DiseaseOther
Potassium deficiency
Older leaves develop yellow and then brown, scorched edges, and fruit is small and poorly coloured.
Also known as: Potash deficiency, Leaf margin scorch
Symptoms and identification
The edges and tips of older leaves turn yellow, then brown and crisp, while the centre stays green. Fruit ripens unevenly, flowering is poor, and stems are weak.
Causes
Sandy soils, heavy rain and frequent watering wash potassium out. Heavy-cropping plants such as tomatoes, bananas and gourds use a lot of it.
Organic treatment
Apply wood ash (a handful per plant), banana peel compost or seaweed fertilizer, and water it in.
Prevention
Add compost and wood ash or a potassium-rich fertilizer when plants start to flower and fruit.
Chemical treatment (use with care)
Use sulphate of potash at the label rate.