Green’s Dictionary of Slang

peacher n.

[peach v. (1)]

an informer.

Fox Martyrs n.p.: Accusers or peachers of others that were guiltless [F&H].
[UK]B.E. Dict. Canting Crew n.p.: Whiddler, a Peacher (or rather Impeacher) of his Gang.
[US]Wood & Goddard Dict. Amer. Sl. 38: peach. To inform or tattle-tale upon. Hence, peacher.