A UC Davis scientist warns that Christmas trees should be recycled quickly and correctly to protect yard trees and wild forests from a deadly, spreading disease.

The disease, pitch canker, has been found in Christmas tree lots, landscape plantings and native coastal forests in 19 California counties. Infected Monterey pine Christmas trees have been found at choose-and-cut tree lots in San Mateo, Los Angeles, Orange and San Diego counties.

An infected tree may look healthy. But if one is left outdoors for very long, insects could spread the canker near and far. UC Davis plant pathologist Tom Gordon and colleagues have determined that many trees in the state's forests are susceptible to the disease, including gray pine, coulter pine, Torrey pine, ponderosa pine, shore pine and Douglas fir. Gordon is particularly concerned about pitch canker spreading to the Sierra Nevada.

"People can buy healthy-looking trees that are infected with pitch canker. If those trees are left for a long period in the backyard, insects could spread the disease widely," said Gordon.

Gordon urges people to send their Christmas trees promptly to community recycling programs. It's also okay to chip trees and put the chips in compost piles or spread them in the landscape as a thin layer of mulch.

No pine parts -- firewood, logs, chips or cones -- should be transported from west of Interstate 5 to east of Interstate 5.

Pitch canker, caused by the fungus Fusarium circinatum, was first discovered in the woody pine plantations of the Southeastern United States 60 years ago. The disease was not known before that anywhere in the world. In 1986, pitch canker was found in California.