Main suspects: late blight and brown rot
If brown leaves appear on tomatoes during warm, humid weather, an outbreak of the dreaded latex and brown rot is to be feared. The spores of the pathogen, which multiplies explosively, already call for 10 hours of permanent moisture. Brown spots on foliage and stems are considered the first symptom of the plant disease. Immediately remove all discolored parts of the plant and dispose of them with household waste.
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Since there is currently a lack of effective control agents, prevention is becoming more relevant. Potatoes should never be planted in the immediate vicinity. Basically choose a sunny, air-bathed location. So that the leaves do not become unnecessarily damp, always pour the irrigation water directly at the roots.
Trigger in dry weather
If brown leaves appear on tomatoes in consistently dry weather, this is no reason to give the all-clear. Various other causes come into question, with fatal consequences as well.
- All kinds of pests such as aphids, tomato rust mites or thrips
- Dry spot disease at temperatures above 25 degrees Celsius
- Tomato wilt caused by the bacterium Corynebacterium Michiganense
- Stem and root rot, a common fungal infection following irrigation errors
- Leaf spot disease, also a fungal infection with additional curling leaves
Brown leaves indicate a lack of nutrients
Once diseases and pests have been eliminated from culprits, take a critical look at fertilizing your tomato plants. A lack of certain nutrients can also cause brown leaves:
- A lack of nitrogen causes the leaves to turn brown from the tip
- an undersupply of phosphorus causes the roots to wither and turns the leaves brown
- too little potassium causes brown leaves that spread towards the center
- When there is a shortage of magnesium, the leaves initially turn a light yellow, later a brown color
Tips & Tricks
If you plant your tomatoes under a rain cover, you have the best chance of not being confronted with brown leaves. Your own greenhouse is not absolutely necessary for this. With a little manual skill you can build a rain canopy yourself and improve the mounting conditions many times over.
