Home > Tomato > Bacterial Diseases > Bacterial Spot

Try our books

Integrating Animals for a Sustainable Garden
Buy
Learn More

Bacterial Spot

Bacterial spot is caused by a species of bacteria called Xanthomonas campesiris pv. vesicatoria. It can be a serious tomato disease and it is often confused with bacterial speck.

How It Spreads

Tomatoes usually become infected with bacterial spot because the seeds are infected or because the bacteria is washed or blown into wounds. The bacteria that causes this tomato disease can also survive over winter in decomposing plant matter and the soil to some extent. As a result of this, common causes of the spread of this disease include watering with a high pressure hose, growing plants from seeds saved from diseased fruit and planting tomatoes in soil that has recently (in the last 1-3 years) grown tomatoes or other nightshade vegetables.

Plants affected

Bacterial spot affects tomatoes and other members of the nightshade vegetables (such as capsicum) as well as stone fruit (such as peaches and cherries).

Symptoms

Bacterial spot produces small, dark spots on leaves; often there is a yellow ring around the spots. Sometimes the spots join together and the leaves end up looking yellow all over - this is not as commonly seen in cases of bacterial speck, which is a similar bacterial tomato diseases. If plants are infected prior to flowering, the disease will cause the flowers to drop. Bacterial spot is best distinguished from bacterial speck by the symptoms that appear on the fruit. Tomatoes infected with bacterial spot develop small raised spots, which can grow up to 6mm (1/4 inch) across - this is larger than the spots seen when bacterial speck is the cause of the symptoms. The spots associated with bacterial spot are also usually slightly indented and often look like scabs. Fruit is usually infected when green - ripe fruit is usually pretty safe from the disease.

Bacterial spot is best distinguished from bacterial speck by the symptoms that appear on the fruit. Tomatoes infected with bacterial spot develop small raised spots, which can grow up to 6mm (1/4 inch) across - this is larger than the spots seen when bacterial speck is the cause of the symptoms. The spots associated with bacterial spot are also usually slightly indented and often look like scabs. Fruit is usually infected when green - ripe fruit is usually pretty safe from the disease.

Treatment

Spraying plants with an infusion of chives or garlic or with a copper or streptomycin (antibiotic) spray can help to treat the disease. Prevention is much more effective though.

Prevention

As with other bacterial tomato diseases the first step to preventing infection is to plant disease free seeds or seedlings. If you save your own seeds, soak them in hot (but not boiling) water prior to sowing to help kill any bacteria that may be present.

You should rotate your annual plants so that tomatoes and other nightshade vegetables aren't planted in the same spot for at least 3 years. It also helps to avoid planting tomatoes near stone fruit. Companion planting is also useful for building plant resistance to diseases and for preventing infection (choose companions with antibiotic properties such as mustard and onions).

Preventative sprays with a chive infusion or a copper or streptomycin solution can prevent infection. Care should be exercised when using such sprays, particularly the streptomycin one, to ensure that you do not contribute to the rise of antibiotic resistant bacteria.

This site works best with JavaScript Enabled.

© 2017 K. M. Wade | Contact: