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Tomatoes are one of the most popular vegetables to be grown in gardens and on balconies. Although they are not very sensitive, they can make tomato diseases inedible and, in the worst case, destroy an entire year's crop. Typical characteristics make it easy to recognize the various diseases and these can be prevented with practical tips and professional care instructions.

tomato diseases

Tomatoes are relatively easy to grow and often delight hobby gardeners with a bountiful harvest. It is annoying when tomato diseases spread. Care mistakes are often made, but despite the best conditions, tomatoes are not immune to diseases and pests. The damage images can vary. Here it is important to recognize them quickly in order to initiate the right treatment and, ideally, to save your harvest. With the right care tips, you can prevent tomato diseases.

Tomato disease on a green tomato

fungal diseases

Care tips for prevention

  • Keep leaves dry when watering
  • early removal of side shoots
  • Separate tomatoes into single shoots using a stick or string
  • Disinfect sticks at least once a year, preferably after the gardening season

Early Blight (Alternaria solani)

Early blight is a fungal disease. It is one of the most common fungal species in tomato diseases. The fungus is usually active between June and August. The fungal pathogen "Alternaria solani" is transmitted by wind. These tend to settle on wooden sticks and in the ground. From there, the fungus spreads to the tips of the leaves.


  • Fungal infestation usually starts at the bottom and slowly moves up
  • black spots form on the upper sides of the leaves
  • black spots are mostly bordered by leaf veins
  • the calyx area and fruit begin to rot and mold
  • Leaves curl up and fall off
  • Tomatoes become soft to mushy


Once this fungus has settled, the plant can only be saved if the damage is minimal and the spread is limited. Treatment is always advisable to contain the fungus and prevent transmission to neighboring plants. You can do this with a fungicide, such as CELAFLOR® Saprol Vegetable Fungus Free. You should also check the location. If the tomatoes are too warm at over 20 degrees Celsius and too damp, this favors early blight and other diseases. A transplant is dry soil and a cooler environment will keep the fungus at bay.

Tomato plant with mottled leaves

TIP: As a rule, do not dispose of tomato plants with fungal diseases that cannot be saved in the compost, but in household waste.

Preventive measures:

  • Do not plant tomatoes next to potatoes - these attract the Alternaria solani pathogen
  • Cut leaves regularly to a height of between 25 centimeters and 30 centimeters
  • Trim tomato plants regularly (remove new shoots)
  • ensure good ventilation and a dry location

Powdery mildew (Oidium neolycopersici)

Powdery mildew includes a species of fungus that is common among tomato diseases. This usually affects the leaves and plant tissue. If left untreated, it can cause serious damage that can lead to the death of the tomato plant. It usually occurs between May and August.

powdery mildew on plant leaf


  • Infestation mainly on the leaves and petioles
  • white, sticky spots on the upper surfaces of the leaves
  • white spots merge into one another as the disease progresses
  • Leaves turn yellow and brown before drying up
  • growth disorders


A very effective and ecological control agent is soapy water made from natural soap without additives. Make a highly concentrated suds from the soap and water. Splash the affected plants with it until dripping wet. Repeat the process again after two or three days. If fungal spores are still visible, you can spray again with the soapy water after a week. The powdery mildew should have died by then at the latest.

Alternatively, you can use a fungicide. Here you have to make sure that it is suitable for edible vegetables, otherwise you will lose the harvest. Parts of the plant that show signs of damage from fungal diseases should always be cut off after treatment, regardless of whether the treatment was carried out with soapy water or a fungicide.

Preventive measures:

  • Choose varieties that are more resistant to fungal tomato diseases, such as Phantasia F1
  • ensure constant ambient temperatures
  • if possible, keep humidity below 70 percent
  • Potassium fertilizer prevents infestation

Gray mold (Botrytis cinerea)

Gray mold is a mold that is transmitted by the pathogen Botrytis cinerea. This fungus is also known as ghost spot disease. The harmful symptoms of diseases of this fungus extend over the entire plant, including the tomato fruits. It mainly spreads between May and September and likes high humidity, which is why it usually feels particularly comfortable in greenhouses.

Botrytis infection on a plant stem


  • gray spots on the leaves and stems of tomatoes
  • in the advanced stage, a carpet of spores spreads
  • Stems and tomatoes go moldy


Only tomatoes whose tissue has not been damaged can be saved. Otherwise the plant must be disposed of completely. If there is still undamaged tissue, you can take the following measures to treat fungal tomato diseases of this type.

  • Cut back all parts of the plant to the healthy area
  • In the case of advanced infestation, use a fungicide such as Bayer Infinito Vegetable Mushroom-Free
  • discard moldy tomatoes

Preventive measures:

  • not near plants that tend to grow fungi, such as strawberries, raspberries or lettuce
  • ensure sufficient air circulation in the greenhouse to reduce humidity
  • if tomatoes are covered, they dry faster (moisture reduction)
  • plant in nutrient rich soil to keep immune system strong
  • Maintain a planting distance of at least 40 centimeters from large tomato varieties
  • do not wet the leaves when watering
dried tomatoes on a tomato plant

Didymella fruit and stem rot (Didymella lycopersici)

Didymella lycopersici is one of the tomato diseases caused by a fungal infection. Transmission takes place via the wind and rain. The fungal spores can get inside through wounds and the stalks on the tomatoes.


  • sunken bark tissue on stem just above soil level
  • black colored bark tissue on lower stem
  • in the advanced stage the plant withers
  • Tomatoes develop dark discoloration at the base of the stalk and can begin to mold
  • Leaves are turning increasingly yellow


The tomato plant can be saved from dying by treating it as described under "Earth Blight", as long as the damage is limited. Affected tomatoes can no longer be used and must be disposed of.

Preventive measures:

  • Plant tomatoes sheltered from the wind
  • do not use seeds from infected plants
  • avoid injuries/wounds from sticks and cords
  • Clean plant stakes regularly and replace strings
  • Change crops regularly

Late blight (Phytophthora infestans)

Late blight is one of the fungal diseases with the causative agent Phytophthora infestans. This fungus occurs mainly on potatoes and is carried by the wind on tomatoes. Optimal conditions for rapid spread are temperatures between 18 and 20 degrees Celsius in combination with high humidity. It affects almost only field tomatoes.


  • first symptoms in the form of brown, sunken, hard spots on the fruit
  • initially gray-green spots, which then turn black
  • Moisture favors the formation of grey-white fungus on the undersides of the leaves
  • leaves die off


You should react quickly, because the more this type of fungal disease progresses, the plant and, in the worst case, entire beds die off quickly. If detected early, this egg fungus can be combated with a pesticide such as Atempo® Kupfer-Pilzfrei from Neudorff®, which can also be used on potatoes to prevent the fungus from spreading. Far advanced damage patterns only allow the plant to be disposed of. From the moment the infestation occurs, the tomatoes are no longer suitable for consumption.

Preventive measures:

  • Do not plant/sow tomatoes near new potatoes
  • Do not wet parts of the plant that are above the surface of the soil and keep them dry
  • Choose a location on a warm south side, ideally with wind and rain protection
  • ensure sufficient planting distance of about 50 centimeters (promotes rapid drying)

TIP: If you put a flower pot with a drainage hole in the ground next to the plant, you can use it to water the soil without hitting the leaves or stems with water. Make sure, however, that the edge of the pot is not placed at ground level, so that useful bugs cannot fall in.

Tomato disease on a tomato

parasitic diseases

A balance between plantings and beneficial animals is welcome in tomato planting. They protect against numerous tomato diseases caused by pests. Nevertheless, beneficial insects are not always a guarantee that parasites stay at a safe distance. Many of them cause damaging images, which is why a speedy response is required.

Whitefly (Trialeurodes vaporariorum)

The whitefly belongs to the whitefly family and often causes tomato diseases with extensive plant damage. This pest is mostly found in greenhouses.

Under optimal temperature conditions, the adult animals lay numerous eggs, from which larvae develop, which ultimately grow into whiteflies. Propagation takes about six to seven weeks. Here you should have already spotted the whitefly near your tomatoes beforehand.


  • about two millimeters long insects with a white body
  • are usually on the underside of leaves
  • when shaken, they fly away from the plant
  • often appear in large numbers
  • yellow speckles on the leaves
  • Plant increasingly loses vitality
  • increased leaf drop
  • forms sticky honeydew
  • Honeydew promotes other tomato diseases, such as sooty mold, which causes black spots on the leaves


  • by beneficial insects such as parasitic wasps or ladybirds (available in specialist garden shops)
  • Yellow stickers as an insecticide promise a high level of effectiveness, especially against eggs and larvae
  • spray with soft soap solution: mix 1 tablespoon of soft soap in one liter of water plus 100 milliliters of spirit

TIP: If you pay attention to the suitability for vegetables when buying yellow stickers, you can wash the tomatoes well after treatment and eat them without hesitation. With a soft soap treatment, washing removes any residue that could affect flavor.

Tomato disease on tomatoes

Preventive measures:

  • Ambient temperature should be below 25 degrees Celsius to prevent propagation
  • Set up insect hotel to attract beneficial insects
  • Avoid planting tomatoes near cabbage (whiteflies particularly like cabbage)

spider mites

Spider mites prefer warm, dry climates, although adult specimens easily survive the winter. They damage the plant by depriving the leaves of life energy while sucking food. In the worst case, this can result in the tomatoes dying off. They are usually more common in greenhouses than outdoors.


  • up to a millimeter large, white animals
  • settle predominantly on the undersides of the leaves
  • They spin fine webs on leaves and stems to protect themselves
  • cause the leaves to turn yellow
  • Leaves dry up
Spider mite infestation


Since the biggest enemy of spider mites is moisture, a strong water shower often helps to combat them. A translucent plastic film stretched over it keeps the moisture longer. However, this should not last longer than a day, otherwise the risk of fungal diseases is increased. The wet method should only be used during warm, dry days so that the tomatoes can dry off quickly.

In the case of a heavier infestation, it is advisable to use a neem oil product, which clogs the spider mites' respiratory organs and causes them to die.

Preventive measures:

  • Ensure a balanced humidity ratio in greenhouses
  • keep the soil of the tomatoes evenly moist
  • Regular fertilization and optimal care strengthen the immune system

Other tomato diseases

In order to cause harmful images in tomatoes, tomato diseases caused by fungi, bacteria or pests do not necessarily have to be present. In some cases, these are due to poor conditions and other factors that do not meet the minimum needs of the plants.

spoon leafiness

One of the typical and frequently occurring tomato diseases is leaf curling, which is referred to in botany as spoon leaf. The leaves curl up or down like a spoon. The main cause is usually incorrect care or a suboptimal location.


  • Soil over-fertilized, so that too much nutrients (nitrate)
  • too much pinched (removed new shoots)
  • been too dry for too long
Leaf curls on a tomato plant


The only option here is to create better conditions, adjust the amount of fertilizer as needed, water regularly and be more careful when cutting off new shoots in the future. Once the tomatoes have received enough water and the fertilizer content in the soil has slowly decreased over time, the plants usually recover on their own.

Tomato black inside

If your tomatoes are black on the inside when you cut them open, this is probably due to a lack of calcium. If the soil conditions are optimal, it can still happen that the calcium contained therein is not transported into the interior of the plant. This can be the result of soil that is too compact, for example, which generally promotes tomato diseases. This disrupts the ripening process and the tomatoes turn black on the inside. In addition, the so-called blossom end rot develops increasingly at the base of the flowers.

Tomato diseases, blossom end rot

If you work algae lime into the soil for diseases like this, the soil structure improves and the absorption of nutrients is significantly stimulated, so that calcium can also be absorbed in abundance. Damaged parts of the plant must be cut off.

blossom end rot

Blossom end rot is a special type of tomato disease that shows pictures of black spots forming on the leaves and tomatoes. The visual impression often arises that the tomatoes are rotting.

Blossom end rot is also a result of calcium deficiency, such as that caused by compacted soil and restricted nutrient transport. Excessive humidity and prolonged drought promote progressive damage. Here it is advisable to proceed in the same way as under "Tomatoes are black on the inside" in order to optimize the nutrient transport again. Damaged areas must be removed from the plant. If the tomatoes are affected, they should no longer be eaten.

Tomato diseases, blossom end rot

As a preventative measure, you should occasionally water with hard water, only use organic fertilizers such as compost and measure the pH value so that you can prevent a new calcium deficiency if necessary.

Tomato white inside

Did you harvest nice-colored tomatoes, cut them open and they are white on the inside? Then you will usually not find an answer among the tomato diseases, but that can be due to the ambient temperature being too high. Here botanists speak of "heated" or "cooked".This happens more often when your tomatoes are exposed to the blazing sun or hot midday sun in midsummer. Of course, tomatoes can also turn white inside in a greenhouse that is significantly too warm and spread as one of the most unwelcome diseases. This is usually due to poor climatic conditions in the greenhouse, where there is no air circulation and the hot sun hits the plants unfiltered without additional sun protection.

To prevent this, plant tomatoes in a location where they will not be exposed to hot, direct sunlight. If necessary, sun protection must be installed later. The tomatoes are usually edible. The white spots can only harden at most.

Green or yellow collar diseases

With diseases such as green and yellow collars, there is persistent immaturity no matter how long the tomato is left on the plant.

Green and yellow collar diseases are caused by too much sunlight hitting the plant directly and/or a lack of potassium or too much nitrogen. The latter mainly shows a yellowing of the collar.

Tomato plants in the garden

Clear characteristics are:

  • yellow or green collars
  • all tomatoes are affected
  • a clear difference in ripeness can be seen compared to ripened fruits
  • remain hard in their consistency

Preventive measures:

  • look for an optimal location where no direct sunlight is possible
  • do not use too much or no low-lime irrigation water
  • Choose more suitable tomato varieties if a sunny location cannot be avoided, such as Culina or Vitella
  • do without the "Harzfeuer" variety in a sunny location (it is particularly susceptible to sun-related diseases)
  • set up sun protection if necessary
  • Measure the pH value regularly and fertilize with algae lime if there is a lack of lime or if the soil is acidic
  • do not use nitrogenous fertilizers

Magnesium deficiency diseases

More often, signs of tomato diseases may appear, which are due to a lack of magnesium. Usually this consists of sandy, light and acidic soil.

A magnesium deficiency becomes clear through the following characteristics:

  • brightening in color mainly on the lower and middle leaves
  • yellowing develops between the leaf veins
  • Main leaf veins remain unaffected
  • in the advanced stage the leaves turn brown and dry up
Tomato diseases, yellow leaf discoloration

Cause and treatment:

A magnesium deficiency is usually the result of an imbalanced relationship to potassium and too high a nitrogen content. As a result, the absorption of magnesium by the root is strongly influenced and a deficiency symptom can occur. Nitrogen in particular slows down the supply of nutrients via the roots.

Epsom salt is an effective measure in acidic soils, as is algae lime, which has a high calcium carbonate content and promotes the uptake of nutrients by the tomatoes.

Tomato diseases from cold

If tomatoes are too cold, damage can occur, which can sometimes lead to the suspicion of the worst tomato diseases. In fact, cold is capable of causing a die-off, but with optimal preparation, this is easily preventable.


  • lower leaves turn light between the leaf veins
  • later they turn brown to black and the plant tissue dies (necrosis)
  • leaves dry up
  • the damage moves upwards and gradually causes the plant to die off
Tomato diseases, leaf discoloration


The less frost damage has progressed, the higher the success rate when you cut off affected parts of the plant. At the same time, the plants will regenerate in warmer temperatures, provided they have been well cared for and have a strong immune system and still have sufficient energy. Nutrients also support regeneration.

Preventive measures:

  • avoid temperatures below six degrees Celsius
  • temporarily cover young and potted plants with foil when the temperature is expected to drop
  • ensure a good nutrient content in the soil to prevent deficiency symptoms

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