2024 rules reference for Staff of Withering.
Staff
This staff has 3 charges and regains 1d3 expended charges daily at dawn.
The staff can be wielded as a magic Quarterstaff. On a hit, it deals damage as a normal Quarterstaff, and you can expend 1 charge to deal an extra 2d10 Necrotic damage to the target and force it to make a DC 15 Constitution saving throw. On a failed save, the target has Disadvantage for 1 hour on any ability check or saving throw that uses Strength or Constitution.