Dale skipper Gary Jones scored the 17th goal of a prolific campaign after 49 minutes to leave Argyle at the foot of the League One table.
Plymouth, six points adrift of safety, came closest when Yannick Bolasie thumped a header against the woodwork after 29 minutes.
"I always thought that one goal would probably decide it and unfortunately that's the way it turned out," Reid said.
"Yannick has hit the post for us and we had one or two efforts cleared off the line and then Rochdale scored the goal early in the second half.
"Now we have eight games left and they are massive games. It's not a great league table for us at the moment. It looks a bit grim."
Source: PA
Source: PA