Worldwide distribution. On tomato, although eggplant, capsicum and watermelon are also affected. An important physiological problem.
It is not a disease. Occurs when fruits are green, and a third to half full size.
Light brown areas at the blossom end, becoming dark brown, dry, sunken. More common on first fruit.
Cause: too little calcium (Ca) in e.g., sandy soil; too little or too much water; low pH prevents Ca uptake; conditions too hot and dry; too much nitrogen in the soil.
Cultural control: ensure good drainage (raise beds); add organic matter; apply mulch; do not damage roots when cultivating; use windbreaks; do not use urea, ammonium types of fertilizer or 'raw' chicken manure; tolerant varieties.