The absences forced coach Mick Potter to name rookie debutant Lee Gaskell, 19, at stand-off, with Jon Wilkin back in the side at scrum-half alongside him after a 12-match injury absence.
Three forward drives produced a scrum and the home side unleashed a wave of attacks which eventually saw Barnard just burrow his way over in the corner for a try awarded by the video referee.
Irish then saw substitute Dan Murphy sin-binned for pulling down a scrum with the home side camped just five metres from their line, and Dickinson put them out of their misery when he rumbled over at the death.
