Coverage Issues Causing Poor Palmer Amaranth Control With Gramoxone


   There have been some Gramoxone burndown applications that have left some Palmer amaranth survivors. This happens to some extent every year. The cause of the problem is almost always coverage.
   Palmer amaranth female plants will often leave tens of thousands to hundreds of thousands of seed in relatively small areas in the fall. Palmer seed from these heavy seed rain areas emerge over a period of days this time of year. When fields are burned down, the Palmer that had emerged earliest in the field may be 8 to 12” or more tall. These taller weeds will cover the 1 and 2” Palmer that emerged later. These smaller covered ones are the ones that escape.
   Some ask about increasing the rate of Gramoxone.  Gramoxone at the 48 oz/A rate is sufficient. What needs raised is the gallons per acre.  Use a minimum of 15 GPA. In fields with heavy pressure consider bumping it up to 20 GPA.
   Finally, consider the nozzles used to optimize Palmer amaranth control.  Use nozzles that provide good coverage. Specifically, do not use nozzles that produce droplet sizes larger than a Spraying Systems AIXR or Wilger MR. Examples of nozzles to avoid with Gramoxone would be Spraying Systems AI and TTI or Wilger DR and UR nozzles. Also in very thick pigweed situations better control can often be attained by moving to a dual fan nozzle. ∆
   DR. LARRY STECKEL: Extension Weed Specialist, University of Tennessee
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