obtain acceptable weed control.