blister rust

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of several diseases of certain pine trees caused by fungi of the genus Cronartium, resulting in conspicuous blistering, dieback of affected areas, and often death of the tree.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun fungus causing white pine blister rust and having a complex life cycle requiring a plant of genus Ribes as alternate host
• noun any of several diseases of pines caused by rust fungi of the genus Cronartium and marked by destructive invasion of bark and sapwood and producing blisters externally