Tomatoes - Pests and Diseases

Although tomatoes are relatively easy to grow, there can be problems with a variety of pests and diseases.

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  • Aphids - there are a number of pesticides available to combat aphids. I wouldn't use them when there is fruit on the plants, though. An organic way of dealing with them is to spray with soapy water.
  • Greenhouse whitefly- use the same methods as for aphids.
  • Potato cyst eelworm - rotate planting so tomatoes (and potatoes) are not planted in the same place every year.
  • Tomato Mosaic Virus -symptons are mottled yellow curled leaves sometimes with brown steaks on the stems. The only thing to do is to destroy the entire plant including roots and fruit. Don't put it in the compost, it is better to burn it.
  • Pototo Blight - usually seen only on outdoor plants. Symptoms are brown patches on leaves with dark brown streaks on stems. In severe attacks, white threads can appear on the underside of leaves. Again, destroy the entire plant.
  • Leaf Mould- only affects greenhouse grown plants. Symptoms are a grey to purple coloured mould on the underside of leaves with brown marks on the tops. It occurs when there is insufficient ventilation and the greenhouse becomes too humid. Remove leaves as soon as you see the mould and destroy the plants as soon as tomatoes ripen. Do not put plants or leaves on the compost heap. When the tomatoes have finished, wash the greenhouse down with something like Jeyes Fluid.
  • Didymella Stem Rot- usually seen on greenhouse plants. Symptoms are irregular slimy black circular lesions on stems close to the ground. Destroy affected plants and spray the bottom of stems of the remaining plants with a copper based fungicide. When the plants have finished and tomatoes ripened, destroy them, do not compost. Rotate tomato plants every year or two to prevent attacks.
  • Blossom End Rot - symptoms are brown or black patches that can become leathery at the flower end of a developing tomato (the opposite end to the stem). It is caused by a lack of calcium and can occur after a period of drought conditions. Prevention is better than cure in this case, so avoid letting tomatoes become too dry.
  • Phytophthora Stem Rot - Symptoms are brown or black fungus on the main stems, often succeeded by white, cottony growth. Destroy affected plants, do not compost. The soil should be replaced or sterilised before using again.
More on Tomatoes
Growing Tomatoes
Seeding and Planting Tomatoes
Troubleshooting Tomato Problems
Tomato Recipes

There is another common problem not caused by pests or diseases:

Skin splitting on tomatoes

This can be a combination of cold weather and irregular watering. In cool conditions, the fruit develops slowly and the skins becomes tough. When they then have a dry spell followed by plenty of water, the skin can't expand to accommodate it and splits. Although they don't look very appetising, the tomatoes can still be eaten.

Also see Garden Pests and Diseas


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