Summer in California’s Coastal Peninsula and South Bay Area may look bright and green, but beneath the canopy, fungal pathogens are hard at work. If you have coast live oaks, bay laurels, or redwoods on your property, now’s the time to inspect them closely—because what you can’t see could be harming your trees. 

What Fungal Threats Are Active Right Now? 

While your trees soak up the summer sun, hidden fungal diseases can quietly take hold. Here are the top culprits we’re seeing in our region this season: 

Anthracnose 

A common leaf disease, anthracnose, causes brown or black blotches and premature leaf drop. It favors warm, wet conditions—like those caused by morning fog or coastal humidity. 

Powdery Mildew 

Look for white, powdery coatings on leaves of Japanese maples, redwoods, and other ornamentals. While not always fatal, repeated infections can stress trees and stunt growth. 

Phytophthora Species 

This water mold includes multiple aggressive pathogens, most notably Phytophthora ramorum, the cause of Sudden Oak Death (SOD). It attacks roots, trunks, and foliage, often progressing without visible symptoms until it’s too late. 

Spotlight on Sudden Oak Death (SOD) 

Sudden Oak Death is the single most concerning fungal threat to our local oak woodlands. It spreads easily, often jumping from infected California bay laurels to nearby coast live oaks and tanoaks. 

How It Spreads 

Spores travel via rain splash, wind-driven mist, and contaminated tools or footwear. Bay laurels are especially dangerous as they often show minor symptoms but harbor high spore loads. 

Trees at Risk 

• Coast live oak 
• Tanoak 
• California bay laurel (acts as a carrier) 

Symptoms to Watch For 

• Leaf spotting and browning, especially on bay laurel 
• Bleeding cankers on oak trunks 
• Twig and branch dieback 
• Rapid decline or sudden death of large oaks 

How to Identify the Warning Signs 

Early detection is your best defense. 

Symptoms to Watch 

• Wilting or curling leaves 
• Sunken bark or oozing sap (cankers) 
• Dieback at branch tips 
• Discoloration or spotting inconsistent with seasonal changes 

Don’t Confuse With: 

• Drought stress (leaves are usually crispy or bronzed uniformly) 
• Insect damage (chewed or skeletonized leaves, visible pests) 

If you’re unsure, it’s time to call in a certified arborist. Accurate diagnosis is essential to avoid unnecessary removals or missed treatment windows. 

Containment and Next Steps 

Once fungal pathogens take hold, they don’t go away on their own. 

Why Early Detection Matters 

Treatments are most effective when caught early—especially with SOD. Delay can mean irreversible damage or loss of mature trees. 

Best Practices 

• Prune infected areas carefully and sanitize tools after each cut 
• Dispose of debris offsite—never compost infected leaves or wood 
• Manage or remove nearby bay laurels if they pose a high-risk source 
• Apply plant health treatments (like bio-hydration or deep root fertilization) to boost tree immunity 

Expert Insight 

“What we’re seeing this season across San Mateo, Woodside, and the foothills is a noticeable uptick in Sudden Oak Death activity—especially following early summer fog and high humidity. Bay laurels are showing strong spore presence, which means nearby oaks are at elevated risk.”
— Maguire Tree Care Certified Arborist 

Frequently Asked Questions 

Q: How fast can Sudden Oak Death kill a tree?
A: In coast live oaks, SOD can cause death within a few months once bleeding cankers appear, especially in drought-stressed trees. 

Q: Can it spread from my neighbor’s bay laurel to my oak?
A: Yes. Spores can travel up to hundreds of feet under the right conditions. Proximity to infected bay laurels is a major risk factor. 

Q: Should I remove infected trees or treat them?
A: It depends. Some trees may be treated or monitored, but severely infected or high-risk trees might need removal to protect surrounding trees. 

Q: Is it safe to compost infected leaves or branches?
A: No. Infected material should be bagged and removed from your property to prevent further spread. 

Q: Can drought make fungal infections worse?
A: Absolutely. Stressed trees are more susceptible to infection and less capable of recovery. 

Contact Maguire Tree Care for Pest and Disease Treatment 

Worried about oak decline or fungal infections? Don’t wait until it’s too late. 

📞 Call Maguire Tree Care at 650-719-2253 for an expert evaluation, or schedule your consultation online. 

Let’s protect your trees—and our local forest heritage—together.