Egg fungi are responsible for the so-called late blight and brown rot. The species Phytophthora infestans infects various nightshade plants such as the tomato (Solanum lycopersicum) and causes typical symptoms on the parts of the plant.
Typical symptoms
You can recognize the onset of an infection by the blurred spots on leaves and stems. If the fungus spreads unhindered, the entire plant dies. As soon as you discover noticeable discoloration on the fruit, it is no longer edible. Tomato disease is characterized by these phenomena:
- Leaf tips appear brown
- On the underside of the leaf, a light-colored mushroom lawn develops
- withered leaves rot and appear black
- The fruits initially bear green-gray to brown spots
- Rotting sets in until tomatoes fall off
Eliminate plant parts
If the first signs of late blight and brown rot appear, quick action is required. The longer you wait with the measures, the more the fungal spores will spread between the plants. In the event of drought in summer and minor damage, you can stop the disease by taking these measures:
- Cut off infected leaves, shoots and fruits with a sharp knife
- Remove severely affected plants completely
- Do not dispose of plant parts on the compost, as this is where the fungal spores survive
- Dispose of damaged plant material in the residual waste
Administer horsetail extract
Experiments by the State Institute for Agriculture (LfL) have shown that the course of the disease is based on Leaves and shoots after a successful fungal infection through the administration of horsetail extract has weakened. In the early stages, the natural product proves to be an alternative to chemical products. The silica contained in the plant parts has a strengthening effect on the cell tissue. However, complete effectiveness could not be determined, so that you should consider other pesticides as the brown spots continue to spread. How to make a broth from horsetail:
- Fill a large pot with field horsetail
- Pour warm water so that parts of the plant are completely covered
- Let it steep for 24 hours at room temperature
- Bring the stock to the boil and simmer for half an hour
- Mix cooled broth with water in a ratio of 1: 5
- Spray the entire plant for three consecutive days
Note: Fruits from infected plants are usually still edible. Harvest
undamaged tomatoes early and let them ripen on the windowsill.Fight chemically
Apart from horsetail broth, there are no effective ecological means that help against the fungus. Once the disease has broken out, in most cases only chemical treatment will help. Some fungicides are approved for private use in house and allotment gardens. They are available under the names tomato, vegetable or fruit-mushroom-free. It makes sense to use several of these preparations alternately. Otherwise, the fungi quickly develop resistance and continue to spread.
Prevent illness
The most important measure to contain pathogens is to prevent water spray on the leaves. So that no spores from already infected parts of the plant are washed onto healthy leaves and shoots, you should not water the plants from above. Pay attention to good hygiene during care and harvesting measures. Fungal spores often settle on utensils and persist until they reach the appropriate host plants. These recommendations are important:
- Pour just above the substrate
- Snap off leaves close to the ground down to the lowest fruit cluster
- Disinfect spiral sticks, secateurs and knives before use
Planting tomatoes properly
The nightshade plants should be in a location that allows them to dry off quickly after downpours. Waterlogging in the substrate can also promote disease, as the evaporation water creates a moist microclimate. Compacted soils should be loosened beforehand with a plow or sow tooth. The ideal location for Solanum lycopersicum looks like this:
- sunny and sheltered
- ideally under one roof
- well ventilated on all sides
- humus-rich substrate with low proportions of loam and clay
- soil loosened with sand
Keep your distance
Since potatoes are one of the main host plants of the Phytophthora fungus in addition to tomatoes, you should combine them all in one
Put a generous space between them in the bed. As a result, there is no contact and the risk of disease transmission through spores is lower. A minimum distance is also important between the individual tomato plants so that the leaves dry off well. If there is a humid microclimate between the plants, fungal spores can develop better. The distance does not only apply spatially but also temporally, because the crop rotation counteracts the spread of the disease.
How to do it right:
- Plant potatoes at least 50 centimeters away
- Plant tomato plants at a distance of 80 to 100 centimeters
- Plant young plants in a new bed every year
- Do not use aubergine, paprika or physalis growing varieties for tomatoes
Tip: Resistant to disease are native species such as Humboldt tomatoes (Solanum humboldtii) or currant tomatoes (Solanum pimpinellifolium). The varieties 'Phantasia', 'Primavera', 'Philovita' and 'Primabella' are more resistant.
Fertilize in a targeted manner
Pathogens have less chance of infection if the plants are healthy and growing vigorously. The right supply of nutrients supports stable plant tissue so that the fungal spores cannot easily penetrate the cell walls. A sufficient supply of potassium is important for tomatoes in order to prevent brown and late blight. The ideal fertilization provides three nutrients:
- Work compost into the substrate before planting
- give about 50 to 80 grams of organic fertilizer after two months
- Apply some organic tomato fertilizer three to four weeks before harvest
Tip: To make the plants more robust against brown rot and late blight, you should spray the leaves with plant liquor on a weekly basis. Manure made from horsetail, onion peels and garlic have proven successful.
