Bacterial Speck
Pseudomonas syringae pv. tomato
Overview
Bacterial speck of tomato is caused by Pseudomonas syringae pv. tomato. It thrives in cool, moist weather and is especially troublesome in spring plantings and humid coastal or greenhouse environments. The bacterium spreads by rain splash, contaminated seed, and tools. Speck often appears earlier and under cooler conditions than bacterial spot. Fruit lesions reduce fresh-market quality even when foliage damage is moderate, making early prevention important for slicing and cherry tomatoes.
Symptoms
Leaves develop small, dark brown to black spots, often with yellow halos. Specks are usually tinier than bacterial spot lesions. On green fruit, tiny raised black specks appear and remain as cosmetic defects as fruit ripens. Severely infected seedlings may be stunted. Leaf spots can coalesce under prolonged leaf wetness, causing blighted areas. Cool nights with dew favor new infection cycles.
Environmental Conditions
Cool
Prevention
Use hot-water-treated or certified clean seed and inspect transplants. Plant after the coolest, wettest spring weather when practical, or protect early plantings under tunnels with good airflow. Mulch to reduce splash. Choose speck-resistant tomato cultivars for cool, humid regions. Sanitize stakes and clips between seasons. Keep nightshade weeds out of tomato areas to reduce early inoculum.
Management
Roguing heavily speckled seedlings before transplanting. Switch from overhead irrigation to drip. Copper products and some biopesticides can reduce surface populations when applied before rainy periods, but they will not erase existing lesions. Avoid working wet plants. Remove lower leaves that stay wet near soil. After cool, wet springs with heavy speck, clean up debris and rotate tomato beds when possible.