Cercospora Leaf Spot on Crepe Myrtle

The yellow and brown spots on your 3-year-old crepe myrtle, without powdery residue or visible pests, match Cercospora leaf spot (Cercospora lythracearum), a fungal disease favored by warm, humid weather.

Symptoms

• Yellow to tan spots (1/8–1/4 inch) on upper leaf surface.
• Whitish-gray sporulation on lower surface (may need magnification).
• Spots merge, leaves yellow, and premature defoliation occurs in late summer.
• Susceptible cultivars lose most leaves by fall.

Management

1. Cultural: Full sun, proper spacing, avoid overhead irrigation, rake/destroy fallen leaves.
2. Fungicides (if severe): Apply at bud break and repeat per label.
   • Thiophanate-methyl (Ferti-lome Halt, Green Light Systemic)
   • Myclobutanil (Immunox)
   • Propiconazole (Infuse)
   • Chlorothalonil (Daconil)
3. Resistant cultivars: 'Natchez', 'Muskogee', 'Tuscarora', 'Arapaho', 'Sioux', 'Tonto'.

Key Timing

Start fungicides when new leaves emerge in spring. Once heavy spotting appears in summer, fungicides only protect new growth—they don't cure infected leaves.

Your tree will likely reflush after defoliation. Focus on prevention next spring.