Some recent research by a former AHRI researcher Jingbo Li and others shows that glyphosate resistance changes this. They studied two populations of barnyard grass with relatively low-level glyphosate resistance and found that when 2,4-D Amine or Ester was added to the tank with glyphosate, barnyard grass control was greatly reduced. They went on to discover that this is due to an effect on uptake and translocation.