For Double Bladed throwing weapons use Deathstalker or Toxic mod for the rank 3 or rank 4 Poison. Also keep a Fire Weapon because the Poison will also work as a accelerant allowing you to set Zombies on fire doing more damage.

Wait for the Zombies to throw up with Poison while they are throwing up poison hit them with a Fire elemental weapon to instantly set them on fire.

When you throw a poison weapon at a Ram the Ram will start randomly kicking in different directions while poisoned switch to a Fire elemental weapon and instantly set them the Ram on fire.

Poison + Fire is a good Combo