Damping-off
Agent: Pythium, Rhizoctonia
Symptoms
More of a symptom than a disease. Affects only young seedlings: the stem browns and narrows at the roots, the seedling topples over.
Control and prevention
Use sterile substrate for sowing, ventilate seedlings well, seeds can be soaked in fungicides.
Related problems
Similar symptoms might indicate a different cause — compare them.
Early blight and black fruit rot
Alternaria solani
Usually appears when fruits begin to set. First affects the lower leaves, then the stem and fruits. Large brown or black spots with concentric rings appear on them. Around the spot, the leaf begins to yellow and dies. It also attacks potatoes and eggplants. The fungus is resistant and persists for several years.
Root Rot
Fusarium oxysporum
Common in tomato gardens. Thrives in warm, acidic soils. Infects the plant through the roots, spreads through the circulatory system. The first symptom is yellowing of the lower leaves; dark brown spots are found when the stem is cut. Can affect potatoes, peppers, eggplants.
Mold
Symptoms caused by various fungi. Mold only survives in high humidity.