Use the Scythe of Trials until the latent effect disappears.
How to remove the latent effect:
You must perform Weapon Skills and Skillchains on monsters that con Easy Prey or higher.
You receive 1 point for opening/soloing a weaponskill, 2 points for closing a Lv.1 Skillchain, 3 points for closing a Lv.2 Skillchain and 5 points for closing a level 3 Skillchain.
You must accumulate 300 total points.
To check to see if the latent effect has disappeared, simply unequip and re-equip the Scythe of Trials and if you do not get the elemental resistance bonuses, you are done.