Bacterial Spot is caused by several species of Xanthomonas. The bacteria can survive on infected seed and plant debris and spread readily by splashing rain, irrigation, contaminated tools and handling wet plants. Warm, wet weather strongly favours infection. Small water-soaked spots develop on leaves, becoming dark and sometimes surrounded by yellow tissue. Severe infection can cause leaves to yellow and drop. On peppers and tomatoes, fruit may develop raised, rough, scabby lesions that reduce quality and can provide openings for other organisms.

How to Fix It
Remove infected material: Remove badly affected leaves and plants and dispose of them rather than composting them.
Keep foliage dry: Water at soil level and avoid overhead watering.
Don't handle wet plants: Working among wet plants can spread the bacteria from plant to plant.
Improve airflow: Give plants adequate spacing and control weeds so foliage dries quickly.
Clean tools: Disinfect pruning tools and other equipment used around infected plants.
Rotate crops: Avoid planting peppers or tomatoes in the same location for at least 2–3 years.
Start clean: Use disease-free seed and healthy transplants; infected seed is an important way the disease is introduced.
Choose resistant varieties: Resistance is available in some pepper and tomato varieties, although resistance varies among bacterial-spot strains.