Warriors failed to turn possession and territory into points in Limerick on Saturday, suffering their second successive Pro12 defeat as the home side ran in three counterattack tries – two of them long-range solo scores.
Townsend said: "That was our poorest performance of the season – by a distance. We dropped off tackles and we stepped off Munster.
"We said beforehand that we had to make sure we put pressure on them and we did the opposite." Glasgow next host Townsend's former side, Castres, in the Heineken Cup on Friday.