Plants on the surface of Arides. (COMIC: The Emissaries of Jevo)
Arides was a planet that was home to a species of flowering plants, the pollen of which was deadly to all human and animal life. At some point, these plants mutated into a giant form. If they flowered they would spread the pollen through space, destroying life on all planets in the universe.
To prevent this, the people of Jevo sent an expedition commanded by Kirid to Arides to spray the plants with poison. The mission was successful, but at the cost of the Jevo ship, which was destroyed by the Daleks. (COMIC: The Emissaries of Jevo)