Glowing Pearl of Malady

[Magnas119]

Description says that it increases disease damage by 80 percent.

After buying and testing it is not increasing disease but instead is activating on poison spells.

[Nerva]

Disease and poison damage augments are reversed: Disease focii affects poison spells, poison focii affects disease spells. It's a long-standing bug that annoys your average Necromancer to no end, and irks SKs, Shamans, and Druids too.

Coupled with spell availability, it's a big reason why your average necro sticks with fire and magic DoTs.