Unripe White Hazel berries.
White Hazel is the most potent defense against Fairies. Its commonly used in Irish folk tradition when travelling at night and in Mythology it was used as a symbol of protection for messengers travelling between territories.
Unlike other cultures fairies Irish fairies are human sized and as much as they can help you they can also be lethal. The Hazel is such a potent symbol of protection it can protect the traveller from the most deadly of all manifestations of the Fairies The Black Pig. Even a look from the Black Pig can Kill, but in folk tradition if you beat the pig off with the Hazel stick it will run away.