This disease is characterised by spots on tomato leaves and it is often confused with bacterial spot which is very similar in appearance, though it is caused by a different species of bacteria. The bacteria that causes bacterial speck is called Pseudomonas syringae pv. tomato.
How It Spreads
The bacteria that causes bacterial speck can be passed from a tomato to seedlings through the seeds. Cool, moist conditions promote the growth and spread of the bacteria. The bacteria can also survive on nearby weeds, decomposing plant matter and in the soil for some time so planting repeat crops of tomatoes and using diseased plants as mulch or in compost are both significant methods for the spread of this disease.
Bacterial speck affects tomatoes and other nightshade vegetables such as capsicums. Any above ground part of a plant may be affected.
This tomato disease causes small black spots to appear on plant leaves. The spots often have a yellow ring around them. Bacterial spot produces very similar spots except that they often look greasy. In both diseases, tomato leaves curl but it is usually worse in bacterial spot. Both tomato diseases also affect the fruit. Bacterial speck produces very small, slightly raised spots on the tomatoes. These spots do not become scaly. If tomato plants are affected prior to flower production, flowers will fall off.
Copper or chive sprays may help to treat mild infections but it is better to prevent the disease in the first place.
The first place to start preventing bacterial speck is in the nursery - buy only certified disease free seeds or seedlings. If you're saving your own seed, soak your seeds in hot water (not boiling water) prior to planting to help kill any bacteria that may be present. Saving seed using the fermentation method can also help. Some tomato species are resistant to bacterial speck so it may be worth hunting these down if your area is prone to such diseases or if you've had problems with it in your garden in the past.
Practice crop rotation to prevent infection from bacteria that has over wintered in the soil. Companion planting can also prevent the disease (use antibacterial plants such as chives, garlic and mustard), reduce the spread of the disease and reduce weed infestations that can harbour the bacteria.
Preventative sprays using copper or chive/garlic infusions can help stop the bacteria from getting a hand hold but these should only be used first thing in the morning in order to minimise damp foliage. On a similar note, only water in the mornings.