Protecting Sonoma & Napa Trees Before Dormancy

As fall settles into Sonoma and Napa counties, cooler nights and seasonal rains bring much-needed relief to drought-stressed landscapes. Unfortunately, this same weather also creates the perfect breeding ground for fungal tree diseases.

For homeowners, HOAs, and property managers, fall is the most important window to get ahead of threats like anthracnose, sudden oak death, and powdery mildew. Acting now helps protect your oaks, sycamores, and ornamentals before they enter dormancy—and prevents costly damage that often shows up during winter storms.

Why Fall Is a High-Risk Season for Fungal Diseases

While summer heat tends to slow disease spread, autumn moisture does the opposite. Rain, coastal fog, and cooler air create the exact conditions fungi need to thrive.

• Anthracnose spores wash down from infected leaves and twigs, spreading through wet canopies.
• Powdery mildew flourishes in mild, damp weather, leaving trees coated in its telltale white residue.
• Sudden Oak Death (SOD), a particularly devastating pathogen, spreads fastest during wet fall months, attacking California’s signature oak species.

Here in wine country, with its mix of oak woodlands, vineyard-adjacent landscapes, and ornamental plantings, these fungal diseases can spread quickly if left unchecked.

Local Impact: Oaks, Sycamores, and Vineyard-Adjacent Trees

Sonoma and Napa’s landscapes are uniquely vulnerable:

• Oaks (particularly coast live oak and tanoak) face the constant threat of Sudden Oak Death, a disease that has already claimed millions of trees in California.
• Sycamores are highly susceptible to anthracnose, leading to leaf browning and premature leaf drop that weakens their canopies.
• Ornamentals like roses, crape myrtles, and maples often battle powdery mildew during the damp season, impacting both health and appearance.

The combination of coastal moisture and vineyard irrigation creates microclimates where fungi can thrive well into late fall.

Early Warning Signs to Watch For

Catching symptoms early makes treatment more effective. Keep an eye out for:

• Anthracnose: Browning or blotched leaf margins, curling, and premature defoliation.
• Powdery Mildew: White, powdery film on leaves, buds, or stems.
• Sudden Oak Death: Bleeding, reddish-brown cankers on oak trunks, along with canopy thinning and branch dieback.

If you see these signs on your property, don’t wait—fungal diseases spread quickly when untreated.

What Happens If You Ignore Tree Diseases

Many fungal infections may appear cosmetic at first, but the long-term consequences can be serious:

• Weakened canopies make trees more vulnerable to storm damage and branch failure.
• Chronic infections reduce energy reserves, stunting growth and reducing natural resilience.
• In the case of Sudden Oak Death, untreated infections often result in complete tree loss—and the removal of a mature oak is far more costly than preventative care.

Treatment Options for Fall

The good news? Our plant health care (PHC) programs can contain and manage fungal diseases before they cause lasting damage.

• Fungicide Injections & Sprays: Targeted treatments to control anthracnose, powdery mildew, and sudden oak death.
• Disease Monitoring: Regular PHC inspections to catch and manage outbreaks early.
• Deep Root Fertilization: Boosts tree resilience and helps them recover from disease stress.
• Soil Care Programs: Improving soil health increases natural defenses against fungal spread.

Timing Matters: Why Act Now

October and early November are the critical treatment window. Once trees enter full dormancy, their ability to respond to treatments drops significantly. By taking action now, you protect trees through the wettest months and set them up for a healthier spring.

Work With Sonoma & Napa’s Local Experts

At Image Tree Service, our certified arborists bring over two decades of experience caring for Northern California’s trees. We understand the unique fungal pressures that threaten our local landscapes—and we know how to contain them. Whether you manage a single backyard oak or an entire HOA landscape, our tailored PHC treatments keep your trees thriving safely.

Protect Your Trees Before Disease Spreads

Don’t let fungal diseases take hold this fall. Contact Image Tree Service today at (773) 718-5362 to schedule a plant health care treatment and keep your trees strong before winter dormancy.