green cancer

For this reason, it is frequently called the "green cancer" on the island.

Hammocks and clothing became damp, then sodden; mildew grew fast, like an odorous green cancer, fed by the humidity.

Surely someone from NUMA must know about the undersea plague that is spreading through your oceanic realm like a green cancer."

It is often referred to as the "purple plague" or the "green cancer" in reference to its habit of overgrowing native ecosystems, and its leaves which are bright green above and bright purple below.