Pine trees may not enjoy the popularity that oaks and some other local species do, but they’re still valuable components of Bay Area landscapes that provide shade, support local wildlife, and increase curb appeal. But unfortunately, some of our local pine species are under attack from a dangerous fungal pathogen.
Called pitch canker, this disease is threatening a number of pine species throughout the state, which means that homeowners and property managers must be vigilant and monitor their trees carefully.
We’ll try to help you do so below, by sharing the symptoms pitch canker causes, identifying the pines that are at greatest risk, and outlining the treatment options available.
What Is Pitch Canker?
Pitch canker is a fungal disease caused by Fusarium circinatum. Researchers currently suspect that it originated in Mexico (the global epicenter of pine species diversity) but was first documented in the United States in 1946. For a while, it was primarily limited to the Southeastern states, but by 1986, it had been discovered in California.
The fungus attacks a variety of pines (Pinus spp.), causing resin-leaking bark cankers to form on branches, twigs, and stems. If the bark in these areas is removed, the wood will appear stained and soaked in resin. In some cases, the cankers caused by this disease can completely encircle the affected area, effectively girdling the branch (or the entire tree, when it occurs on a main stem).
Pitch canker spreads in a variety of ways. The tiny fungal spores may travel on wind or water, and they may be carried from one location to the next via insects. Cut firewood is also known to be an important method by which the disease spreads.
Notably, the disease does not move within the tree. This means that if you see a tree with multiple cankers, they’ve each been caused by a separate colonization event.
Other Trees at Risk
Pitch canker primarily affects pines, but it can also infect Douglas-firs (Pseudotsuga menziesii), though it doesn’t typically cause symptoms; it’s often called a “stealth carrier.”
Symptoms of Pitch Canker
Pitch canker can cause pines to exhibit a number of different symptoms. A few of the most noteworthy include:
- Resin-Soaked Cankers: The most characteristic symptom is the presence of sunken or swollen cankers that ooze large amounts of pitch (resin) from infected branches, stems, or the trunk.
- Flagging Branch Tips: Infected shoots and branches often turn yellow, tan, or reddish-brown while the rest of the tree remains green, creating “flags” of dead foliage scattered throughout the canopy.
- Shoot Dieback: Pine pitch canker frequently kills new shoots and branch tips, leading to progressive dieback that can become more extensive with repeated infections.
- Dead Branches: As the disease progresses, individual branches may die completely, particularly in the lower and interior portions of the crown.
- Deformed Growth: New shoots that survive infection may become twisted, stunted, or otherwise misshapen, affecting the tree’s overall appearance and structure.
- Cone and Seed Damage: The fungus can infect cones, causing them to become resin-soaked, appear discolored, or fail to develop normally.
- Progressive Decline: Severely affected trees may exhibit a gradual loss of vigor over several years, eventually resulting in substantial canopy loss or, in highly susceptible species, tree mortality.
Species Susceptibility: Which Trees Are at Risk?
Pine pitch canker affects a number of pine species found throughout California. However, their susceptibility to the disease varies. Some may experience significant decline or mortality when infected; others are relatively resistant and typically suffer only minor symptoms.
Understanding which trees are most at risk can help homeowners and property managers make informed decisions when it comes time to plant new pine trees.
Highly susceptible species include:
- Monterey Pine (Pinus radiata): The species most severely affected by pine pitch canker in California and one of the most likely to experience significant canopy decline or mortality.
- Torrey Pine (Pinus torreyana): Although some populations have shown a degree of genetic variation in resistance, pitch canker is a serious threat to Torrey pines.
- Bishop Pine (Pinus muricata): Bishop pine is highly susceptible to infection and often develops extensive branch dieback that leads to a general decline in health.
- Knobcone Pine (Pinus attenuata): The knobcone pine is highly susceptible to pine pitch canker and may suffer significant branch dieback and decline.
Moderately susceptible species include:
- Ponderosa Pine (Pinus ponderosa): This species can become infected, but it is generally less severely affected than Monterey pine and often tolerates the disease relatively well.
- Sugar Pine (Pinus lambertiana): Sugar pines may develop infections, but they’re generally less susceptible than California’s most vulnerable pine species.
- Coulter Pine (Pinus coulteri): Coulter pine is susceptible to infection in some cases, but it is not typically one of the most severely impacted species.
Relatively resistant species include:
- Canary Island Pine (Pinus canariensis): The Canary Island pine often remains healthy even when growing in areas where pine pitch canker is present.
- Italian Stone Pine (Pinus pinea): Commonly planted in California landscapes, the Italian stone pine is generally regarded as a relatively resistant species.
Pitch Canker Treatments
Unfortunately, there is no cure for pine pitch canker once a tree becomes infected. There are no fungicides or injections that have been shown to reliably eliminate the fungus from infected trees.
However, many infected trees can be successfully managed for years with appropriate care and monitoring. In fact, there are a few management strategies that can help slow the progression of the disease, reduce the tree’s stress, and help infected trees remain healthy for as long as possible.
A few of the most common management strategies include:
- Professional Pruning: Properly pruning infected branches can help remove active infection sites and improve the tree’s appearance.
- Supportive Care: Maintaining overall tree vigor through appropriate irrigation, mulching, and soil management can improve a tree’s ability to tolerate infections.
- Reducing Stress: Simply avoiding soil compaction, root damage, and improper pruning practices can help minimize stress that makes trees more vulnerable to decline.
- Insect Management: Because several insects can transmit the fungus, minimizing insect damage and maintaining tree health may help reduce opportunities for infection.
- Tree Removal: In cases of severe canopy loss, extensive dieback, or significant structural decline, removal may be the most appropriate long-term management option.
Although a pitch canker diagnosis can be concerning, many infected trees can survive for years with proper care and monitoring. However, early intervention and professional risk assessments are crucial for preserving valuable landscape trees and managing the potential hazards infected trees present.
Concerned About Pine Pitch Canker? We’re Here to Help.
If you’ve noticed resin-covered cankers, dying branches, or thinning foliage on one of your pines, don’t wait for the problem to worsen. Early diagnosis can make all the difference when it comes to preserving valuable trees and making informed management decisions.
The ISA-certified arborists at Adney Tree Service can identify pine pitch canker, assess the potential risk your tree presents, and recommend an appropriate course of action.
Contact us today to schedule an evaluation and keep your trees healthy, safe, and thriving.
Sources and References
- UC IPM – “Pitch Canker”
Peer-reviewed Pest Notes on pitch canker (Fusarium circinatum) covering host range, honey-colored lesions and crown dieback, spread, and management for California pines.
https://ipm.ucanr.edu/home-and-landscape/pitch-canker/ - Phytopathology – “Pitch Canker Disease of Pines”
Peer-reviewed review by T.R. Gordon synthesizing the biology, epidemiology, and host resistance of the pitch canker pathogen across its global range.
https://pubmed.ncbi.nlm.nih.gov/18943185/ - Arboriculture & Urban Forestry (ISA) – “Treatment of Pitch Canker on Monterey Pine With Fungisol Injection”
Peer-reviewed field study finding that fungicide trunk injection failed to eradicate or prevent pitch canker infections in mature Monterey pines.
https://auf.isa-arbor.com/content/14/5/135 - Forest Pathology – “Pitch Canker of Pine Trees”
Educational reference by forest pathologist Jim Worrall detailing the disease’s hosts, symptoms, disease cycle, and worldwide movement.
https://forestpathology.org/canker/pitch/ - San Francisco Public Works – “Pine Pitch Canker Recommendations”
Municipal urban-forestry guidance on managing pitch canker in city pines, including planting, pruning sanitation, and species-selection recommendations.
https://sfpublicworks.org/services/pine-pitch-canker-recommendations - Torrey Pines Conservancy – “Pitch Canker: Protecting the Rare and Resilient Torrey Pines”
Conservation update on efforts by California State Parks, San Diego Zoo Wildlife Alliance, and the Pitch Canker Task Force to protect Torrey pines in the reserve.
https://www.torreypines.org/protecting-the-rare-and-resilient-torrey-pines-amid-pitch-canker-challenges/
