Below is some comments and a table developed by our UGA Extension Weed Scientists that shows the effect that application time of day can have on herbicide performance on Pigweed:
Over the past few years, we have been studying the impact of application time of day on the postemergence activity of numerous herbicides. The table below is provided to help guide you in making timely applications. Liberty remains, by far, the most sensitive herbicide to the time of day in which it is applied. However, research is showing most herbicides applied early, late, or early and late may not perform at their optimum.
Consistent results from numerous locations have been generated with Liberty, Roundup, Clarity, and 2,4-D. For Reflex, Direx, and Gramoxone results provided are from a single location and the study will be repeated during 2015.
If you have any questions, contact your local county agent for more information.