Tomato plants are a must in any garden. Disease can spoil the harvest. With these tips nothing stands in the way of a successful harvest.

Gray mold infests the tissues of the tomato and causes it to decompose

Many gardeners think that the only way to prevent tomato diseases is to use chemicals or new F1 varieties. In this article we will show that this is not true!

Fungus diseases in tomatoes

It is important that even as a hobby gardener you have a good overview of the antagonists of the tomato. This is the only way it is relatively easy to detect an infestation at an early stage or to prevent it immediately. A major problem when growing tomatoes, for example, is fungal diseases.

Tomato late blight

In most cases it is probably an infestation of tomato late blight and brown blight. This disease is caused by a fungus (Phytophthora infestans) and mostly occurs when culture conditions are too humid.

  • Symptoms:
    In midsummer, usually shortly before harvest, the leaves wither first, followed by the tomato fruits turning brown. As the name of the disease suggests, affected fruit appears rotten.
Brown rot can affect the fruit as well as the leaves and stems of the tomato
  • Prevention:
    The fungal spores often lie loosely on the soil, which means that splashes of water can transfer the spores to the lower leaves and fruits. If the cultivation conditions are damp (rainier summer, poorly ventilated greenhouse) the fungus can spread quickly and kill the entire plant within a few weeks. To prevent this, tolerant varieties can be sown/planted, or the plant can be protected from rainfall with a tomato canopy. When using used plant sticks, they should be thoroughly disinfected so that possible fungal residues from the previous year do not infect the young plant. Tomato plants should also be watered directly at the root area. Wetting the leaves with water can massively promote the fungal infection. In addition, tomatoes should be planted at a clear distance from potatoes. If your tomato plant has already formed a lot of leaves, thenyou should remove the lowest leaves at the bottom. This will avoid contact between the wet soil and the leaves. If the leaves of the tomato are in contact with the wet soil for a longer period of time, then the infestation with late blight is almost inevitable.
    WARNING: Especially without a rain cover, we consider the often-recommended maxing out to be counterproductive. When you pinch, you hurt the tomato. The wound is a gateway for all sorts of diseases. If you still want to pinch the side shoots, please only carry out this step in dry weather.
  • Treatment:
    If you recognize the infestation, you can usually only contain it. Infested plant parts cannot recover and should be removed immediately and disposed of with the residual waste. It can also be sprayed (preventively) with a copper preparation (e.g. Funguran) or another fungicide to control the infestation. There are also biological alternatives. After all, you don't want any spray residue in your food. Here you can either prepare a broth made from rhubarb leaves or use a commercial product like Neudovital.

The following resistant tomato varieties have proven themselves in our garden:

  • 'Primavera': Bright orange-red fruits that are bursting and particularly juicy and fruity. Good resistance to late blight and late blight.
  • 'Phantasia': F1 hybrid for outdoor and greenhouse use. Natural, high resistance to brown rot.
  • 'Pyros': F1 hybrid beefsteak tomato. Highly tolerant cultivar to late blight and late blight. Pleasantly spicy-fruity pulp.

Gray mold on tomatoes

This common rot in tomatoes is also caused by a fungus (Botrytis cinerea). Transmission is usually by wind or splashing water. The fungus has an easy time of it, especially in damp and wet climates, dense stocks or weakened plants.

  • Symptoms:
    This type of fungus can affect all parts of the tomato. First, the fungus forms brown spots, which quickly expand into a large, area-wide, gray mold lawn, especially in warm, humid weather. If you don't act quickly enough, the entire plant will die off within a short time.
Blight and late blight have different faces depending on the stage
  • Prevention:
    Plants should not be too close together, otherwise the plants will suffer from a lack of light and will grow more slowlyDry off in rain showers. A certain amount of airflow should be ensured between the plants.
    As already mentioned for late blight, tomatoes must be watered carefully in the root area. The foliage of the tomato plant must not be wetted.
    You should also be careful when fertilizing tomatoes. Even if the nightshade plant is one of the heavy consumers, over-fertilization with nitrogen weakens its resistance to fungal diseases.
    Even though many gardeners still regularly pinch their tomatoes, you should know that diseases can more easily penetrate the plant at these wounds be able. Pinching should only be done when cultivating in a greenhouse or under a tomato canopy. If the plants are not protected from rain showers, in our experience they should not be exhausted. Here it is advisable to increase the root mass (place the plant horizontally in the soil when planting out and tie the upper third of the shoot to the vertical) so that the additional stinging shoots can also be supplied with sufficient nutrients.
  • Treatment:
    In the early stage, the affected parts of the plant should be removed generously. The clippings must be disposed of with the residual waste and must not end up on the compost heap. The remaining tomato plant should then be as sunny and airy as possible. If possible, you should try to protect the plant from precipitation with a rain cover/roof.
    If the tomatoes are still a few weeks away from ripening, you can also consider using a fungicide to prevent further infestation. In any case, follow the instructions for use, which state which waiting times must be observed. In addition, the plant can be strengthened with some home remedies. Here, for example, a horsetail extract can be used.

Leaf spot

A fungus (Septoria lycopersici) is also up to mischief with this somewhat less common disease. Tomatoes are often only affected if celery is growing in the vicinity, as this is quite commonly infested.

  • Symptoms:
    Symptoms for this fungal disease are watery spots (mostly on the lower, older leaves) that are dark in color. An outer ring separates the spots from the still he althy leaf. This also yellows after a short time. The leaf then dies off. In the advanced stage you can also see the so-called spore receptacles on the underside of the leaf.
Here you can see the infestation of tomatoes with theLeaf spot Septoria [photo. Olya Maximenko/ Shutterstock.com]
  • Prevention and control:
    As with most other fungal diseases, damp and wet weather conditions greatly encourage fungal infestation. Tomato plants should be as dry and airy as possible and should not be wetted with water when watering. It is best to water carefully in the root area.
    Leaf spot disease in tomatoes is far less serious than the two diseases mentioned above. Infested leaves are quickly disposed of in the residual waste.
    Infestation usually weakens the plant and results in a smaller harvest. Complete failure due to leaf spot disease is extremely rare in tomatoes. To prevent the fungus from spreading further in bad weather, a pesticide and a plant strengthener (e.g. horsetail extract) can be used.

Tomato powdery mildew

This fungus (Oidium lycopersicum) is usually only found on tomatoes in a greenhouse culture. Powdery mildew doesn't get its nickname "fair-weather fungus" for nothing. It thrives especially during long periods of good weather and drought. Prevention is the best remedy for this fungus. Water regularly and make sure the greenhouse is not bone dry. In the event of an infestation, you can usually safely leave a pesticide in the closet. The affected leaves can be removed. If the infestation is a little stronger, you can also spray with Neudovital, for example.

This tomato leaf is infected with powdery mildew

Tomato early blight

The fungus (Alternaria solani) causes early blight. This is particularly evident in the fruits. Some of these become rotten. As a result, white mold develops, with black spores in the final stage. The foliage of affected plants should be kept as dry as possible. Infested fruit must be removed and disposed of in general waste before the spores can spread further. In general, the crop rotation for tomatoes must be observed. As a preventive measure, you can strengthen the plant with a horsetail extract or resort to a pesticide. Mixed cultivation with cruciferous vegetables (various types of cabbage) and carrots is also recommended.

The early blight is similar to brown rot

Velvet spot and brown spot disease in tomatoes

This tomato disease is only known to garden owners who have enjoyed the benefits of a greenhouse. Because theVelvet spot and brown spot disease only occurs in greenhouse cultivation. Cladosporium fulvum, a fungus that causes this disease.

  • Symptoms:
    The symptom is yellowish spots on the upper side of the leaf. These turn brown as the disease progresses and lead to the death of the affected leaf. A velvety fungal fluff forms on the underside, from which the spore deposits later develop.
The fungus spreads through spores in the tomato crop
  • Prevention:
    Damp leaves and high humidity promote an infestation with velvet spot disease. Plants should therefore be watered carefully in the root area. The leaves should never be wetted with water. Sufficient ventilation is also important. We therefore recommend greenhouses with sufficient height and numerous ventilation options. It is also important that the plants are not too close together and that air can circulate between the plants. Thinning out the tomatoes can also be useful.
  • Treatment:
    Velvet blotch has been on the rise for several years and is spreading quite quickly. Since it is difficult to combat the fungus with biological pesticides, you have to pay attention to prevention. The velvet spot disease should not be underestimated. Once it has spread in the greenhouse, it becomes difficult to permanently eliminate the pathogen. If you recognize an infestation, you must act quickly. Affected plant parts should be cut out over a large area and disposed of with the residual waste. To prevent it from spreading to other parts of the plant or other plants, a fungicide should be used to be on the safe side. The velvet spot disease should not be underestimated. Once it has spread through the greenhouse, it becomes difficult to eradicate the pathogen permanently.

Tomato wilting

Withering fungi (Fusarium, Verticillium, Pythium, etc.) are feared in commercial fruit, grain and vegetable growing.

  • Symptoms:
    The symptoms vary depending on the type of fungus: Fusarium fungi usually spread upwards from the lower leaves. The plant dies after about two weeks. Verticillium usually only affects other nightshade plants such as peppers and chili. In our opinion, however, it cannot be ruled out that the fungus will spread to neighboring tomato plants. Pythium shows up in the upper root area.This fungus massively weakens older plants and can lead to the death of younger specimens.
    Risk of confusion: Also a bacterial infestation with (Corynebacterium michiganense, Clavibacter michiganensis ) can lead to the typical wilting phenomenon.
Fusarium wilt is often only visible on one side of the tomato plant
  • Prevention:
    Particular preventive measures are essential. The culture conditions should not be too humid. This affects both the air humidity and the wetting of above-ground plant parts with irrigation water. Over-fertilization with nitrogen must also be avoided. It is essential to follow the crop rotation, since many wilt fungi are among the soil-borne diseases and can survive in the soil for several years. If you already had a fungal infestation in the previous year, you should definitely use more modern and resistant varieties.
  • Treatment:
    Destroy the plant and, if possible, remove the top layer of soil and also dispose of it in the residual waste. Calcium cyanamide is then worked into the soil. Immediately afterwards, all garden tools used should be disinfected (shovel, scissors, etc.). In addition, Phacelia (colloquially also referred to as bee pasture or bee friend) can be planted in the post-culture for soil treatment. No plants from the same family should be grown at the affected location for the next 5 years (observe crop rotation!). So that the pathogens can be broken down in the soil, he althy soil life is of great advantage. The introduction of compost or green manure promotes soil life.

Viral Diseases

In addition to fungal diseases, the following viruses also cause problems for tomatoes.

Tomato and Pepper Mosaic Virus

Two types of virus in particular are known here. The tobacco mosaic virus, once feared in tobacco growing, can also affect nightshade crops such as tomatoes, peppers/chillies and eggplant. An infestation usually manifests itself on the tomato fruits. Brownish rings form here. The flesh hardens and does not soften even when fully ripe. Apart from strengthening the plants, there is relatively little that can be done to prevent the infestation. Infested plants and fruits should be disposed of with household waste as soon as possible. If the infestation occurs more frequently in your own garden, you should use newer tomato varieties that are resistant to the mosaic virus.

This tomato leaf shows infestation with a mosaic virus

Another virus strain of mosaic virus jumpsof paprika or chillies above. Especially when peppers and the like are cultivated together with tomatoes, these plants must be checked regularly for aphid infestation. Because this pest transmits the virus when sucking. If you fight the lice, the viral disease usually has no chance. Beneficial insects can also be used against aphids. Read more about this in our article Beneficial insects in tomatoes.

Tip: You can find out how to identify and prevent further environmental and physiological damage to tomatoes in our special article

Blossom end rot: when tomatoes rot

A less critical disease is blossom end rot. Especially with large-fruited tomatoes (ox heart and beefsteak tomatoes), an unsightly discoloration forms on the underside of the fruit. As the stage progresses, the fruit contracts slightly inwards. This problem occurs due to a calcium deficiency and can be easily remedied accordingly. A soil rich in nutrients and minerals is the basis for he althy plants. If the phenomenon occurs anyway, you should fertilize with a garden lime.

It's not just diseases that can affect tomatoes, pests can also sometimes affect the plants. In this article you can find out how to combat tomato pests such as aphids, fungus gnats and the like.

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Vegetables