bacterial spot on a tomato leaf

Bacterial Spot symptoms on a tomato leaf. Photo: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org

Updated: February 20, 2023

Two types of bacterial diseases occasionally damage the foliage and/or fruits of tomato plants: Bacterial Spot and Bacterial Speck.

Bacterial Spot

  • Symptoms: small, dark spots (⅛ inch or less), sometimes water-soaked or wet-looking spots; leaf yellowing and leaf loss; fruits develop small, dark raised blisters that can enlarge and become scab-like.
  • Cause: Four types of Xanthomonas sp. bacteria. These pathogens can be transmitted by seeds and transplants.
yellow and tan irregular spots on a tomato leaf
Bacterial Spot (Xanthomonas vesicatoria) on a garden tomato leaf. Photo: Florida Division of Plant Industry, Florida Department of Agriculture and Consumer Services, Bugwood.org  
brown spots on a tomato
Bacterial Spot symptoms on a tomato. Photo: Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org

Bacterial Speck

bacterial speck lesions
Symptoms of Bacterial Speck on tomato leaf. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
  • Symptoms: small black spots (⅛ inch or less), more prominent on leaf undersides, older spots may develop yellow rings; tiny spots or specks on the surface of tomato fruit, may be raised or sunken.
  • Cause: Bacterium, Pseudomonas syringae pv. Tomato

For both diseases

  • Spots coalesce during warm, wet, and humid weather and turn brown.
  • Leaves will drop with severe infections, resulting in sunscald.
  • The bacteria overwinter on crop residue and are seed-borne.
  • The disease is spread by splashing rain and working with wet, infected plants. Hot, dry weather will slow the spread of this disease.

Management

Select disease-resistant tomato cultivars. Buy clean, disease-free seeds from a reputable supplier. If the seeds have not been chemically or heat-treated, soak the seeds for five minutes in one pint of water and add two ounces of bleach. Rinse seeds thoroughly with clean, cool water and dry thoroughly.

Cover the soil around plants with mulch and do not crowd plants together. Avoid overhead watering and working with plants when the foliage is wet. Fertilize plants to support new growth. Spray with a labeled copper fungicide when symptoms are first observed. Remove infected plants and dispose of all infected crop residue. 

Related information

Vegetable Problems Caused by Nonliving Factors

Vegetable Problems Caused by Insects

Vegetable Problems Caused by Wildlife

Author: Jon Traunfeld, Extension Specialist, Vegetables/Fruits, University of Maryland Extension. Revised 11/2022

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