First test any of these procedures on a spot that doesn't show. Lay clothing flat and pour salt on the stain, kind of thick then pour lemon juice on it let it sit for 30 minutes, then rinse. Or try white vinegar on the stain for a few minutes.
The two best things I have found for this are Oxy Clean and DD7, both are found at stores such as Wal-mart, Kmart, and drug stores. Just follow the directions on them for stain removal in fabrics and it should do the trick.