How do I fight ermor?

[Taqwus]

Pikes may do for a while. You can't repel a Wailing Lady's wail (length 6, area 1, save or die!), however, and undead archers may attrit you via the decay effect, and IIRC Behemoths will ignore the repel as well due to having incredible morale. A set of Behemoths can breach a line fairly quickly.
You'd also want to patrol sufficiently to keep out the Harvesters and, say, Black Servants with Bane Venom Charms.