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Common Tomato Plant Diseases

30-Oct-2013 | Contributed by: Guest Author

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Tomato plants are relatively hardy, but like any plant, there are particular diseases that they are susceptible to.

To reduce the risk of soilborne diseases, practice crop rotation, but rotating your tomato plants so they don’t grow in the same ground every year.

Most fungal disease can be prevented by watering at the base of the plant (instead of overhead) and by avoiding overcrowding.


This is a fungus that affects the fruit. It looks like a circular, discoloured, and indented area on the fruit. It causes the flesh to rot through, particularly on tomatoes that are overripe.

It is common in warm, wet weather, and is spread by rain spash.

Water at the base of the plant and avoid overcrowding to help prevent this disease. Pick fruit as they ripen rather than waiting to prevent the rotting.

Blossom End Rot

If the fruit looks sunken at the base, and is leathery and brown, your plant may have blossom end rot.

Prevent blossom end rot by watering regularly (instead of in peaks and troughs), mulching, and by adding lime before planting.

If your plant is affected by blossom end rot, remove the affect fruit and keep the plant well watered.

Early Blight

This fungus usually occurs once the plant begins to fruit, and causes leaves to have brown or black spots. In fruit the stem can be affected, with large black areas.

To prevent this, water at the base of the plant and avoid overcrowding.

Late Blight

Late blight often occurs in cool, wet weather towards the end of the growing season. It causes irregular papery patches on the leaves, and irregular brown patches on the fruit that can become rotten.

Prevent late blight by watering at the base of the plant and by avoiding overcrowding.

Mosaic Virus

This common virus lowers the number of fruit, and their quality. It causes a mottling of green and yellow on the leaves and fruits.

Avoid handling your plants as the disease must enter through a cut, and if you smoke, wash your hands before handling as tobacco can transmit it.

Septoria Leaf Spot

This common disease affects the leaves of the plant. It causes small spots that have grey centres and dark edges. The leaves will yellow and wither before falling off.

Water at the base of the plant and avoid overcrowding to help prevent septoria leaf spot. 

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