Cercospora Leaf Spot

Cercospora leaf spot is a fungal disease commonly affecting hydrangeas and crape myrtles. It is most prevalent from July to October and is one of the most frequently observed diseases on hydrangeas.

What Causes Cercospora Leaf Spot?

🌧 Midsummer weather conditions—especially humidity and warm temperatures—create an ideal environment for fungal activity.

💦 Rainfall and overhead irrigation contribute to the spread of spores, intensifying the infection.

🌦 Late summer rain increases the risk of defoliation and plant decline.

Will Cercospora Kill My Plants?

❌ No, but it can weaken the plant. Cercospora is primarily an aesthetic issue. Repeated severe infections can reduce plant vigor over time due to defoliation.

Symptoms on Hydrangea

🔍 Early Symptoms:

• Small, purple, circular spots appear on the leaves.

• Spots begin as tiny lesions but gradually enlarge. 

⚠️ Advanced Symptoms:

• Spots become irregular or angular in shape.

• Centers turn tan or gray with a purple or brown border.

• Severe infections can cause leaves to turn yellow-green and drop prematurely.

Symptoms on Crape Myrtle

🔍 Early Symptoms:

• Circular or irregular brown spots about ¼ inch in diameter.

• Leaves that appear twisted or distorted.

• Leaves turning yellow, orange, or red.

• Premature leaf drop from the tree.

Management

✅ Watering Practices

• Avoid irrigation directly onto the foliage. Overhead watering splashes and spreads the fungus.

  • Use drip irrigation or a soaker hose when possible.

• Water in the morning to allow for quick drying of excess moisture. 

✅ Leaf Cleanup & Removal

• Collect and dispose of fallen leaves before new spring growth emerges to reduce overwintering fungal spores.

✅ Ensure good air circulation

• Avoid overcrowding to improve airflow and minimize humidity buildup.