'Between you and me, if the Devil lent me his powers, I doubt I'd use them to cure farm wives of their monthly pains.'
Witch's Curse is a sidequest which can be started when you make one trade with Uallach. After you finished trading with her, she will ask you in which gods you believe. By selecting that you believe in the Norse gods, she will request you to take down the four remaining curse poles in Perth in order to protect her reputation.
One curse pole can be found near the place where the two Norsemen are captured from Just Deserts. It is on the other side of the path. A second pole can be found in a field with some cows near the smith. Taking this one down will get you in a battle with the locals who believe you mistakingly believe you are setting them up. The battle can be won easily by blocking the entrance to the cow pen with a tank and taking out the archer the first turn. Since they lack ranged weapons, expect for the archer, you can easily take them out this way. If you have diplomacy rank 4, you can talk your way out of this fight.
A third pole can be found west in the area near a pig pen. From the cross, go west and look near the trees.
The fourth curse pole can be found in the southwestern corner near a bonfire.
After taking down all curse poles, return to Uallach for your reward.