Free growing Poisons?

[Legbreaker]

The problem with poison is that they're not a very good combat weapon - they're just too slow on the whole (with a few rare exceptions).

Slipped into somebodies morning coffee an hour or two before a big fight on the other hand and they're great "equalisers", but on weapons?

Perhaps a knife coated in something caustic which while not necessarily poisonous, will cause a lot of pain in a wound would be useful. Siege weapons flinging poison gas canisters, or even the old standby, a few dead cows, could be useful in a long, protracted encounter...