Healthy vines are the foundation of exceptional wines. But even the best-managed vineyards in Sonoma County and beyond face the constant challenge of vineyard diseases. Left unchecked, these diseases can reduce yields, compromise grape quality, and even destroy entire blocks of vines.

At Clendenen Vineyard Management, we’ve spent more than three decades helping vineyard owners protect their vines from common threats. Below, we’ll explore the most prevalent vineyard diseases and share proven strategies to prevent them.

1. Powdery Mildew

What it is: Powdery mildew is one of the most common and damaging vineyard diseases worldwide. It appears as a white, powdery coating on leaves, shoots, and grape clusters, reducing photosynthesis and fruit quality.

Prevention:

• Maintain open canopies to improve airflow and reduce humidity.
• Apply fungicide sprays at critical growth stages.
• Monitor regularly during warm, dry conditions, when the disease thrives.

2. Downy Mildew

What it is: Unlike powdery mildew, downy mildew is caused by a water mold and appears as yellowish, oily spots on leaves with a white fuzz underneath. It spreads rapidly in wet, humid conditions.

Prevention:

• Use proper irrigation techniques to avoid excess leaf wetness.
• Prune for airflow to minimize humidity in the canopy.
• Apply preventative sprays when conditions favor outbreaks.

3. Botrytis (Gray Mold)

What it is: Botrytis cinerea, also known as “gray mold,” infects grapes close to harvest. While it can create the prized “noble rot” in dessert wines, uncontrolled infections devastate fruit quality.

Prevention:

• Thin clusters and leaves to reduce shading and moisture.
• Harvest promptly when grapes are ripe to avoid prolonged exposure.
• Monitor closely during wet weather near harvest.

4. Pierce’s Disease

What it is: Spread by the glassy-winged sharpshooter insect, this bacterial infection blocks water movement in vines. Symptoms include leaf scorch, fruit shrivel, and eventual vine death.

Prevention:

• Control sharpshooter populations through monitoring and barriers.
• Remove infected vines to limit spread.
• Plant tolerant or resistant varietals in high-risk areas.

5. Eutypa Dieback (Dead Arm Disease)

What it is: A fungal disease that enters through pruning wounds, causing stunted shoots, poor yields, and eventually vine death.

Prevention:

• Prune late in the season to reduce infection risk.
• Protect pruning cuts with fungicide or sealants.
• Remove and destroy infected wood promptly.

Protecting Vineyards for the Long Term

Vineyard diseases are a serious concern, but with careful monitoring, proactive prevention, and expert management, they don’t have to threaten your vineyard’s future.

At Clendenen Vineyard Management, we partner with vineyard owners across Sonoma County to implement disease prevention strategies rooted in decades of field experience. From canopy management to precise spray programs, our family-run team ensures your vines stay healthy and your grapes reach their full potential.

📞 Contact Clendenen Vineyard Management today to learn how we can protect your vineyard from disease and keep your vines flourishing year after year.