DENVER (AP) -- Federal scientists say an exotic fungus spreading through Rocky Mountain forests is threatening Colorado's oldest trees -- the gnarled limber and bristlecone pines that can live longer than 2,000 years.

The white pine blister rust fungus, which spread from Asia, has attacked hundreds of those trees on national forest land in Colorado and in the Great Sand Dunes and Rocky Mountain national parks.

There is no known cure for the fungus, which penetrates pine needles, then covers branches with clamshell-shaped cankers and orange pustules, eventually girdling tree trunks. U.S. Forest Service scientist Anna Schoettle and other researchers are trying to find ways to slow the spread of the fungus.

The fungus is also threatening whitebark pine trees in Wyoming, Idaho and Montana.

Copyright 2010 The AP.