Blossom-end rot (BER) is generally thought to be triggered by a localized calcium deficiency in the blossom end of the fruit. It often occurs when dry soil conditions reduce the amount of water movement into the plant, interrupting the movement of calcium to the fruit. Calcium is an important component of cell development. Therefore BER is caused primarily by dry soil conditions, not by a deficiency of calcium in the soil or plant.
A small water-soaked or light brown area appears around the blossom-end of the fruit when the fruit is green or ripening. The lesion darkens and enlarges rapidly, becoming sunken and black. It may affect over half of the fruit. Other organisms may invade the lesion.
Soil or foliar applied calcium has not been shown to be effective in preventing BER. Foliar-applied calcium is taken up and fixed in the leaves, and very little reaches the fruit.
Besides moisture, many other factors seem to influence BER as well. In fact, there is now some thought among scientists that low calcium levels in the fruit are not the trigger for blossom-end rot at all.
The list of factors that may influence blossom-end rot is a long one:
- stress factors, such as dry conditions, that reduce fruit growth;
- high temperatures and intense sunlight, especially following cooler, overcast weather;
- high ammonium-nitrogen levels in the soil,
- high salinity;
- susceptible varieties;
- stress occurring during periods of rapid fruit growth;
- potassium/calcium ratios in the fruit;
- high nitrogen fertilization;
- fluctuations in levels of various growth hormones in the plant.
There is now speculation that stress-free, rapid growth conditions create the susceptibility for blossom-end rot in fruit at a certain stage of development. If conditions suddenly turn stressful, reducing growth rates, blossom-end rot is thought likely to develop. Unfortunately, this does not provide us with a recipe for preventing the problem, so researchers continue to study the disorder.
Avoid deep cultivation, which can prune roots and reduce water uptake. Properly scheduled irrigation will ensure steady movement of water and calcium into the plant. Varieties vary in susceptibility to BER.