Tips On Chemical Termination of Cover Crops

  • Do not apply either glyphosate or Gramoxone unless daytime temperatures exceed 55-60°F.
  • The higher the temperature the better.
  • Cold nights (<40°F) will reduce activity, particularly for glyphosate.
  • Sunny weather is important for Gramoxone as sunlight causes greater plant activity.
  • Be sure to include AMS at 8.5 to 17 lb/100 gallon or equivalent with glyphosate and add a good quality NIS at a 0.25% v/v to Gramoxone. Of course, if the glyphosate doesn’t come fully loaded, add good quality NIS as well. Always add the AMS first as it also conditions hard water.
  • Nitrogen solutions (UAN) may be used as the carrier with either herbicide. UAN can increase Gramoxone activity and reduce Glyphosate activity (especially for perennials and difficult to control weeds). Adding AMS also reduces the antagonism.
  • Tank mixing a triazine such as atrazine with Gramoxone increases the activity; tank mixing any other herbicide and especially a clay-based herbicide (DF, F, WP) reduces glyphosate activity. You can overcome the antagonism by increasing the glyphosate rate by 20 to 25%.
  • Use flat fan tips with both (not floods) and apply Gramoxone at a minimum of 20 GPA. Tip selection is less important with glyphosate than Gramoxone.
  • Spraying in late afternoon is not as effective as mid morning.
  • Finally, spray weeds that are actively growing and the smaller, the better for annuals.

Contact Information

William S. Curran
  • Professor of Weed Science
Phone: 814-863-1014