Black Spots on Pepper Leaves: Fungal Diagnosis and Sulfur Treatment

Identifying and Treating Pepper Leaf Spot Diseases

Black spots with yellow halos on pepper leaves that eventually drop indicate fungal infection—likely Alternaria leaf spot, Cercospora, or bacterial spot. Soil-borne or splash-dispersed, these pathogens thrive in warm, humid conditions.

Immediate Action: Sulfur Treatment

1. Foliar spray: Wettable sulfur (1 tbsp/gallon) applied weekly, covering both leaf surfaces. Avoid applications above 85°F to prevent phytotoxicity.
2. Soil drench: Same sulfur solution applied to root zone every 2 weeks to suppress soil-borne inoculum.
3. Remove and destroy severely infected leaves—don't compost.

Cultural Controls

• Mulch heavily (straw, black plastic) to prevent soil splash
• Stake plants to improve air circulation
• Water at soil level only—never overhead
• Rotate peppers out of this bed for 2-3 years

Resistant Varieties for Future Plantings

Look for cultivars with resistance codes: BLS (bacterial leaf spot), CMV (cucumber mosaic virus), TMV (tobacco mosaic virus). 'Ace', 'Aristotle', and 'Revolution' offer good disease packages.

When to Suspect Bacterial vs. Fungal

Bacterial spots often have distinct yellow halos and appear water-soaked initially. If sulfur doesn't slow spread in 10-14 days, switch to copper-based bactericide (e.g., copper hydroxide) and submit a sample to your extension office for confirmation.

Early, consistent sulfur applications combined with strict sanitation usually contain pepper leaf spots without yield loss.