So you're takin the fight to the coven with the Waycrest girl, eh? Ya might just be able to take advantage of their apparent onion aversion.
While you're out rootin' in the field, keep an eye out for any onions bulging out of the ground. Those ones should be particularly aromatic, and should cause some fits in the coven's minions if you keep it on ya.
Just try not to take too much, right? I need enough left in the fields to keep the farm safe.