Feb 25, 2017· Answer Wiki. 2 Answers. Quora User, Nom, nom, nom... If the dry mustard is for a spice rub or other dry mix, horseradish or Wasabi powder in reduced quantities make reasonable substitutes as do crushed/ground mustard seeds. The pungency is likely to be a little stronger with horseradish powders and about the same with ground mustard seeds.