Fungus carried by beetle puts 4,000 of Denver's black walnut trees at risk; Denver, CO

Denver Daily - Fungus threatens black walnut trees
Gene Davis, DDN Staff Writer
Monday, July 20, 2009

The approximated 4,000 black walnut trees in Denver face a serious threat from a newly discovered deadly fungus.
Ned Tisserat, a plant pathologist at Colorado State University, discovered “thousand cankers disease” last summer. The disease has already devastated black walnut trees in Colorado Springs and Boulder and is believed to have been active in Denver for at least three years, according to Jill McGranahan, spokeswoman for Denver Parks and Recreation.
“It’s pretty serious — it can really affect the tree canopy in the city,” she said. “It’s pretty significant if we would lose all of them.”
Thousand cankers disease is carried to trees by a tiny twig beetle that is common in Arizona walnut trees. While the beetle isn’t harmful to the Arizona walnut trees, it causes a fungus in the black walnut trees. The fungus then colonizes and kills a small area of the bark surrounding the beetle galleries, said Tisserat.