Cercospora Leaf Spot: Identification, Host Range & Fungicide Management

Cercospora leaf spot, caused by Pseudocercospora (formerly Cercospora) species, affects a wide range of crops—citrus, beans, beets, peppers, carrots, okra, roses, avocado, fig, coffee, watercress, and more. The fungus overwinters in infected debris; wind and rain splash spread conidia in warm, wet weather. Management combines sanitation, rotation, and timely fungicides.

Symptoms by Crop

• General: Circular leaf spots with gray-tan centers, dark margins, yellow halos; centers may fall out (shot-hole).
• Citrus (fruit): Dark, sunken, tumor-like spots with halos; necrotic, woody flesh; premature drop.
• Roses: Dark sunken lesions on leaves; defoliation.
• Okra: Sooty mold on leaves.
• Carrots: Necrotic spots on young leaves.
• Stems/twigs: Less common; twig dieback possible.

Disease Cycle

1. Overwinters in infected leaves, fruit, debris on ground.
2. Spring warmth + rain → conidia production.
3. Spread: rain splash, wind, mechanical (tools, hands, insects).
4. Infection: requires leaf wetness; optimal 77–86°F (25–30°C).
5. Multiple cycles per season in humid climates.

Management

Cultural (Foundation)

• Fall cleanup: Remove and destroy all fallen leaves, fruit, debris—primary inoculum source.
• Crop rotation: 2–3 years away from susceptible crops (especially in same family).
• Spacing & pruning: Maximize airflow; reduce leaf wetness duration.
• Irrigation: Drip only; avoid overhead. If overhead, water early morning.
• Resistant varieties: Available for some crops (beans, beets, peppers)—select them.

Chemical (When Needed)

• Start at first sign of disease in warm, wet season.
• Rotate FRAC groups annually to delay resistance (e.g., QoI → DMI → SDHI → multi-site).
• Common actives: chlorothalonil (M5), copper (M1), mancozeb (M3), azoxystrobin (11), difenoconazole (3), boscalid (7).
• Second application often needed in prolonged wet/humid periods.
• Follow label: rate, interval, PHI, max applications.
• Consider licensed applicator for commercial crops.

Post-Harvest

• Destroy heavily infected crop residue in fall.
• Do not compost diseased material unless pile reaches sustained 140°F (60°C).

Cercospora rarely kills outright but ruins marketable yield and quality. Clean fields, resistant genetics, and smart fungicide rotation keep it below economic thresholds.