Prevent and treat tomato diseases

Blotchy leaves, wilted foliage, mushy or even moldy fruit: there are several tomato diseases that can ruin a delicious harvest. Solanaceous plants are susceptible to many fungal diseases. We explain how you can recognize it and what you can do against it.


Late blight is one of the most common diseases of tomatoes. Characteristic are gray-green to brown spots on leaves, but also on stems and shoots. The fruits may also be affected. They get hard, gray-green to brown spots and often start to rot.

Late blight is caused by the fungus Phytophthora infestans, which also affects potatoes. The disease spreads in humid, rather cool summers and high humidity. Therefore, protect tomatoes from rain with a roof. Do not water over the leaves. Tomatoes that are too close together and in close proximity to potatoes can also promote late blight. Therefore you should keep the plants at a distance. You can also remove the lower leaves of tomatoes so that the plant is better ventilated. You can strengthen it additionally with a broth of field horsetail. Check the leaves regularly and remove the diseased parts of the plant immediately, as the disease spreads quickly. You can no longer eat the infested fruits. Do not dispose of fruits and plant parts on the compost, but in the garbage.

Powdery mildew

Powdery mildew is divided into powdery mildew and downy mildew. In both cases, a white, floury coating forms on leaves and stems. In the case of powdery mildew, the tops of the leaves are affected. It is easy to wipe off. In the case of downy mildew, the coating appears stubbornly on the undersides of the leaves. The effect is the same: the leaf wilts, in the long term the plant withers and dies. Powdery mildew usually occurs in warm, dry summers, downy mildew in cooler, moist conditions. To prevent powdery mildew, you should always plant tomatoes in an airy and sunny location with sufficient distance between them and do not fertilize them excessively with nitrogen. In addition, you can spray the leaves with a broth of field horsetail. If your tomatoes have powdery mildew, you must remove the affected plant parts immediately and dispose of them in the trash to prevent the disease from spreading. The fruits are usually considered edible. But you should wash it thoroughly beforehand.

Gray mold

Gray mold is widespread in the garden. It can be recognized by a gray-green, velvety turf of mold that covers leaves, stems and fruit.Gray mold is caused by a fungus called botrytis. In humid weather, it mainly attacks stressed and weak tomatoes. To prevent it, a dry, well-ventilated place and sufficient distance between plants is essential. If a tomato plant is infested, you must immediately and completely remove all affected plant parts and fruits and dispose of them in the trash. Velvet spot disease is manifested by yellow spots on the top of the leaves. A velvety gray-brown coating on the underside of the leaves. It is caused by the fungus Cladosporium fulvum and occurs mainly in greenhouses where there is high humidity. Air your greenhouse regularly. Do not plant tomatoes too close together. You should completely remove diseased plants and dispose of them in the garbage – as well as the soil, because the fungus can survive in the soil.

Fruit and stem rot

In fruit and stem rot, the stem darkens just above the ground, and the affected areas sink in. In addition, the leaves can wilt and turn yellow. Fruit and stem rot occurs mainly in greenhouse cultivation. It is caused by the fungus Didymella lycopersici. It spreads over the wind. Infects other tomatoes via wounds on the stem. Therefore, make sure that you do not injure the plants when tying them up and that the fastening does not chafe them. If tomato plants are infested, you must remove them quickly and completely and dispose of them in the trash – as well as the soil. In addition, you should disinfect the tomato stick and replace the strings.

Drought spot disease

You can recognize the drought spot disease by roundish, gray-brown, dried spots on the leaves. It spreads leaf by leaf from bottom to top. Stems and fruits may also be affected: The spots are more elongated, the tomatoes rotten.

The drought spot disease occurs mainly in the cultivation in the greenhouse. It is caused by the fungus Alternaria solani, which is also transmitted by wind from potatoes. Therefore, do not plant the two nightshade plants in the immediate vicinity and keep them rather dry.If you catch the disease early, you can prevent it from spreading by removing the affected leaves and disposing of them in the trash. Thoroughly disinfect the tomato stick. The fungus can also survive in the soil.

Cork root disease

You water your tomato plant sufficiently and yet, for no apparent reason, it stops growing, wilts, and sheds blossoms and fruit? Then it could have the cork root disease. This thickens the roots and covers them with a corky layer, so that the plant can no longer absorb water, or hardly at all.

Responsible for this is a fungus called Pyrenochaeta lycopersici. Cork root disease occurs mainly in hot summers in greenhouse tomatoes and can also affect peppers and cucumbers. To prevent the disease, you can graft the young plants. Diseased tomatoes must be dug up immediately together with the root ball and disposed of in the garbage. If the infestation is more severe, you may also have to change the soil, as the spores can survive in the soil.

Tomato wilt

In tomato wilt, the plant withers from the bottom up, first the leaves, then the shoots. The fruits get rough, brown spots. Tomato wilt is caused by the fungus Fusarium oxysporum. This is why it is also known as Fusarium wilt. Depending on the fungus, it also affects peppers, cucumbers, beans and peas. Tomato wilt occurs in greenhouses because the warm climate favors the fungus. To prevent the disease, you can graft the young plants and spread lime on the soil. To prevent the disease from spreading further, remove diseased plants immediately and dispose of them in the trash. The soil fungus can survive in the soil for several years. We therefore recommend to disinfect the site thoroughly or to remove the soil.

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