Cabbage and brown rot

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When the temperatures rise in the summer, the hobby gardener is happy: For then the tomato plants show their yellow flowers and the thought of a rich harvest gives rise to anticipation. Often, however, a fungus thwarts the tomato buddy. If it rains frequently, it leads to constantly moist tomato leaves. The experienced tomato and potato gardener should now be aware of the danger threatens: the cabbage and brown rot, caused by a fungus called Phytophthora infestans. This fungal disease occurs most often on free-range tomatoes, but occasionally also in cultivation in the greenhouse.

Cabbage blight Brown blight

Cabbage and brown rot on still unripe tomatoes

Crop of herb and brown rot on tomatoes

The first infections of the tomatoes are caused in the spring by diseased potatoes whose released spores are spread by the wind or raindrops. Under humid conditions, zooplasms sprouting from the spores land on the leaves and germinate on tomato leaves. Lower sheets are infested first. While olive-brownish spots form on the upper side, spores appear on the underside in a whitish lawn. Later, the leaves turn black and die. Diseased stems have dark longitudinal stripes that can span the whole shoot. In summer, the fruits are attacked. The tomatoes then turn brown, hard and inedible. The fungus forms mobile spores, which are spread with drops of water and re-infect leaves.
Tip: Always protect tomato plants from moisture and plant sturdy varieties such as 'De Berao', 'Primavera' or 'Primabella'.

Crop of herb and brown rot on tomatoes

Crop of herb and brown rot on tomatoes

Spread of the mushroom

The spores of this fungus (they are used for propagation and distribution) overwinter in seed potatoes. In May / June they are then spread by wind to other potato (Solanum tuberosum) and tomato plants (Solanum lycopersicum). The spores germinate with persistent leaf wetness and infect first the leaves, later also stalks and fruits.


Typical symptoms of herbaceous and brown rot on tomato plants are blurred at the onset of attack, brownish spots on the leaves and stems. In strong moisture forms on the underside of the leaf in addition a delicate, white mushroom turf. Later, the leaves turn black and wither. The upper parts of the affected shoots die. Pale brown spots are also visible on the upper half of the fruit.

Herb rot brown rot tomato

Tomato plant infected with cabbage and brown rot (Phytophthora infestans)


Keep tomatoes protected and sunny so that the leaves can dry quickly after a rainstorm. It makes sense to set up a roof over the plants, which allows good ventilation from all sides. If you want to grow the tomato plants in the bed, make sure you have a loose soil without waterlogging, garden soil is best suited with plenty of humus and little clay and clay content. The soil should be loosened deep with a sow tooth before.
Plant tomatoes and potatoes each year in a different location in the garden and disassemble them as far as possible, as both are among the main host plants of the Phytophthora mushroom. The distance between the individual tomato plants should be between 50 and 70 centimeters, so that they can not touch and infect each other. Single rows are recommended. Only plant small neighboring plants next to the tomatoes so that the tomato leaves are not shielded by the wind.
Pour the plants close to the ground with a soft jet of water and avoid splashing water on the leaves. Remove the oldest ground-level leaves to the lowest fruit level.
Affected leaves and fruits must be immediately unplugged and destroyed. Under no circumstances should the infected parts of the plant be left on the compost, as the spores are very robust and long-lived. Important is good hygiene. Disinfect any objects that come into contact with the tomato plants - such as spiral rods, knives or secateurs. For disinfecting boiling water or a gas burner are suitable.
For each federal state there are phytosanitary warning services, by which one can inquire by telephone after acute danger of infection in the environment.

tomatoes roof

Good protection against the tomato mushroom: a protective roof against moisture

Resistant tomato varieties

Really resistant tomato varieties do not exist, even if some denominations promise that. However, some breeds show a certain tolerance, which delays an outbreak of the fungal disease, such as the varieties 'De Berao', 'Phantasia' and 'Philovita'.


If infestation is present, you can use the following anti-fungal agents (fungicides) in the house and allotments: Tomato-Mushroom-Free Cueva, Vegetable-Mushroom-Free Polyram, Fruit-Fungus-Free Teldor (only in the greenhouse) or Special-Mushroom-Free Aliette. To combat fungus, it is generally useful to use several preparations alternately, as the pathogens otherwise easily build up resistance.

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