Blossom end rot
A dark, sunken patch at the base of tomatoes, chillies and other fruit, caused by a shortage of calcium in the developing fruit.
Also known as: BER, Calcium deficiency in fruit
Symptoms and identification
A water-soaked spot appears on the blossom end of the fruit (the end opposite the stalk) and turns into a leathery, sunken, brown or black patch. The rest of the fruit looks normal, and the leaves stay healthy.
Causes
It is not an infection. The plant cannot move enough calcium to fast-growing fruit, usually because of uneven watering, root damage or very high nitrogen feeding, even when the soil contains enough calcium.
Organic treatment
Remove affected fruit so the plant puts energy into healthy ones. Even out the watering; new fruit usually develops normally. A calcium foliar spray can help in the short term.
Prevention
Water deeply and regularly so the soil never swings between dry and soggy, and mulch to keep moisture even. Use large containers, avoid heavy nitrogen feeding, and add crushed eggshells or bone meal at planting on poor soils.
Chemical treatment (use with care)
Not needed. Fungicides and insecticides have no effect on blossom end rot.