"The extermination of the Undrea's blight upon the Acarhyn lands has ended!"
Huh?
Maybe...
"The extermination of the Undrea has ended this blight upon the Acarhyn lands!"
or
"The extermination of the Undrea has ended it's assault upon the Acarhyn lands!" (maybe rampage or attack? "Blight" doesn't really fit a large monster tearing stuff up)