First aid for sick tomatoes

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Juicy red tomatoes are the pearls of every vegetable garden. Ripened in the sun and fresh from the shrub, the "paradise apples" simply taste heavenly. All the more annoying, when the fruits that have been harvested suddenly get unsightly stains, the leaves dry up or vermin spread on the plants. To avoid such unpleasant surprises, we introduce you to the most important diseases and pests of tomato plants and explain what you can do about it.

The most important tomato diseases

Cabbage and brown rot

Herb and brown rot on tomatoes

The cabbage and brown rot can destroy whole tomato crops

The cabbage and brown rot is by far the most common tomato disease. The causative agent is a fungus called Phytophthora infestans, which is often kidnapped by infected potato plants on open-air tomatoes. Especially in damp weather, the rot spreads rapidly over the whole plant. This gives rise to gray-green to brown-black spots, which continue to enlarge and cover leaves, stems and fruits. The infected tomato fruits get deep hard spots and can not be eaten anymore. Prevent the rot by placing the tomatoes in a greenhouse or foil tent with plenty of space between plants. A covered space on a sunny balcony or terrace is also suitable. Make sure that the tomato plants are not exposed to the rain without protection and that the leaves can dry quickly if they happen. If the tomatoes are in a mixed vegetable patch, you should keep plenty of distance to the new potatoes when planting. Never pour tomatoes over the leaves! Meanwhile, there are many types of tomatoes that show a good resistance to the cabbage and brown rot, such as 'Phantasia', 'Golden Currant', 'Philovita' or 'De Berao'.

Didymella fruit and stem rot

Another tomato fungus, namely Didymella lycopersici causes the so-called fruit and stem rot. This shows up first at the stem approach of older tomato plants, where just above the ground the bark turns black and sinks. So the water transport is interrupted in the stalk. Slightly later, the fruits begin to wither away from the stem in concentric circles and the leaves turn yellow. By wind and humid weather, the spores of the ascomycete spread over water splashes and infected other tomato plants. Chafe marks caused by tie cords or other injuries are entry ports for the pathogen. Therefore try to avoid injury to the tomato plants by using soft fixing materials and careful treatment. If a tomato is infested with the fungus, it should be removed and the stalk and the supports with methylated spirits disinfected.



Drought on a potato plant

A fungal disease, which manifests itself in dry, very warm weather first on the leaves of the tomato plants, is the D├╝rrfleckenkrankheit, caused by the fungus Alternaria solani. The infected leaves get roundish greyish brown spots. As the fungus passes from the soil to the tomato plant, the lower leaves are first affected by the blight disease, later it spreads to the upper leaves. Finally, the diseased tomato leaves roll in and die completely. Also on the tomato stem are elongated oval brown spots. The fruits become soft and mushy. Because Alternaria solani is often transferred from potatoes to tomatoes, the same precautions apply here as in cabbage and brown rot. The fungus does not affect the entire plant, but migrates from leaf to leaf. Early removal of the diseased leaves can stop the spread. Attention: The tomato mushroom sticks to the plant rods (especially from wood) for a long time. Therefore disinfect the material thoroughly after each season!

Powdery mildew


Powdery mildew shows through white spots on leaves and stems. The disease can not be treated with tomatoes with sprays

Even before the powdery mildew tomato plants are unfortunately not immune. The fungus spores of Oidium neolycopersici cause the typical floury-whitish coating on the tomato leaves and stems. Over time, the leaves wither and fall off. The powdery mildew spreads especially in warm and humid weather and is hard to combat in the hobby garden. Although the fungus does not attack the tomato fruits, the plants often become completely engorged in cases of severe powdery mildew. Immediately remove infected leaves to reduce their spread. Nearly mildew resistant varieties are rare, 'Philovita' and 'Phantasia' are considered relatively resistant.

Pests on tomatoes

In addition to the diverse fungal diseases in which tomatoes can suffer, there are also animal attackers who seriously threaten the tomato crop in case of heavy infestation. In addition to the classic garden pests such as aphids, white fly and nematodes, there are a few that specialize in tomato plants.


Liriomyza bryoniae is the Latin name of the tunnel digger who eats through the inside of the tomato leaves. In German: Tomato miner fly. The fly lays its eggs on and under the leaves. The actual pests are the larvae, because they dig the clearly visible entangled Minierg├Ąnge through the leaf tissue of the tomatoes. With a total development time of 32 days from egg to fly the infestation increases rapidly, especially in the greenhouse. In order to prevent the spread of the tomato fly, infected leaves should be removed immediately. Beneficial organisms such as the parasitic wasp help with natural control.

Tuta absoluta

Grazing of a larva of the tomato miner moth

Significant feeding of a larva of the tomato miner moth

Much like the tomato miner fly, the tomato miner's moth (Tuta absoluta) goes to work. The inconspicuous nocturnal gray-brown butterfly with long, bent back feelers is only about seven millimeters in size and spends his whole life on the tomato plant. The females lay about 250 eggs on leaves, in flowers and on young fruits. The damage to the tomato plant occurs first in the upper part of the young shoots and is easy to recognize. Even the fruits are not safe from the larvae of the leafminer. Often a secondary infection with fungi and bacteria is the result of injured fetal envelopes. Detection and control of the tomato miner moth is by pheromone traps. Beneficial insects such as predatory bugs and parasitic wasps can also be used.

bright-line brown-eye

bright-line brown-eye

Night active pest: The caterpillar of the vegetable owl likes to eat tomato plants

Her name sounds cute, but she is not. The vegetable owl, also called the tomato moth, is an inconspicuous brown moth whose caterpillars are characterized by an enormous appetite for tomatoes and peppers. You can see the four centimeters long caterpillars on their green-brown color with thin yellow stripes on the sides and black warts. The pests, like the adult moth, are nocturnal and feed on tomato leaves and fruits. Insect nets or closed greenhouses protect as a precaution against the moth. In the case of caterpillars, you should collect the larvae as quickly as possible and relocate them to stinging nettles. Pheromone traps and neem-based natural preservatives also help against the vegetable owl.

Tomato rust mite

Tomato rust mite infested fruit

The corked tomato fruits look rusted when attacked by the tomato rust mite

A major tomato pest is the rust mite Aculops lycopersici. Their lifecycle lasts only a week, so the growth rate is enormous. Often the mite passes from potatoes to tomato. Since infestation with the tomato rust mite is only very late in the plants visible, combat is difficult. Signs of rust mite infestation are yellowing of the leaves and browning of the main shoots. The flower stems also change color, young fruits cork up, burst and fall off, the whole plant comes in. The only effective control of tomato rust mite is the disposal of the whole plant.

Physiological damage

When tomato plants show growth problems, it does not always have to be a disease or a pest. Often it is poor culture conditions, adverse weather or an unsuitable location that harm the plant. The following typical clinical pictures are due to environmental influences and bad care.

Blossom end rot

Sign of a calcium deficiency

Large black spots on the tomato underside are clear signs of a calcium deficiency

The final bloom is mainly on the tomato fruits in plants that are cultivated in the bed. Around the flower approach are formed plate brownish-black Faulstellen that spread and harden. The newly expelled leaves are clearly too small and deformed. In the end of the crop is not a fungal attack, but a calcium deficiency. This arises mainly in drought stress. If the plant is not sufficiently poured at high heat, the nutrient salts in the substrate concentrate and the fine roots of the tomato can no longer sufficiently absorb the required calcium in the soil. The prevention of the end of the blight is very simple: Make sure, especially in hot summers for an even water supply and do not let tomato plants wither. In the case of very strong expression, the soil in the garden bed should be improved with carbonated lime or seaweed lime.

Green collar or yellow collar

Yellow collar of tomato fruits

Distinctive yellow collar on tomato fruits

If the tomato fruits are not properly ripened and a green or yellow ring remains around the stem, it may be too hot for the tomatoes.Then the appearance occurs mainly on the outer fruits, which are directly exposed to the sunlight. Too much nitrogen or potassium deficiency can also cause a green collar. The fruits are edible, but not very handsome. To remedy this, you should shade the plants in very exposed locations around lunchtime. Do not fertilize too nitrogen-rich and choose insensitive light fruit varieties like 'Vanessa', 'Picolino', 'Culina' or 'Dolce Vita'.

Bursting fruits

Cracked tomatoes

Annoying when the beautiful red tomato fruits burst just before the harvest

Almost every gardener has experienced that: Shortly before the final ripening of the fruit, the skin bursts in several places and with it the dream of the perfect tomato harvest. Bursted fruit on an otherwise vital plant is not a disease but also the result of an uneven water supply. If the tomatoes are suddenly watered after a dry spell, they literally swell up and eventually burst out of their skin. Again, water the tomatoes evenly. If you want to be on the safe side, you can resort to fixed varieties such as 'Green Zebra', 'Corianne' or 'Picolino'.

spoon leaves

If the leaves of the tomato roll up like a spoon, that is a sign of over-fertilization. The phenomenon is also referred to as leaf rolls. Too much nutrient supply or drought stress is usually the trigger and can be easily remedied by a uniform irrigation and slow-acting organic fertilizer.

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