With its rugged, wind-sculpted silhouette, the Monterey cypress (Hesperocyparis macrocarpa) is a familiar sight along the Central and Northern California coast.
Drive along Highway 1 near Half Moon Bay, walk beneath the trees of San Francisco’s Presidio, or visit a coastal property from Aptos to Marin, and there’s a good chance you’ll spot several. And that’s actually pretty noteworthy, given the fact that the Monterey cypress isn’t technically native to the Bay Area.
The species was first introduced to our region back in the late 1800s, when the U.S. Army planted more than 19,000 of them at the Presidio in an effort to help shelter the windswept military post.
However, a serious disease known as cypress canker has been threatening them for nearly as long and continues to put Monterey cypresses across the Bay Area at risk.
Caused by the fungus Seiridium cardinale, cypress canker can kill individual branches, spread throughout the canopy, and eventually threaten the entire tree.
We’ll explain how cypress canker spreads, why Monterey cypress is so vulnerable, the signs to watch for, and what you can do to protect a healthy tree or manage one that’s already infected.
What Is Cypress Canker?
Cypress canker is a fungal disease that affects trees in the cypress family, with Monterey cypress being particularly vulnerable to severe damage.
The fungus enters through wounds or damaged bark and develops in the living tissue beneath.
As the cankers expand, they interfere with the movement of water through affected branches. Foliage beyond the infection begins to brown and die, sometimes leaving conspicuous patches of dead branches scattered through an otherwise green canopy.
Over time, individual cankers may expand or merge, killing increasingly large branches. If the disease reaches the main trunk, the damage can eventually threaten the entire tree.
Cypress Canker’s Bay Area Origins
Cypress canker may now be found around the world, but its documented history starts remarkably close to home.
Cypress canker was first identified on Monterey cypress trees in Palo Alto and described by plant pathologist W.W. Wagener in 1928. But notes from botanist Willis Jepson suggest the disease may have been present there as early as 1885.
From that Peninsula starting point, cypress canker spread throughout the region, with early reports coming from Alameda, Santa Clara, and San Mateo counties. The initial epidemic was devastating, killing more than 30,000 Monterey cypresses and Italian cypresses (Cupressus sempervirens).
California launched eradication efforts in the late 1930s, but by then the disease had become established across much of the state.
The story eventually reached far beyond California. Genetic research published in 2011 identified California as the most likely source of the cypress canker epidemic that devastated Mediterranean cypress populations.
Today, S. cardinale is found around the world, giving this Bay Area tree disease a remarkable international history.
How Cypress Canker Spreads
Cypress canker spreads primarily through water, with rain splash and wind-driven rain carrying fungal spores from infected cankers to susceptible trees. The fungus can also move on contaminated pruning tools or infected plant material, including nursery stock.
Insects may play a role, too. Some cypress bark beetles and other insects have been associated with the movement of S. cardinale spores, although this appears to be a secondary route of spread rather than the primary one.
However the spores arrive, the fungus needs an opening to infect the tree. Natural wounds, pruning cuts, storm damage, and tissue injured by insects can all provide entry points.
Weather can also influence infection. Prolonged periods of fog or light rain combined with moderate temperatures create favorable conditions for the disease to develop.
Monterey Cypress Is Especially Vulnerable to Cypress Canker
Not all cypress trees face the same risk from cypress canker. Monterey cypress is one of the species most vulnerable to severe disease, particularly when planted in suboptimal locations.
Monterey cypress has an extremely limited native range along California’s Central Coast, where it evolved under cool, maritime conditions. Trees planted farther inland may experience very different growing conditions and can be especially susceptible to cypress canker.
Drought stress can compound the problem. Cankers tend to enlarge faster on water-stressed trees, potentially increasing the amount of damage an infection causes.
However, other cypress trees found throughout the Bay Area can develop the disease, too, including:
- Italian cypress (Cupressus sempervirens): This tall, narrow Mediterranean species is widely planted in California landscapes and can develop cypress canker.
- Leyland cypress (× Hesperotropsis leylandii): This fast-growing Monterey cypress hybrid is commonly planted for screening and is also susceptible to the disease.
Signs and Symptoms of Cypress Canker
Cypress canker can be difficult to spot when infections are small or developing high in the canopy. Knowing what the disease looks like can help you recognize a potential problem before it becomes more extensive.
Some of the most recognizable signs of cypress canker include:
- Isolated Branch Dieback: Foliage on an infected branch may first turn yellow, then brown as the canker expands and interferes with water movement.
- Resinous Cankers: Infected branches or trunks may develop sunken or flattened areas of diseased bark that ooze sticky resin.
- Discolored Bark: Canker margins may appear darker than surrounding bark, while the tissue beneath infected bark can develop a reddish-brown discoloration.
- Scattered Brown Foliage: Individual branches or sections of the canopy may brown while surrounding foliage remains green, creating an uneven pattern of dieback.
- Expanding Cankers: As cankers enlarge, they can girdle branches and kill the foliage beyond the infected area. In severe cases, cankers may also develop on the trunk.
Cypress cankers may also attract cypress bark moths, but these insects are secondary invaders rather than the cause of the branch dieback.
These symptoms aren’t unique to cypress canker. Drought stress, insect damage, root problems, and other diseases can also cause browning or dieback, so an arborist should evaluate the tree before treatment decisions are made.
Can a Monterey Cypress Recover from Cypress Canker?
When cypress canker is limited to individual branches, careful pruning and ongoing tree care may help preserve healthy portions of the canopy, leave your arborist with more options, and prolong the tree’s life.
The outlook becomes less favorable when the disease is widespread or cankers develop on the main trunk. At that point, pruning may no longer be enough to manage the problem, and removal may need to be considered.
Cypress Canker Treatment and Management
There is no cure for an established cypress canker infection, so management focuses on removing infected tissue when possible and determining how much of the tree can reasonably be preserved. The appropriate approach depends on where the cankers are located and how much of the tree is affected.
Depending on the extent of the disease, management may include:
- Prune Infected Branches: When cankers are confined to individual branches, infected limbs can be removed by cutting into healthy wood below the affected area. When practical, pruning cuts should be made 1 to 2 feet below visible cankers.
- Disinfect Pruning Tools: Because S. cardinale can spread on contaminated tools, pruning equipment should be disinfected after working on infected trees and before it is used on healthy trees.
- Evaluate Severely Affected Trees: When cankers affect the main trunk or disease has caused extensive dieback, pruning may no longer be an effective management option. An arborist can evaluate the damage and determine whether continued management or tree removal is appropriate.
Reducing the Risk of Cypress Canker
You can’t eliminate every opportunity for cypress canker infection. But thoughtful planting and tree care can help reduce some of the conditions that make Monterey cypress more vulnerable.
A few ways to support and protect your trees include:
- Prune in Dry Conditions: When pruning is necessary, choose dry conditions and avoid unnecessary wounds that can provide entry points for the fungus.
- Choose Planting Sites Carefully: Monterey cypress is best suited to areas under the direct influence of California’s cool coastal climate. For inland properties, an arborist can recommend species better suited to local growing conditions.
- Prevent Drought Stress: Provide appropriate irrigation during extended dry periods, particularly for trees experiencing water stress. Avoid overwatering or allowing the root zone to remain continually wet.
- Watch for Early Signs: Periodically check Monterey cypress trees for isolated brown branches, resinous cankers, or other changes in the canopy. If something looks unusual, have an arborist evaluate it before extensive dieback develops.
Cypress Canker in the Bay Area: FAQ
If you’re concerned about cypress canker on your property, these common questions can help you understand what the disease means for your trees.
Is cypress canker contagious to other tree species?
Cypress canker primarily affects cypress trees and other members of the cypress family. Monterey cypress is particularly vulnerable, but Italian cypress, Leyland cypress, and several other related species can also develop the disease.
Can I prevent cypress canker just by watering my tree more?
No. Appropriate irrigation can help prevent drought stress, and cankers tend to enlarge faster on drought-stressed trees. But watering can’t prevent the fungus from entering through wounds or damaged tissue.
How fast does cypress canker kill a tree?
There isn’t a single timeline. Disease progression depends on factors such as tree condition, environmental conditions, and the location and extent of the cankers.
Are Monterey cypress trees native to the Bay Area?
Not exactly. Monterey cypress is native to California, but its natural range is remarkably small and limited to a few populations along the Central Coast. The species has been planted far beyond that native range, which is why Monterey cypress trees are now a familiar part of landscapes throughout the Bay Area.
Is there a fungicide for cypress canker?
There is no fungicide that cures an established cypress canker infection. Management instead focuses on pruning infected branches when practical and evaluating how much of the tree is affected.
Should I remove a Monterey cypress with cypress canker?
Not necessarily. When infection is confined to branches that can be safely pruned, management may help prolong the tree’s life. When disease is extensive or the main trunk is affected, an arborist can evaluate whether continued management is practical or removal should be considered.
How do I know if my tree has cypress canker or just storm damage?
Cypress canker can produce sunken or flattened lesions, resin oozing from infected areas, and yellow or brown foliage beyond a canker. Because storm damage and other tree-health problems can also cause branch dieback, an arborist can inspect the tree and determine what’s responsible.
Protect Your Bay Area Cypress Trees
Not every Monterey cypress showing branch dieback is destined for removal. When cypress canker is limited to individual branches, pruning infected tissue and reducing tree stress may help preserve healthy portions of the canopy and prolong the tree’s life.
The Adney Tree Service team has years of experience caring for the cypress, pine, and oak trees that define Santa Cruz County and the greater Bay Area. If your Monterey cypress is showing signs of canker or unexplained decline, schedule an assessment with an ISA-certified arborist to find out what your tree needs.
Contact Adney Tree Service today to get the expert guidance you need to protect your Monterey cypress and the landscape around it.
Sources & References
- University of California Integrated Pest Management – “Cypress Canker” – California-specific guidance on cypress canker symptoms, transmission, host susceptibility, environmental conditions, and management. Supports the discussion of Monterey cypress susceptibility away from direct coastal influence; infection through wounds and damaged tissue; spread by rain, contaminated pruning tools, and infected nursery stock; faster canker enlargement on drought-stressed trees; and pruning infected branches as a management strategy.
https://ipm.ucanr.edu/home-and-landscape/cypress-canker/ - California Department of Food and Agriculture – “California Pest Rating Profile for Seiridium cardinale” – California-specific history and risk assessment documenting the first identification of cypress canker on Monterey cypress in Palo Alto, evidence suggesting its presence there as early as 1885, the early epidemic that killed more than 30,000 Monterey and common cypress trees, and attempted eradication efforts during the 1930s. Also provides information on host range, symptoms, transmission, and disease distribution in California.
https://blogs.cdfa.ca.gov/Section3162/wp-content/uploads/2024/08/Seiridium-cardinale.pdf - Danti, R., and Della Rocca, G. – “Epidemiological History of Cypress Canker Disease in Source and Invasion Sites,” Forests (2017) – Peer-reviewed research tracing the history and epidemiology of Seiridium cardinale in California and abroad. Supports the Palo Alto origin of the documented disease history, early reports in Alameda, Santa Clara, and San Mateo counties, losses of more than 30,000 cypress trees, severe damage to inland Monterey cypress plantings, and differences observed between inland plantings and trees in the species’ native coastal range.
https://doi.org/10.3390/f8040121 - Della Rocca, G., et al. – “Sequence and Simple-Sequence Repeat Analyses of the Fungal Pathogen Seiridium cardinale Indicate California Is the Most Likely Source of the Cypress Canker Epidemic for the Mediterranean Region,” Phytopathology (2011) – Peer-reviewed population-genetics research identifying California as the most likely source of the S. cardinale population responsible for the Mediterranean cypress canker epidemic. Supports the article’s discussion of California’s role in the disease’s later international spread without implying that the pathogen itself was proven to originate specifically in Palo Alto.
https://pubmed.ncbi.nlm.nih.gov/21879790/ - Pacific Northwest Plant Disease Management Handbook – “Cypress (Cupressus spp.)—Canker” – Extension guidance on cypress canker disease biology, symptoms, transmission, and cultural management. Supports descriptions of yellowing and browning foliage, resinous and sunken cankers, branch dieback, infection through natural or insect-damaged wounds, rain-splashed spores, increased canker growth on drought-stressed trees, pruning infected branches into healthy tissue, and pruning-tool sanitation.
https://pnwhandbooks.org/plantdisease/host-disease/cypress-cupressus-spp-canker - Aylward, J., et al. – “High Genetic Diversity of the Cypress Canker Pathogen Seiridium cardinale in the Southern Hemisphere,” Plant Pathology (2026) – Recent peer-reviewed research on the genetics and global movement of S. cardinale. Supports California as the pathogen’s presumed native range, water-mediated local dispersal, occasional insect-assisted dispersal including cypress bark beetles, and the importance of human movement of infected plant material in the pathogen’s global distribution.
https://bsppjournals.onlinelibrary.wiley.com/doi/10.1111/ppa.70212 - National Park Service – “Planting with a Purpose: Eucalyptus and the U.S. Army” – Historical background for the article’s opening, documenting the U.S. Army’s planting of more than 19,000 Monterey cypress trees at the Presidio and the use of forest plantings for wind protection and other practical purposes around roads, residences, and military buildings.
https://www.nps.gov/goga/blogs/planting-with-a-purpose-eucalyptus-and-the-u-s-army.htm
