Adjuvants for Burndown Herbicides

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

I have had a few questions about burndown herbicides this year and many of the questions have centered around appropriate adjuvants.  Adjuvants are used to increase the surface contact on the leaf and increase herbicide penetration into the leaf. Selecting an adjuvant to avoid crop injury is not a concern for burndown herbicides, however, it is a consideration when spraying emerged weeds after the crop is up. The table below lists the common burndown herbicides and the recommend adjuvant(s).  It is important to use the correct adjuvant to maximize herbicide performance. When tank mixing herbicides with different recommended adjuvants use the more aggressive option.  For instance, when tank mixing Sharpen with glyphosate, use methylated seed oil.  Most glyphosate formulations have a built-in adjuvant system and no additional product is needed.  However, when tank mixing with Sharpen or Reviton, methylated seed oil is required.

Weed control with Gramoxone (and other paraquat formulations) is improved with the addition of metribuzin or atrazine. At this time of year, including either herbicide is important for achieving the highest level of control.

Liberty is not included in the list below because it requires intense sunlight for maximum effectiveness. The light intensity during burndown applications is typically not high enough to ensure consistent control.

Finally, using an adjuvant does not mean herbicide rates can be lowered. Always use the recommended rate along with the recommended adjuvants to achieve optimal weed control. Cool weather, changing weather patterns, and low soil temperatures can all limit herbicide performance. Do not further reduce burndown weed control effectiveness by lowering rates or using less effective adjuvants.