Potassium deficiency
Symptoms
Potassium is responsible for metabolism in the plant. When deficient — leaves begin to wither, deform, yellow, the stem weakens, fruits fall prematurely. When a young plant is deficient — it grows deformed, the edges of older leaves dry out.
Control and prevention
One of the sources of potassium is wood ash.
Related problems
Similar symptoms might indicate a different cause — compare them.
Phosphorus deficiency or excess
Phosphorus is necessary for cell growth, flower and fruit formation. When deficient — young plant leaves darken, acquire a purple hue; the growth of an older plant stops, the underside of the leaves and veins are purple. In case of excess — fruits become bitter.
Bacterial spot
Manifests as dark spots with a raised center on leaves and stems, later the leaves begin to yellow. Dark, growing spots may appear on the fruits. Cool, humid weather and splashing water droplets allow the disease to spread rapidly.
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.