Tomato black bacterial spot

Pathogen and disease type. Tomato black bacterial spot is a destructive plant disease caused by the bacteria Xanthomonas vesicatoria. It is a highly contagious bacterial infection that thrives in favorable environmental conditions, causing necrosis on foliage, stems, and fruits, which significantly reduces overall crop yield and marketability.

Host range. This disease predominantly affects members of the Solanaceae family, including tomatoes and peppers. The pathogen is seed-borne and can also persist in crop debris or alternative weed hosts, making it a persistent challenge for commercial growers and home gardeners alike.

Symptoms and signs. The disease manifests as small, water-soaked spots that expand into irregular, dark brown or black necrotic lesions with yellow halos on the leaves. On fruit, the characteristic symptoms are raised, scab-like black spots that may eventually develop into deep, sunken pits, rendering the produce unsuitable for consumption or sale.

Development and spread. The bacteria thrive in warm, humid climates, especially when temperatures range between +25°C and +30°C. Rainfall, overhead irrigation, and high relative humidity facilitate the spread of bacteria through splashing droplets, which enter the plant tissues through stomata or mechanical wounds caused by pruning or insect activity.

Control and prevention measures. Effective management of bacterial spot requires a rigorous integrated pest management (IPM) strategy:

• Utilizing certified disease-free, treated seeds.
• Implementing strict crop rotation protocols to avoid field carryover.
• Minimizing canopy wetness by using drip irrigation and ensuring proper spacing.
• Removing and destroying infected plant material promptly to limit inoculum levels.
• Applying copper-based bactericides preventively to protect the foliage during vulnerable growth stages.