Time Your Herbicide Applications for Maximum Control

The time of day when you spray Palmer amaranth greatly influences the efficacy of the herbicide treatment. That’s the finding from a concentrated, multi-state research study. Researchers from the University of Georgia, North Carolina State University, Louisiana State University, Mississippi State University and the University of Tennessee worked together to produce the study.

  • Liberty herbicide sprays were more effective when application was delayed until at least 2 hours after sunrise.
  • Results suggest the time of day effect may be partly due to reduced translocation of the herbicide when applied at night or at sunrise.
  • The time of day of application affected Liberty herbicide efficacy the most. One study recommends that Liberty should be applied in the Southeast and Midsouth from two hours after sunrise through one hour before sunset for most optimal control of Palmer amaranth.

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Stanley Culpepper, Professor and Extension Agronomist, University of Georgia was a key driving force in completing the large, multi-state study. And while the researchers are learning more about how herbicides react to applications at different times of the day, they have a lot more to learn about “why.” “I had a lot of complaints (about Liberty) that I could not figure out,” he says. “One day we were literally spraying (Liberty) at the crack of dawn, and it didn’t work. I went back to the complaints and it was always when it was applied very early in the day. I started connecting the dots. I don’t know that we have the answers yet – could it be translocation? It’s not clear.” The goal, according to Culpepper, is helping growers optimize product efficacy and get the best return on investment from their herbicides. “You really want to figure it out so you can help your growers  – that’s what it’s all about,” Culpepper says. “It’s all about maximizing control. Keep in mind that, in Georgia, our cotton industry alone has spent over $1 billion in controlling glyphosate-resistant Palmer amaranth since its first discovery. “We need to maximize every single approach every time we do it. It’s the difference between somebody making money and not making money on a field. I have to spend my time maximizing every aspect of their weed management system. That’s why we’re looking at time of application, to make that as effective as possible.” Click here to see more info.

Click Table to Enlarge.Time of Day to Spray Pigweed?, Nochaway Ag Update, University of Georgia Extension

  To see more data from the studies and download the abstracts, click here.