Thousand Cankers disease threatens walnut industry.

• Author: O'Meara, Carol
• Position: AGRICULTURE

When a tree falls in the urban forest, people hear the sound. And when one becomes hundreds, entire cities take note, and mobilize a coalition of forestry experts.

Thousand Cankers disease is attacking black walnuts, and cities from Pueblo to Longmont are suffering losses. Walnut twig beetles (Pityophthorus juglandis) carry a fungus, Geosmithia morbida, into branch and trunk, which the fungus kills with thousands of rotting wounds, called cankers.

"Slowly but surely, this is eliminating black walnuts here in Colorado," said Dr. Ned Tisserat, Colorado State University professor of plant pathology and disease discoverer. "It's hard to know the final outcome, but the real threat is outside our state, to...