Douglas-fir trees are cunning carriers of pitch canker disease

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May 1, 2007
Douglas-fir trees are cunning carriers of pitch canker disease

Like stealthy predators, Douglas-fir trees can harbor the pathogen responsible for pitch canker disease for a year without showing any symptoms and pass it off to other susceptible species.
Pitch canker infection on a Monterey pine branch showing resin that is typical of the tree's response to the pathogen.


Pitch canker infection on a Monterey pine branch showing resin that is typical of the tree's response to the pathogen.
Photo by Tom Gordon

This insight discovered by UC Davis plant pathologist Tom Gordon can help to manage the disease in landscape settings, Christmas tree farms, and in commercial forestry.

"Pitch canker fungus readily colonizes Douglas-fir trees," says Gordon. "The growth is usually so limited that no visible damage results, and in that sense, there is no disease. However, the fungus can produce airborne spores while growing on Douglas-fir, and these may be carried by the wind, or by insects, and eventually reach host plants that are much more prone to damage. This knowledge underscores the importance of limiting movement of Douglas-fir and other hosts from infested to uninfested areas.

Pitch canker, caused by the fungus Fusarium circinatum, was first discovered in the southeastern United States about 60 years ago. Before that, the disease was not known anywhere in the world. In 1986, foresters found pitch canker in California. Since its discovery in California, the disease has spread rapidly and now occurs in 18 California coastal counties.

Most pines native to California are susceptible to pitch canker, but Monterey pine is the most widely affected host. Some Monterey pines, however, are unaffected by pitch canker, even when they are surrounded by severely infected trees because they have a wide range of susceptibility to the disease.

The appearance of pitch canker in ornamental plantings of Douglas-fir and ponderosa pine trees has raised concern that native and commercial stands of these species in the Sierra Nevada may become impacted by the disease.

To date, the Sierra Nevada has been spared. "Testing has shown no evidence that the pathogen has developed an association with pine-feeding insects in the Sierra Nevada, and this may be why pitch canker has failed to become firmly established in this area," says Gordon.

Currently, Gordon is taking a look at the possibility that the pathogen could adapt genetically to overcome geographic limitations presently imposed on pitch canker by environmental conditions and host resistance.

"Because the fungus can reproduce sexually it's possible that it may adapt to lower temperatures and expand its range northward along the California coast. Likewise, it could generate new pathogenic forms capable of causing disease on trees that presently manifest resistance."

For more information about pitch canker disease, visit the UC Statewide Integrated Pest Management Program Web site.
Resources

High-resolution image (468KB) "Pitch canker infection on a Monterey pine branch showing resin that is typical of the tree's response to the pathogen." Photo credit: Courtesy of UC Statewide IPM Program, by Tom Gordon. Photos are for use with this release only. All other uses see Legal Notices.

Pitch Canker Pest Note.
Contacts

Stephanie Klunk, Communications Specialist
UC Statewide IPM Program
(530) 754-6724

Tom Gordon
UC Davis
(530) 752-4269

The UC Exotic/Invasive Pests and Diseases Research Program targets research on exotic pests and diseases in California. The program aims not only to improve our knowledge and management of pests that are already here, but also to reduce the potential impact of those pests and diseases that pose a threat to the state. The program is a collaboration between the UC Statewide Integrated Pest Management Program and the UC Riverside Center for Invasive Species Research. U.S. Department of Agriculture, Cooperative State Research Education and Extension Service, funds the program.

Statewide IPM Program, Agriculture and Natural Resources, University of California
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