Why Do My Pepper Leaves Have Brown Spots?

Brown spots on pepper leaves are usually a disease taking hold, and the type of spot tells you which one. Because these diseases spread by water and can climb through a planting, identifying yours and changing how you water makes a real difference. Let me show you how to read the spots and stop them before they strip your plant.

Bacterial leaf spot: the most common

The most frequent cause of brown spots on peppers is bacterial leaf spot. It shows as small, water-soaked spots that turn brown to black, often with a yellow halo around them, and they may have a slightly raised, scabby or angular look. Badly affected leaves yellow and drop, and the bacteria can spot the fruit too. It thrives in warm, wet, humid conditions and spreads in splashing water and on hands and tools. Because it is bacterial, there is no curative spray — management is about slowing the spread.

Fungal leaf spots

Various fungi also spot pepper leaves, producing round brown lesions, sometimes with lighter centres or concentric rings. Cercospora leaf spot, for example, makes circular spots with pale grey centres and dark margins — a "frogeye" look. Like the bacterial version, fungal spots thrive in warm, wet conditions and spread by splash, beginning on lower leaves and climbing. Fungal spots can sometimes be slowed with a protective fungicide, unlike the bacterial kind.

The treatment is broadly the same

Whichever you have, the response overlaps and you should start promptly. Remove affected leaves and bin them — never compost diseased foliage. Switch all watering to the base of the plant, in the morning, so you stop splashing the pathogen onto the leaves and any moisture dries fast. Improve airflow with generous spacing and by removing congested lower growth so leaves dry quickly after rain or dew. Never handle the plants while they are wet, since that spreads bacteria. For confirmed fungal spotting, a copper or appropriate fungicide on healthy leaves can help; copper also offers some suppression of bacterial spot.

Stopping it coming back

These diseases overwinter on debris and can ride in on seed, which is why they return to the same beds. Clear away all pepper debris at the end of the season, rotate peppers to a fresh spot for a couple of years, and start with disease-free seed and resistant varieties where available. Mulch the soil to reduce the splash that carries pathogens up onto the lowest leaves. With clean seed, rotation, dry-leaf watering and good airflow, brown leaf spots can be kept to a minor issue.

Telling it from harmless marks

Not every mark is disease. Sunscald can bleach and brown patches on exposed leaves, nutrient issues can mottle them, and physical or cold damage leaves dry marks that do not spread. The way to tell: disease spots are usually defined, often haloed, and they multiply and climb the plant over days, while harmless marks are static. If the spots are spreading and increasing, treat them as disease and act on the watering and airflow first.