Scientists’ fears were realized in 2004 when pitch canker, a devastating disease threatening Monterey pine Christmas tree lots, landscape plantings and native coastal forests in 19 California counties, spread into the Sierra Nevada.

The development underscores the importance of prompt and proper Christmas tree disposal after the holiday.

The pitch canker fungus, Fusarium circinatum, was isolated from a tree in a Douglas fir breeding orchard at the 1,000-foot elevation near Placerville in El Dorado County. Before this discovery, pitch canker in California was known only in counties on or near the coast.

"Surveys suggest that it remains an isolated infestation, so there is still good reason to be concerned about introductions to uninfested areas," said Tom Gordon, UC Davis plant pathologist.

Infected Christmas trees have been found in San Mateo, Los Angeles, Orange and San Diego counties at choose-and-cut tree lots. To help prevent the spread of pitch canker to the Sierra Nevada, scientists recommend that no Monterey pine or other pine firewood, cones, logs and chipped pine material be transported from west of Interstate 5 to east of Interstate 5. The state has also designated a "Zone of Infestation," which counties may use to place restrictions on the movement of potentially infested materials.

"People can buy healthy-looking trees that are infected with pitch canker. If they are left for a long period in the backyard, insects could visit and spread the disease to landscape pines," Gordon said. He suggests all Christmas trees be promptly turned over to community recycling programs, or chipped and spread as a thin mulch, or composted.

Pitch canker was first discovered in the pine plantations of the southeastern United States 60 years ago. The disease was not known before that anywhere in the world. In the Southeast, pitch canker was not much more than a curiosity until the mid-1970s, when it became a serious problem on slash pine.

In 1986, foresters found pitch canker in California. It quickly developed an association with native insects and spread to many native pines, including Monterey pine, Bishop pine and knobcone pine. Infected trees in landscape plantings and native forests are found in coastal areas from San Luis Obispo to Mendocino counties.

While young Monterey pines are bushy and can be shaped into a cone for Christmas, mature Monterey Pines grow 50 to 100 feet tall, are often multi-trunked and carry all their vegetation high in tufts.

Monterey pines are greatly prized for their esthetic value in the three California locations that comprise the only native populations of Monterey pine on mainland anywhere in the world. Stands are found at Año Nuevo in San Mateo County, on the Monterey Peninsula and near the quaint coastal town of Cambria.

"All those populations became infested with pitch canker and are still today," Gordon said. "Although the situation from a statewide perspective has more or less stabilized, on a local scale, it is becoming more severe."

Gordon’s research at UC Davis has determined that gray pine, coulter pine, Torrey pine, ponderosa pine, shore pine and Douglas-fir are susceptible to pitch canker when they are exposed to the disease in growth chambers.

Gordon and UC Berkeley entomologist David Wood have found some Monterey pine trees to be naturally resistant to pitch canker and some trees observed over many years have only a very limited amount of damage caused by the fungus. These trees are not expected to die from the disease unless new strains of the fungus are introduced into the state and are able to overcome the natural levels of resistance. The scientists believe that where young trees are exposed to pitch canker, many of those that survive will be resistant.

For that reason, they say natural regeneration is the first choice for pitch canker-infested forests. Monterey pine, Gordon said, regenerates best after fires. However, since prescribed burning is not an option for these highly populated areas, Gordon and his colleagues are conducting studies to determine whether mechanically removing or incorporating vegetation in the forests will improve Monterey pine regeneration.

UC scientists are also working with landscape specialists at Asilomar State Beach and Conference Grounds and at Pebble Beach Golf Links, both on the Monterey Peninsula, to take a proactive approach to Monterey pine regeneration.

"The landscapes are carefully managed at these facilities. The staff is actually screening seedlings as they grow up to see what looks resistant before they are planted,' Gordon said. "We provided them with the methodology, gave them the inoculum and helped them get their programs established."

There is a similar program at the Presidio in San Francisco, where arborists have now replanted one area with trees generated from rooted cuttings of trees on their property that UC identified as resistant to pitch canker.


Media Contact: Tom Gordon, (530) 754-9893, trgordon@ucdavis.edu (Gordon will be available for interviews Dec. 13-23.)