To be able to summon Putrid Wraith I have to invest skill points into Noxious Blades node. However it turns out that the node grants posion chance on melee hit, but Putrid Wraith is caster.
There is another node - Serrated Scythes that grants bleed damage chance for melee and spell attacks. I would like to propose to grant to Noxious blades poison damage chance on hit, i.e. to support spell attacks as well.