Century-old Salem trees hit with spreading fungus

Multiple black walnut trees on the Oregon State Hospital campus and nearby streets are infected with a newly discovered fungus that kills the trees from the inside out.

"They're going to die, and that's very sad," said Dan Hilburn, director of plant programs for the Oregon Department of Agriculture.

Thousand cankers disease is likely to spread further in Salem, Hilburn said.

"The public is likely to notice black walnut trees declining over the next five to 10 years in this town, and we'll lose our black walnuts," Hilburn said. "Big trees like that when they die – it leaves a big hole in the neighborhood."

Thousand cankers disease is caused by a fungus spread by tiny twig beetles native to the Southwest.

There, the beetles live on the Arizona walnut without causing any damage.

Here, they've adapted to black walnut, which is used as a street tree in Salem and across the West.

The disease was discovered a decade ago in Boulder, Colorado, when hundreds of the city's black walnut trees died. It took until 2008 to identify the fungus.

"The fungus is new to science and it's causing a new disease on a new host," Hilburn said.

In the West, it's since been detected in California, Oregon, Idaho and Utah.

The beetles likely spread through people moving the wood for lumber or firewood, or, as plantings grow closer, they simply fly from tree to tree, Hilburn said.

The real fear, Hilburn said, is that the disease will make its way to the East Coast, where black walnut is grown commercially.

Less than 2 percent of Salem's trees are black walnut, Jan Staszewski, the city's urban forester, estimates.

This is the first major outbreak in Salem, although Staszewski says he's seen a few isolated incidences in trees that already were in decline.

The fungus kills by causing cankers to develop around every location where beetles attack.

"Underneath the bark you'll have these dead patches that are dark," Hilburn said. "When you have thousands of them, the dead places coalesce. The sap just can't move in the tree anymore. Pretty soon, the poor tree dies from the top down."

Hilburn noticed the signs in the Oregon State Hospital trees a few years ago.

"This year, pretty suddenly, they look horrible," he said. "If you drive down Center Street and look up, their tops are dying."

Hilburn notified the Oregon Department of Administrative Services, which owns the hospital trees. The street trees are owned by the city.

One tree, in front of the old hospital building, already is scheduled for removal, DAS spokesman Matt Shelby said.

The state will prune the other trees, but not remove them until they are two-thirds dead, Shelby said. A number of trees currently are about a third dead.

tloew@statesmanjournal.com, (503) 399-6779 or follow at Twitter.com/SJWatchdog