In my years as an herbalist, I've often observed that nature will provide subtle cures to the most vexing of problems. I've read that hedge mages and witch doctors often use the smoke of an herb known as witchbane to draw evil from its hiding places.
If true, this would mean witchbane should be growing near the shadow waters of Witch Hill. You should be able to identify it by its broad leaves and reddish central stalk. Bring me any herb you can find, <name>. It may be our only hope.
Were you able to gather any of the herb? We must work quickly, before whatever evil is behind this infestation consolidates its hold on this area.
<Mordant accepts the bunch of herbs from you.>
These match the description exactly! I prepared the torch while you were out. All that remains is to fasten the herbs to the end here.