From wildfires to construction damage to increasingly lengthy droughts, trees in the Greater Bay Area face threats on all fronts. But while these kinds of environmental and cultural stressors are certainly important and lead to the death and decline of countless trees in our area, a variety of harmful invertebrates and microorganisms also place our trees at risk.
Fortunately, it’s easy for homeowners and property managers to get the expert support needed to help their trees remain healthy: Simply contact the Adney Tree Service team. We offer treatments and preventive tree care services that target a number of important pests and pathogens in the Bay Area.
Tree Diseases We Diagnose & Treat
Some of the tree diseases present in the Bay Area are relatively minor threats that only cause cosmetic damage. But others can kill even healthy trees. In either case, one of our ISA-certified arborists can help diagnose and treat the conditions listed below.
Sudden Oak Death
Sudden oak death (SOD) is one of the most serious tree diseases affecting California’s native oaks. Infected trees often develop bleeding trunk cankers, canopy thinning, and branch dieback, and may eventually die if the disease progresses.
- Commonly Affected Trees: Coast live oak, tanoak, and California black oak.
- Typical Treatments: Phosphonate treatments, sanitation practices, and supportive health strategies.
Pitch Canker
Pitch canker is a fungal disease that primarily affects pine trees, and it is especially problematic for Monterey pine. Symptoms often include resinous cankers, branch dieback, shoot mortality, and progressive canopy decline.
- Commonly Affected Trees: Monterey pine and related pine species.
- Typical Treatments: Selective pruning, sanitation, and practices that reduce environmental stress.
Fusarium Dieback
Fusarium dieback is commonly associated with invasive shothole borers and can affect a wide variety of landscape trees. Symptoms often include branch dieback, vascular discoloration, and canopy thinning that worsens over time.
- Commonly Affected Trees: Sycamore, box elder, coast live oak, and other landscape trees.
- Typical Treatments: Integrated management targeting both the pathogen and its insect vector.
Phytophthora Root Rot
Phytophthora root rot is a soilborne disease that damages root systems and limits a tree’s ability to absorb water and nutrients. Common symptoms include leaf yellowing, canopy thinning, poor vigor, and gradual decline.
- Commonly Affected Trees: Oaks, Douglas-firs, fruit trees, and other common Bay Area tree species.
- Typical Treatments: Improving drainage, adjusting irrigation practices, and phosphonate-based treatment programs when appropriate.
Foamy Bark Canker
Foamy bark canker is an emerging disease affecting coast live oaks in parts of California. Infected trees may develop bleeding lesions, foamy sap exudate, canopy decline, and branch dieback.
- Commonly Affected Trees: Coast live oak.
- Typical Treatments: Monitoring, sanitation, pruning, and management of bark beetle activity.
Cypress Canker
Cypress canker is a destructive disease that can cause extensive branch dieback and decline in susceptible conifers. Resin flow, cankers, and thinning canopies are among the most common symptoms.
- Commonly Affected Trees: Monterey cypress and related conifers.
- Typical Treatments: Pruning infected branches and reducing environmental stress.
Armillaria Root Rot
Armillaria root rot is a common root disease that attacks stressed and weakened trees. Symptoms often include canopy thinning, reduced vigor, root decay, and eventual structural failure or mortality.
- Commonly Affected Trees: Oaks, cedars, and numerous hardwood and ornamental species.
- Typical Treatments: Improving site conditions, reducing stress, and removing severely affected trees when necessary.
Diplodia Shoot Blight
Diplodia shoot blight is a fungal disease that primarily affects pines and can significantly reduce their appearance and vigor. Dead shoots, stunted new growth, branch dieback, and canopy thinning are common symptoms.
- Commonly Affected Trees: Monterey pine and other susceptible pines.
- Typical Treatments: Sanitation pruning, stress reduction, and preventive fungicide applications when warranted.
Anthracnose
Anthracnose refers to a group of fungal diseases that commonly affect shade trees throughout the Bay Area. Symptoms often include leaf spotting, blotching, premature defoliation, and twig dieback.
- Commonly Affected Trees: Sycamore, oak, maple, ash, and many other broadleaf trees.
- Typical Treatments: Sanitation, pruning, and fungicide applications for high-value trees.
Powdery Mildew
Powdery mildew is easily recognized by the white, powder-like growth it produces on leaves. While often more cosmetic than life-threatening, severe infections can reduce vigor and distort foliage.
- Commonly Affected Trees: Oaks, sycamores, ornamentals, and numerous landscape plants.
- Typical Treatments: Improving airflow, reducing humidity, and fungicide applications when necessary.
Huanglongbing (Citrus Greening)
Huanglongbing (HLB), also known as citrus greening disease, is one of the most serious threats facing citrus trees in California. The disease is spread by the Asian citrus psyllid and often causes yellow shoots, blotchy leaf mottling, misshapen fruit, premature fruit drop, and progressive decline.
- Commonly Affected Trees: Orange, lemon, lime, grapefruit, mandarin, and other citrus species.
- Typical Treatments: There is currently no cure for HLB. Management focuses on early detection and removing infected trees.
Fire Blight
Fire blight is a bacterial disease that can spread rapidly through susceptible hosts. Infected trees often exhibit blackened shoots and branches that appear scorched by fire, along with rapid dieback.
- Commonly Affected Trees: Pear, apple, crabapple, and other members of the rose family.
- Typical Treatments: Pruning infected tissue and implementing practices that reduce disease spread.
Verticillium Wilt
Verticillium wilt is a vascular disease that interferes with a tree’s ability to transport water. Symptoms commonly include wilting foliage, branch dieback, and progressive canopy decline.
- Commonly Affected Trees: Maple, redbud, smoke tree, and other landscape trees.
- Typical Treatments: Improving tree vigor and selectively pruning affected branches.
Botryosphaeria Canker
Botryosphaeria canker is commonly associated with drought stress and other environmental pressures. Infected trees often develop bark cankers, branch dieback, and progressive canopy thinning.
- Commonly Affected Trees: Oaks, eucalyptus, redwoods, and other stressed landscape trees.
- Typical Treatments: Pruning affected branches and reducing environmental stress.
Rust Diseases
Rust diseases are a group of fungal pathogens that commonly cause colorful leaf spots and premature defoliation. Rusts are often more cosmetic than life-threatening, but severe infections can cause trees to decline over time.
- Commonly Affected Trees: Hawthorn, ornamental pear, and numerous landscape plants.
- Typical Treatments: Sanitation, host management, and fungicide applications when warranted.
Tree Pests We Diagnose & Treat
A variety of insects, mites, and other invertebrates can affect trees throughout the Bay Area. While some cause little more than cosmetic damage, others can weaken trees, contribute to decline, or even lead to tree loss if left unmanaged. Some of the most common tree pests we diagnose and treat are discussed below.
Invasive Shothole Borers
Invasive shothole borers are small beetles that attack a wide variety of trees while introducing harmful fungi into the vascular system. Common symptoms include tiny beetle entry holes, branch dieback, staining around galleries, and progressive canopy decline.
- Commonly Affected Trees: Box elder, sycamore, coast live oak, and numerous landscape trees.
- Typical Treatments: Monitoring, sanitation, targeted insecticide applications, and integrated management of both the beetles and the fungi they introduce.
Bark Beetles
Bark beetles commonly attack stressed or weakened conifers and can quickly overwhelm susceptible trees. Symptoms often include pitch tubes, boring activity beneath the bark, canopy discoloration, and eventually, death.
- Commonly Affected Trees: Pines and other conifer species.
- Typical Treatments: Preventive treatments, stress reduction, sanitation, and removal of heavily infested trees when necessary.
Eucalyptus Longhorned Borer
Eucalyptus longhorned borers primarily target stressed eucalyptus trees. Infested trees often exhibit bark splitting, branch dieback, and thinning canopies, which can eventually cause significant canopy loss.
- Commonly Affected Trees: Eucalyptus species.
- Typical Treatments: Improving tree vigor, monitoring infestations, and removing severely affected limbs or trees.
Red Gum Lerp Psyllid
Red gum lerp psyllids are sap-feeding insects that can significantly affect eucalyptus health and appearance. Common symptoms include leaf discoloration, premature leaf drop, canopy thinning, and reduced vigor.
- Commonly Affected Trees: Red gum eucalyptus and related eucalyptus species.
- Typical Treatments: Systemic insecticide treatments, biological controls, and measures to improve tree health.
Eugenia Psyllid
Eugenia psyllids are common pests of hedges and ornamental plantings throughout California landscapes. Infestations typically cause distorted, curled foliage and reduced aesthetic appeal.
- Commonly Affected Trees: Eugenia and brush cherry.
- Typical Treatments: Monitoring populations and applying targeted insecticide treatments when warranted.
Peppertree Psyllid
Peppertree psyllids feed on California pepper trees and can cause noticeable foliage distortion. Symptoms commonly include leaf curling, leaf drop, and reduced vigor.
- Commonly Affected Trees: California pepper trees.
- Typical Treatments: Monitoring and targeted treatments when infestations become severe.
Western Bark Beetle
Western bark beetles can contribute to oak decline and are associated with the spread of foamy bark canker. Infested trees often show signs of insect boring activity, canopy decline, and a progressive loss of overall vigor.
- Commonly Affected Trees: Coast live oak and related oak species.
- Typical Treatments: Monitoring, sanitation, and maintaining overall tree health.
California Oakworm
California oakworms are native caterpillars that periodically cause significant defoliation of oak trees. Although dramatic in appearance, healthy trees often recover from isolated outbreaks.
- Commonly Affected Trees: California native oaks.
- Typical Treatments: Monitoring populations and treating severe infestations when necessary.
Oak Twig Girdler
Oak twig girdlers damage small branches and twigs as part of their reproductive cycle. Symptoms often include twig dieback, branch flagging, and premature twig drop.
- Commonly Affected Trees: Coast live oak and other oak species.
- Typical Treatments: Pruning affected branches and removing infested material.
Erineum Mites
Erineum mites are microscopic pests that cause unusual growths on leaf surfaces. They typically produce velvety patches or blister-like growths that are more cosmetic than harmful.
- Commonly Affected Trees: Coast live oak and interior live oak.
- Typical Treatments: Monitoring and treatment only when infestations become significant.
Spider Mites
Spider mites are common during hot, dry conditions and can rapidly build to damaging populations. Symptoms often include leaf stippling, bronzing, needle discoloration, and premature leaf or needle drop.
- Commonly Affected Trees: Conifers, ornamentals, and drought-stressed landscape trees.
- Typical Treatments: Horticultural oils, miticides, and practices that improve tree vigor.
Scale Insects
Scale insects feed by extracting sap from leaves, twigs, and branches, often weakening trees over time. Common symptoms include honeydew production, canopy thinning, branch decline, and reduced vigor.
- Commonly Affected Trees: Oaks, pines, bay laurels, eucalyptus, and ornamental trees.
- Typical Treatments: Horticultural oils, systemic insecticides, and treatments targeting crawler-stage insects.
Aphids
Aphids are among the most common tree pests found in residential landscapes. They often produce sticky honeydew that can lead to sooty mold growth and other secondary issues.
- Commonly Affected Trees: Numerous landscape trees and shrubs.
- Typical Treatments: Horticultural oils, insecticidal soaps, biological controls, and systemic treatments when necessary.
Cottony Cushion Scale
Cottony cushion scale is a distinctive sap-feeding insect that can significantly affect ornamental plants and citrus trees. Infestations often result in reduced vigor, branch decline, and sticky honeydew deposits.
- Commonly Affected Trees: Citrus and ornamental landscape plants.
- Typical Treatments: Biological controls, horticultural oils, and targeted insecticide applications.
Citrus Leafminer
Citrus leafminer larvae tunnel through young leaves, creating visible winding trails and distorted foliage. Heavy infestations can reduce the quality and vigor of new growth.
- Commonly Affected Trees: Citrus trees.
- Typical Treatments: Monitoring and targeted treatments designed to protect new growth.
Tent Caterpillars
Tent caterpillars build distinctive silk tents in branch crotches and feed on surrounding foliage. Significant infestations can cause noticeable defoliation and aesthetic damage.
- Commonly Affected Trees: Oaks, fruit trees, and ornamental landscape trees.
- Typical Treatments: Pruning tents, biological insecticides, and targeted insecticide applications.
Leaf Beetles
Several leaf beetle species feed on eucalyptus foliage and can reduce tree vigor during heavy infestations. Damage often appears as a chewing injury and partial defoliation.
- Commonly Affected Trees: Eucalyptus species.
- Typical Treatments: Monitoring populations and applying treatments when damage becomes significant.
Other Tree Health Problems We Diagnose & Treat
Some tree health problems are caused by things other than pests or diseases, but they still require attention. A few of the most common examples are discussed below.
Sooty Mold
Sooty mold is a black fungal growth that develops on honeydew produced by aphids, scale insects, and other sap-feeding pests. While it rarely harms trees directly, it can indicate a significant insect infestation and reduce the tree’s appearance.
- Commonly Affected Trees: Trees affected by aphids, scale insects, and other honeydew-producing pests.
- Typical Treatments: Managing the underlying insect infestation and improving overall tree health.
Bacterial Wetwood (Slime Flux)
Bacterial wetwood is a condition that causes dark, wet, and sometimes foul-smelling sap to ooze from cracks or wounds in a tree’s trunk. It is often associated with stress, injuries, or bacterial activity within the wood.
- Commonly Affected Trees: Oaks, elms, maples, and other hardwoods.
- Typical Treatments: Supportive tree care and management of contributing stress factors.
Gummosis
Gummosis refers to excessive sap or gum production from a tree’s bark and is often a symptom rather than a disease itself. It may be associated with cankers, injuries, insect activity, or environmental stress.
- Commonly Affected Trees: Stone fruit trees and some conifers.
- Typical Treatments: Identifying and addressing the underlying cause while improving tree vigor.
Crown Rot
Crown rot occurs when decay develops around the root collar and lower trunk of a tree. Affected trees often exhibit poor growth, canopy decline, and progressive deterioration over time.
- Commonly Affected Trees: Numerous tree and shrub species growing in poorly drained soils.
- Typical Treatments: Improving drainage, correcting irrigation issues, and managing contributing pathogens.
Tree Pests & Disease: FAQ
Because tree pests and diseases can be difficult for homeowners and property managers to identify, questions about these tree threats are pretty common. Below are some of the questions we hear most frequently.
How can I tell if my tree has a pest problem or a disease?
Many pests and diseases cause similar symptoms, including leaf discoloration, canopy thinning, branch dieback, and premature leaf drop. A professional inspection is often the best way to identify the underlying cause and determine whether treatment is warranted.
Can a tree recover from a pest infestation or disease?
In many cases, yes. Trees often have an impressive ability to recover when problems are identified early and appropriate treatments are implemented. The likelihood of recovery often depends on the specific pest or disease and the severity of the problem, as well as how quickly treatment begins.
What are the most serious tree diseases in the Bay Area?
Several diseases can significantly impact Bay Area trees, including sudden oak death, Phytophthora root rot, Fusarium dieback, and Armillaria root rot. Early detection is often critical for preserving affected trees and protecting nearby specimens.
Can pests spread from one tree to another?
Yes. Many insect pests and disease-causing organisms can spread between nearby trees. Some move naturally through the landscape, while others are transported by insects, root grafts, contaminated plant material, or human activity.
Can drought stress make trees more vulnerable to pests and diseases?
Absolutely. Drought-stressed trees are often less able to defend themselves against insects, fungal pathogens, and other threats. This is one reason proactive tree care is especially important during extended dry periods.
Why is only one tree in a row declining?
Differences in soil conditions, root damage, drainage, species susceptibility, irrigation, and past injuries can all cause one tree to decline while neighboring trees remain unaffected.
Why are my trees’ leaves turning yellow or falling early?
Premature leaf discoloration and leaf drop can result from many different causes, including pests, diseases, drought stress, poor drainage, nutrient deficiencies, and environmental factors. Because several problems produce similar symptoms, a professional diagnosis is often necessary.
Let Adney Tree Service Help Keep Your Trees Healthy
It can certainly be stressful to see your trees being attacked by pests or infected with diseases. But many of the pests and pathogens that threaten Bay Area trees can be treated. The important thing is that you get professional assistance quickly, as this will give your trees the best chance of a full recovery.
If you notice any signs or symptoms that suggest your trees may be in failing health, contact the Adney Tree Service team. We’ll be happy to arrange for an on-site evaluation and provide you with a free estimate for the recommended services.
Sources & References
- San Francisco Public Works – “Pine Pitch Canker Recommendations”
An official municipal guidance document outlining management strategies, pruning restrictions, and disposal protocols designed to minimize the spread of pine pitch canker within the city’s urban forest canopy.
https://sfpublicworks.org/services/pine-pitch-canker-recommendations - University of California Agriculture and Natural Resources – “Pitch Canker in California”
A comprehensive technical bulletin detailing the biology, host vulnerability (particularly Monterey pine), and geographic distribution of the fungal pathogen Fusarium circinatum across coastal California ecosystems.
https://ucanr.edu/sites/default/files/2016-10/250412.pdf - Crop Protection (ScienceDirect) – “Pine Pitch Canker: Economic Impacts and Management Options”
A peer-reviewed journal article providing a global perspective on the economic damages caused by pine pitch canker in commercial forestry and detailing integrated pest management approaches for disease suppression.
https://www.sciencedirect.com/science/article/abs/pii/S026121941930273X - University of California Statewide IPM Program – “Huanglongbing (Citrus Greening)”
An authoritative agricultural resource tracking the vector dynamics of the Asian citrus psyllid and detailing monitoring and regulatory protocols for managing the destructive, incurable bacterial disease Huanglongbing.
https://ipm.ucanr.edu/agriculture/citrus/huanglongbing/#gsc.tab=0
