Sonoma County Fruit Tree Disease Management

Protect your orchard from lasting damage

A glorious Mediterranean climate is at the heart of why Sonoma is such a wonderful place for people and fruit trees, but our unique weather also creates an environment in which common plant diseases thrive. Our mild winters don’t get quite cold enough to kill off pathogens, and our rainfall with high humidity are a boon to fire blight, especially when spring temperatures climb above 65°F during bloom periods. Sonoma Valley’s droughts cause our fruit trees to be stressed, making them more susceptible to bacterial and fungal infections of all kinds, as well as pest infestations. The varied soils here also contribute to pathogen development—areas with more clay retain moisture, and heavy rains (or improper irrigation) create saturated, oxygen-free soil, which soon produces root rot like Phytophthora.
Fortunately, many of these issues can be managed or even avoided altogether with proper fruit tree maintenance. Knowing what to look for, catching symptoms early, and applying the right care go a long way toward keeping your orchard healthy and productive.

Branch of healthy, ripening fruit in a well-maintained Sonoma orchard, showing the impact of consistent care and disease prevention.

How We Help–Natural Plant Disease Control

Sonoma Pruner takes a holistic approach to fruit tree disease prevention and management. Owner Madaline Duran’s years of experience and innate ability to read a tree enables her to identify initial plant disease symptoms and take steps to address them.

Madaline Duran carefully pruning a fruit tree branch—part of her hands-on approach to managing plant diseases in Sonoma orchards.

Diagnosis

We’ll look for signs of problems, including pear blight, apple tree scab, powdery mildew, and root rot.

Sanitation

Just like in humans, fruit tree illnesses are communicable. To help avert expansion throughout your orchard, we’ll clear out infected branches and leaves as well as disinfect tools while working to arrest bacterial pathogen spread.

Organic Remedies and Preventative Practices

The cause of fruit tree disease is generally the result of a combination of things, including weather, tree health, and soil. Similarly, there isn’t a single solution to reviving your fruit trees for good. Therefore, our suggested care plan will include solutions such as fruit tree pruning in addition to organic plant disease treatments.

  • Smart watering: Whether due to heavy, sustained rains, improper irrigation, or good intentions, saturated soil can cause all manner of problems.
  • Airflow-focused pruning: This helps lower the chance of fungal growth by reducing excess moisture.
  • Organic treatments: Neem oil for trees, copper sprays, and other natural remedies work well for common fruit tree diseases. These are applied preventatively during dormant season and bloom periods when trees are most vulnerable.
  • Soil and nutrient support: Healthy soil and proper tree feeding help to make your orchard more pathogen-resistant.
  • Resistant varieties: When planting fruit trees, we recommend varieties and rootstocks that are naturally resistant to common Sonoma diseases like fire blight and root rot.

Pear Blight: What to Know and How to Treat It

What is generally called “fire blight” we call “pear blight” here in Sonoma. This bacterium has devastated entire pear orchards, with some years seeing widespread tree loss across the North Bay.

Fire blight is caused by the bacterium Erwinia amylovora. It affects both apples and pears, but pears are often more severely affected. Call the disease what you will, but it is one of the most common and damaging in Sonoma’s home orchards.

The time to be most vigilant is in the spring, when we’re getting rain and temperatures are above 65°F. That combination creates the perfect infection conditions for pear blight. It usually strikes the ends of pear, apple, and quince branches, turning leaves and shoots brown or black while the rest of the tree may still appear healthy.

How to Treat Fire Blight

  • Act fast: Check trees daily during spring—even one extra day means cutting more branches.
  • How it proliferates: Wind and insects carry the bacteria, so expect annual recurrence once infected.
  • Before starting, mix a sterilizing solution of 10% bleach and 90% water in a spray bottle and have a large plastic bag ready.
  • Using clean pruners, cut 6–12 inches below the visible signs of blight.
  • Discard all cuttings and any fallen leaves directly into the bag—don’t compost them.
  • Sterilize your pruners after each cut.
  • When finished, seal the bag and throw it away in the trash—it is not green waste.
  • Nip future outbreaks in the bud by feeding regularly, ensuring water drains well, keeping irrigation 18″ from the trunk, and never spraying water directly on the trunk.

Catching pear blight early is key—even a single day can make the difference between a small cleanup and major loss.

Close-up of a ripening pear on a tree, surrounded by green leaves—highlighting fruit tree care and disease prevention in Sonoma.

Common Plant Diseases in Sonoma Orchards

Apple Scab

This fungal disease causes olive-colored spots on fruit and foliage. Some apple varieties are more vulnerable than others. To minimize its spread, remove debris, and prune for airflow.

Powdery Mildew

Unlike most fungal infections, this mildew thrives in dry conditions with poor airflow. Powdery mildew on fruit trees appears as a white, dusty layer on leaves, stems, and fruit. Proper pruning and planting resistant varieties help to keep it at bay.

X-Disease

In 1931, this devastating phytoplasma disease destroyed Sonoma County’s sweet cherry industry. Today, it still affects stone fruits including cherries, peaches, plums, and nectarines, causing trees to produce small, pale, tasteless fruit and yellowed, curled leaves. Sap-sucking insects called leafhoppers spread the disease, and infected trees gradually decline and eventually die. Since there’s no cure, it’s critical to detect x-disease early and immediately remove compromised trees.

Rust

When you see orange or rust-colored spots, especially on the undersides of leaves, you know you’ve got rust. To treat rust on trees, remove affected foliage and use organic fungicides when needed.

Root Rot

Root rot is a soil-borne disease made worse by poor drainage or overwatering. Root rot symptoms include yellowing, slow growth, and general decline. You can address it through better soil and irrigation adjustments.

Brown Rot

This fungus attacks stone fruits, causing rapid fruit decay with tan-gray fuzzy growth. It advances quickly in warm, humid conditions and can destroy entire crops. Remove infected fruit immediately and apply preventatives.

Ready to grow?

Schedule your consultation

Fruit Tree Disease FAQ

What tree fungus treatments do you recommend?
The key to effective, long-lasting results is to combine strategies, thus, we recommend a comprehensive approach that goes beyond just spraying. Our tree fungus treatment includes organic remedies like copper sprays and neem oil for plant disease control, plus proper sanitation, airflow-focused pruning, informed watering practices, and soil and nutrient support.
How do you prune fruit trees to prevent disease?
The focus here is to shed light on areas where humidity and moisture collect and disease thrives. So, in this case, we prune overcrowded branches and any diseased wood, sterilizing tools all the while to hinder transmission.
Do you offer plant pathology services?
Yes, we identify the specific pathogens affecting your orchard and create customized management plans.
Is neem oil effective for fruit tree diseases?
Neem works well as part of an integrated approach, especially for fungal issues like powdery mildew.