Bacterial Leaf Spot

Bacterial leaf spot begins as small, water-soaked spots on leaves that enlarge and turn brown to black, frequently surrounded by a yellow halo. Heavily spotted leaves can yellow and drop, reducing canopy cover and fruit protection. On fruit, infection produces small, raised, scab-like spots that can affect marketability even though the fruit interior is usually unaffected.

The causal bacteria enter leaves and fruit mainly through natural openings such as stomata and through wounds, multiplying in the water-soaked tissue before lesions become visible. Because the bacteria need free moisture to move and infect, disease development is closely tied to rain, dew, and irrigation practices that wet foliage.

Rain splash and overhead irrigation

Move bacteria from infected to healthy tissue and between plants

Contaminated seed and transplants

Can introduce the pathogen into a previously clean planting

Crop debris and volunteer plants

Allow bacteria to survive between seasons in the field

Tomato and sweet pepper are the principal hosts of bacterial leaf spot, both susceptible to leaf, stem, and fruit infection. Related solanaceous crops and some weeds can also host the bacteria in certain regions, which can complicate management where these plants grow near production fields.

• Warm, wet, or highly humid weather, especially with wind-driven rain
• Overhead irrigation and working in fields while foliage is wet
• Use of infected seed or transplants
• Handling plants or equipment that move between infected and healthy areas
• Dense plantings with limited air movement

Because bacterial leaf spot spreads through water and contact rather than airborne spores, prevention focuses on starting with clean planting material, minimising foliage wetness, and limiting mechanical spread.

• Use certified, disease-free seed and transplants
• Choose resistant or tolerant varieties where available
• Avoid working in fields or handling plants while foliage is wet
• Use irrigation methods that minimise leaf wetting where practical
• Rotate away from tomato and pepper and remove infected debris and volunteer plants