Tennessee Granted Brake F2 Label For GR Palmer Amaranth Control In Cotton


   Tennessee just received a Section 18 label (Brake F2 Label) for the use of Brake F2 (fluridone + fomesafen) for control of glyphosate-resistant Palmer amaranth in cotton. There has been quite a few questions this week on Brake after the Section 18 was approved and I will attempt to answer some of them below:
   First off a little history of how Brake F2 got to this point. Fluridone is not a new herbicide. It was first developed back in the early 1970s at the same time as its cousin, Zorial (norflurazon). Back then both herbicides were candidates to be used in cotton.  Zorial was chosen at it was better on the weed spectrum at the time and was cheaper to produce.  Fluridone went into the aquatic market and is still used there today under the trade name Sonar. However, some folks remembered it had good pigweed residual back then which led to research over the past couple years of how it might fit in a cotton weed control program.
   The first thing we did in 2012 was to start looking at rates much lower than the 0.5 lbs plus fluridone rates looked at back in the 1970s. We did this for a couple of reasons. The first was to reduce the cost and the second was to limit re-crop concerns. What we found in 2012 was that fluridone could provide 4 weeks of residual Palmer amaranth control at rates at least as low as 0.2 lbs/A. We also found that fluridone is a very safe cotton herbicide. On the negative side, we found that fluridone needs a good 0.75” of precipitation to become activated. In fact, because of the dry spring in 2012, fluridone took many weeks after application to activate in research trials across the south. As you can imagine the pigweed control was poor compared to the standards of Cotoran or Reflex (fomesafen) that needs very little rainfall to activate.
   The folks at Sepro, who manufactures fluridone, addressed the activation problem by putting together a premix of fluridone + fomesafen (Brake F2). The idea is that fomesafen needs very little water to be activated and as such could provide residual pigweed control until the fluridone becomes activated.  The hope was that this product would provide much more consistent results. That was the case in 2013 in research across the south. Based on these results as well as the desire to get another effective herbicide mode of action on pigweed into the mix, it was decided to apply for the Section 18 label.
   Brake F2 can be applied pre plant to preemergence under this Section 18 label.  The going rate most will use is a pint per acre. That pint rate will provide 0.2 lbs of fluridone which is a bleaching type herbicide (Group 12) and 0.125 lbs of fomesafen herbicide (equivalent to 8 oz of Reflex). The re-crop interval back to soybean or wheat after the pint rate of Brake F2 is 4 months and plant back to corn is 6 months.
   Though it can be applied pre emergence, the most consistent pigweed control will likely come from application 1 to 2 weeks before planting. This increases the probability of an activating rainfall for the fluridone as well as working the fomesafen into the soil which should decrease the probability of cotton injury from that herbicide. Another good use of this herbicide is in irrigated fields where the grower is willing to cut the pivot on to get the Brake F2 activated.
   This herbicide has some intriguing upside with the potential to provide good residual pigweed control.  On the negative side this herbicide is 2 to 3 times more expensive than the pre applied herbicides we typically use. In our research it had similar pigweed residual as tankmix of Cotoran + Caparol. However Brake F2 has provided longer residual than either Cotoran or Caparol applied alone and it provides another herbicide mode of action to control Palmer.
   We are clearly taking baby steps with the use of Brake F2 in Tennessee this year. There will only be about 7500 acres available in Tennessee. This will be the year to see how this herbicide might be integrated into a system to help manage pigweed both in small plot research and on some grower’s fields.  Depending upon how it performs this summer we can make the determination whether or not to adopt it more heavily.∆
   DR. LARRY STECKEL: Extension Weed Specialist, University of Tennessee
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