June 3, 2025, 8:58 am | Read time: 4 minutes
Tomatoes are a wonderful vegetable for hobby gardeners. They are also suitable for beginners, as they can yield a high harvest and allow you to easily observe each growth stage. Unfortunately, tomatoes are also prone to various diseases. myHOMEBOOK explains the best ways to handle these situations.
If you don’t properly care for tomato plants in the garden or keep them in an unsuitable location, you risk diseases. Early signs can include brownish spots, dry areas, or yellowing leaves. However, there are ways to treat these diseases if you recognize them early.
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1. Late Blight
Late blight is one of the most common tomato diseases and can ruin entire harvests. It is favored by too much moisture. Symptoms of the fungal infection include brown spots on the leaves. Just before harvest, the spots also appear on the fruit itself. The tomatoes then become hard and inedible. Affected parts must be removed immediately. In extreme cases, the fungal infestation can lead to the complete death of the plant.
To prevent late blight, ensure that tomato plants do not get wet. They should be covered to protect them from rain and should only be watered from below. Additionally, maintain a sufficient planting distance of about 70 centimeters to ensure the leaves of individual tomato plants do not touch and air circulation is guaranteed.
2. Blossom End Rot
Typical symptoms of blossom end rot are brown to black spots at the bottom of the tomato, around the blossom end. These spread over time and eventually harden. Affected tomatoes are inedible. Contrary to common belief, blossom end rot is not a fungal infection but is caused by calcium deficiency due to drought stress. This deficiency is often caused by improper watering. Even if the soil has enough nutrients, the plant cannot absorb them due to irregular watering cycles.
Preventing this tomato disease is quite simple. Regular watering! Especially in high temperatures, this should be ensured. It is also advisable to remove the leaves below the first fruit cluster to ensure direct nutrient transfer.
3. Early Blight
If round, gray-brown spots appear on the leaves of the tomato plant, a fungus known from potato cultivation has taken hold: Alternaria solani. It prefers warm and humid places and usually first appears on the lower leaves of the tomato plant. These symptoms can spread to higher shoots and also affect the fruits themselves, making them inedible. Therefore, it is advisable to remove affected leaves immediately, but not in the compost.
To prevent early blight, it is recommended to plant tomatoes in a covered location. Since the fungus overwinters in the soil, all lower leaves up to 30 centimeters high can be removed as a precaution.
4. Powdery Mildew
Powdery mildew is a fungal infection that appears as early as spring from the end of May. The leaves of affected tomato plants develop a powdery white coating. As a so-called fair-weather fungus, powdery mildew occurs, especially in warm and dry conditions. Affected plant parts must be removed to prevent further spread of the tomato disease. A mixture of milk (preferably raw milk) and water has proven effective for further control. The two parts should be mixed in a ratio of 1:9 and sprayed on the plants once a week. The microorganisms in the milk combat the fungus and also make the plant more resistant.
Since the fungus prefers warm and humid weather, it is advisable to water in the morning so the plant can dry out during the day. Additionally, tomatoes should be planted at a sufficient distance from each other to allow air circulation.
There are no tomato varieties that are completely resistant to diseases. However, important decisions can be made when choosing varieties. Some types are more resistant and have, therefore, proven themselves in cultivation. Recommended tomato varieties include “Philovita,” “De Berao,” and “Phantasia.”
5. Stem Rot
If dark spots appear on the lower part of the stem, it is usually stem rot, also caused by a fungus. Over time, wilting symptoms appear with this tomato disease; the fruits turn black and begin to dry out. As with similar diseases, affected plant parts should be removed and disposed of, but not in the compost. Often, fungal spores have also settled in the plant stakes and strings. If necessary, the soil should also be replaced. If symptoms appear, they should be removed or cleaned. Since the fungal infection first takes hold on the stem, caution is advised when pruning! Too much injury provides an entry point for the infestation.
To prevent this fungus, ensure that the crop is not planted too deeply. The stems should not remain too moist. It is important to follow crop rotation. It is not advisable to plant tomatoes in the same spot every year. Additionally, make sure to follow proper crop rotation practices.
Did you know? There are also some pests that can make life difficult for tomatoes, such as the tomato hornworm, the vegetable owl, or the tomato russet mite.