Death spores

Death Spores is a ship weapon in Master of Orion.

Description
Death Spores are genetically engineered, rapidly mutating viruses that relentlessly attack organic life forms. They are so contagious and deadly that invading ships must introduce them into the target planet's atmosphere by orbital bombardment. Each spore pod launched has a chance to kill one Population Unit. The use of biological weapons causes revulsion in all other races in the game, and your diplomatic status suffers accordingly.