Last summer, the University of Tennessee talked about how application time of day (TOD) can effect more herbicides than just Liberty (link here). Initial results indicated that for Flexstar, Blazer, and Cobra applications made in the middle of the day were more effective than applications made at sunrise or sunset. Over the winter, we have been further investigating this concept in the greenhouse.

The test in the greenhouse was arranged similarly to the field trial. Flexstar (16 oz/A), Ultra Blazer (16 oz/A), and Cobra (10 oz/A) were applied with 1% MSO at 15 min prior to sunrise, noon, and 30 min after sunset. The application was made at 15 GPA with AIXR nozzles. Greenhouse conditions were maintained to reflect environmental conditions found in early summer in west Tennessee (day length=15 hrs, temperature=75-100ºF).

Results followed a similar pattern to that observed in the field. Palmer amaranth control suffered when each of these herbicides was applied in the morning vs. applications made at noon.  As with the field test the sunset applications did not provide the level of Palmer amaranth control compared to the noon application; however it was better than the morning timing (Time Lapse Video below). The most conspicuous difference in TOD effect was with Ultra Blazer (60% morning vs. 95% noon); however, Flexstar, was also significantly affected (60% morning vs. 85% noon). Although there seems to be a trend towards a similar type of effect with Cobra, it is not as significant as what we have seen with Blazer or Flexstar.

As the planting season nears, it is important to keep these herbicide characteristics in mind. Maximizing herbicide efficacy on Palmer pigweed is imperative to staying ahead of this weed and maintaining clean fields. Of course, weather conditions will play a part in when applications can be made and getting across large acreages timely will too.  Also, where applicable, consistency and efficacy from any of these herbicides is greatly increased when they are applied in combination with Liberty. A big thanks goes to Ginger Rowsey for the technical assistance in this video.