Bacterial Speck of Tomato Plant : Prevention & Management

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Quick Answer: Bacterial Speck of Tomato Plant

The bacterial speck of the tomato plant is a gram-negative bacterial disease. It damages tomatoes in cold and wet weather. It is an air-borne bacterium. It produces greasy spots on the leaves of the tomato plant. The use of resistant cultivars is an effective way of preventing bacterial speck. Biological methods can be used to keep a check on the disease.

This is a detailed guide on the Bacterial speck of the tomato plant – what causes it, how to identify and how to take care of it.

Let us get started!

What is Tomato Bacterial Speck Disease?

The bacterial speck of the tomato plant is a bacterial disease caused by Pseudomonas syringae. 

It is a gram-negative bacterium. 

Pseudomonas syringae grows at a temperature range of 13 and 28°C; developing optimally at 75°F or 18–24°C.  The symptoms of the bacterial speck are not noticed at 89°F or above 30°C. The bacteria flourish in cool and moist weather. 

The bacterial speck pathogen can prevail in the soil debris or on plant debris for 7-8 months. It is found in the debris of earlier infected tomato plants or regrowths of old tomato plants.

According to some studies, Pseudomonas syringae strives on the roots and foliage of weeds such as Amaranthus, Chenopodium, Hibiscus, Polygonum, and Stellaria.  

How does Bacterial Speck Spread in Tomato Plants?

This is an air-borne disease and is disseminated by aerosols or water splashes. The disease is spread through contaminated seedlings or contaminated tomato plants. 

The transmission is supported by garden tools, infected hands, or shoes. High humidity and moderate temperatures support the development of the bacteria.

The spread of bacterial specks within the tomato garden is facilitated by overhead watering, water splashes, and infected stakes or rods.

The contact of one tomato plant with another tomato plant may result in the spread of disease to healthy tomato plants.

Check out this video on the bacterial speck-

How do Bacterial Speck Harm Tomato Plants?

The bacteria enter the intercellular spaces of cells and tissues after entry from stomata and multiply in the tissues in large quantities under advantageous weather conditions.

The circumstances that favor the growth and development of Bacterial specks in the tissues are cold climate, high humidity [≥ 80%], moderate temperature [64- 75°F], water-filled aerosols, and conditions of crop. 

Studies suggest that some of the bacterial colonies are found on hairs in the ovaries of the tomato plant. These hairs protect the ovaries during pollination and after pollination vanishes.

The entry points which were occupied by hairs are now left open and act as the source of entry for the bacteria. 

These clusters of bacteria then invade the epidermis of the young, green tomato fruits.

How to Confirm that Bacterial Speck is Troubling your Tomato Plants?

Bacterial speck pathogen takes five to six days to develop before it invades the cells and begins to show the symptoms. The signs of the bacterial speck are found on leaflets, stems, petioles, and fruits.

Bacterial speck infects green and ripened tomato fruits.

You can differentiate bacterial speck disease from any other bacterial infections by observing the following signs on leaves –

Brown to black and tiny greasy stains are found on the bottom young leaflets of the plant. These spots range from 0.3-0.6 cm in diameter. These spots develop on the abaxial side of the leaf.

A yellow halo surrounds the damaged zones. It is circular, angular, and is of non-uniform size. Long durations of foliage wetness result in lesions of 2–3 mm. The lesions coalesce, become necrotic and the leaf dies. 

Stems and petioles show small, oval-shaped spots. These spots enlarge and infect the entire leaf in a short period. Ultimately, stems develop dark brown lesions and coalesce.   

Eventually, the disease progresses and infects the fruits of the plant. Fruits show black, tiny [1/16th inch], flat, and sunken specks. Finally, the fruit drops.

Check out this video for Bacterial Speck of the tomato plant –

Ways to Control Bacterial Speck Disease on Tomato Plant

There is no cure for the bacterial speck but you can manage the disease through some easy practices.

1. Copper Bactericides

Copper shows an excellent preventive effect on the bacterial speck of the tomato plant. Bactericides containing salts of copper like copper sulfate, copper hydroxide, cuprous oxide, and copper oxychloride are used to reduce the spread of the disease.

Copper salts work great with other chemicals such as maneb or mancozeb. Preventative bactericides containing these mixtures would help to decrease the development of the disease.

Spraying bactericide during sunlight may burn your foliage. Always check the instructions before the application of the fungicide. 

Another chemical that can be used preventatively is sodium hypochlorite.

It is recommended to spray the bactericide within 4 days of disease onset and repeat the treatment after every 5-6 days.  

2. Seed Treatment

Bacterial speck is largely spread by infected seeds or seedlings. It becomes mandatory to disinfect the seeds using various methods. To remove bacterial cells from the seeds, one should-

Keep the seeds in hot and dry hair for almost a week. Keep it at a temperature above 50 degrees Celsius. This will keep a check on seed germination.

You can soak the seeds in 0.8% acetic acid, 5% hydrochloric acid, sodium hypochlorite at 1.05% for 20–40 minutes, and mercuric chloride at 0.05% for 5 minutes. This will help if the contamination is external.

3. Soil Solarization or Soil Fumigation

Soil sterilization reduces the chances of bacterial specks by almost 30%. These methods can eradicate the bacterial colonies up to 30 cm deep. 

  • Mulch your soil with polythene sheets.
  • Keep the layer of mulching for almost a month.
  • Wet your soil for at least 10-12 inches deep.
  • Keep the mulched soil in sunlight.

Soil solarization is an eco-friendly thermal killing method. It requires a constant supply of water and heat.

It ensures the killing of deep-buried weeds, nematodes, viruses, bacteria, or fungi. 

4. Plant Resistant Cultivars

The use of tomato varieties resistant to bacterial speck is the most practical way of controlling the disease.

Ontario 7710, Ontario 7611, and Ontario 782 showed good resistance for a bacterial speck of the tomato plant.

Check out this video on gene resistance for bacterial speck-

5. Use Essential Oils

According to some studies, essential oils such as tea tree oil, Thyme oil, Citronella oil, Eucalyptus oil, and lemongrass oil with copper bactericides have reduced the risk of bacterial speck 8-40%.

How to Prevent Bacterial Speck on Tomato Plant

The best way to protect your plant from bacterial speck disease is by adopting some preventative measures.

These measures could be performed during the harvest, after the harvest, or before the harvest of the tomato.

1. Steps You Can Take During the Harvest

Avoid sprinkling of water. 

Water your plants very gently. Do not perform overhead watering. Build trenches if necessary, it will ensure water absorption by roots and reduce chances of foliage wetness.

Restrict working with your plants when they are wet. 

Do not perform any movement in your garden during cool and moist conditions. 

Ensure proper drainage, sufficient sunlight, and good ventilation for your tomato plants.

The best way to achieve these requirements is by mulching, staking, and caging plants.

Do not plant two tomato plants together. 

2. Before harvesting

Handle your seeds very carefully.

Plant the seeds very gently. Avoid injuries due to tools.

Remove all the weeds and plant debris from the ground. Sterilize your soil using heat soil treatment.

Avoid planting the tomato seeds in cold and humid seasons.

3. After harvesting

Do not replant your tomato plants in the same area.

Disinfect garden tools with 10% bleach or 70% alcohol.

Burn all the infected plant leaves, stems, or fruits in a burn pile. Do not compost the plant residues. 

For the next harvest, provide your plants with adequate but not excessive nitrogen; enrich the soil organic matter through animal waste, or cover crops.


How do we differentiate between bacterial spots and bacterial speck of the tomato plant?

You can observe the fruits of the tomato plant for confirming bacterial speck. The green fruits infected with bacterial speck shows tiny black spots. They have a diameter of 1mm. These spots are surrounded by dark green halo on ripened red fruits.

Are tomatoes with bacterial speck safe to eat?

Yes, tomatoes with bacterial speck are safe to eat. There is no cure for a bacterial speck on tomato plants but fruits are completely healthy and fit. However, they won’t be firm, red tomatoes with appealing skin but they will be totally edible. 

Can I reuse the soil infected with bacterial speck?

Bacterial speck is an air-borne disease. No study suggests that bacterial speck can be transmitted through infected soil. However, this disease is spread through plant debris and water splashes so, it is advised to sterilize your soil using soil solarization or soil fumigation. It will reduce the risk of bacterial speck or any other soil-borne disease. 

What is the appropriate time for watering the plants?

Always water your plants in the morning. 


I hope this guide on Bacterial Speck disease of the tomato plant has helped you with the management of disease in the garden.

Do share this guide with other gardeners!