From Zuckerman:
T o make room on the active roster for Werth, the Nationals placed reliever Henry Rodriguez on the 15-day DL with a back injury. Manager Davey Johnson said he was ready to option Tyler Moore to Class AAA Syracuse so the first baseman/outfielder could get regular playing time again, but Rodriguez had been getting treatment on his back for a while and was deemed injured enough to place on the DL.