An infection among La Jolla’s Torrey pine trees is spreading rapidly.
A non-native fungal pathogen called fusarium circinatum, or pitch canker, has been damaging Torrey pines from La Jolla to Del Mar; no known treatment exists.
The pathogen was first noted around 2020, according to Darren Smith, senior environmental scientist for the California State Parks district that runs from Carlsbad south to the Mexican border.
The pathogen wasn’t concerning, Smith said, until it showed up a year later on a Torrey pine next to the Torrey Pines Golf Course, its spread confirmed in 2022 and beyond into a large portion of the Torrey Pines State Natural Reserve, where 1,500 acres of land serve to protect the Torrey pines.
It’s now spread throughout the reserve, around UC San Diego and up into Torrey pine trees in Del Mar.
The Torrey pine is North America’s rarest, only growing naturally along this part of the San Diego coast and on Santa Rosa Island off Santa Barbara. It’s estimated there are fewer than 3,000 of them left.
The pitch canker – which seems to only affect coniferous trees – is spread by beetles boring holes into the trees, Smith said.
Figure 8 from ‘The Pitch Canker Epidemic in California.’ by Thomas R. Gordon, A. Storer, D. Wood. Published in Plant Disease 1 November 2001. Several of the insect-mediated infection pathways that collectively represent the principal means by which pitch canker infections are established on susceptible pines in California. The trees, shown in the center of the figure, represent the typical progression of pitch canker symptoms.
Working with Cal Fire and the U.S. Forest Service, the State Parks Department has determined “anything that can puncture the bark and wound the trees is a likely carrier from tree to tree,” Smith said.
And I think by now, “the infection spread throughout the entire state natural reserve and much of the area, like I’ve seen it up in Del Mar, … throughout the whole population.
“There’s no real treatment” for the pitch canker, Smith said, adding a similar infection occurred in coniferous trees in Monterey about 20 years ago, with experimentation failing to find a reliable remedy.
The hopeful news, however, is it appears the Torrey pines have “some natural resistance” to the canker, he said. “We don’t know if that’s genetic or just circumstances, but some trees are [less] affected.”
No Torrey pines have yet died from pitch canker alone, Smith said. “I’m hopeful that the trees will hang in there and fight off the infection for the most part.”
Smith estimates about a third of the local trees are infected, though he acknowledges that number is “loose” and difficult to ascertain, as only a laboratory test can determine the presence of the pitch canker; it can’t be diagnosed just by looking.
The rapid spread throughout the La Jolla and Del Mar region indicates that residents with coniferous trees in their yards need to have an arborist evaluate them.
Some affected areas of a tree can be trimmed away to promote the tree’s heath, but Smith emphasized the importance of sterilizing the trimming tools immediately afterwards and to separate the infected wood from other coniferous populations to keep the fungus contained.
“Be real careful with what you do with the lumber,” Smith urged. “If you do trim … or cut down a tree, you want to keep it so that it doesn’t spread to other communities.”
