Blossom end rot of tomato has been showing up in some protected growing structures. This article reviews the disorder and summarizes preventive practices.
Blossom end rot is a physiological disorder caused by a deficient supply of calcium to the developing fruit. It is a common problem on tomatoes, but can also occur on peppers, eggplants, and melons. Blossom end rot appears first as a small darkened or water soaked area, usually at the blossom end of the fruit. This spot darkens, enlarges and dries out as fruit matures. The area may be invaded by secondary decay causing organisms. Prevention is the best way to avoid losses from blossom end rot. Prevention strategies emphasize ensuring adequate supply and availability of calcium, and managing plant growth environmental conditions to promote movement of calcium to the developing fruit.
If I could offer just one suggestion it would be to maintain a consistent water supply. In many cases I have seen, this is a key factor. Any interruption of water supply to the roots, for example during hot dry weather, can cause a temporary calcium deficiency in the developing fruit that will lead to blossom end rot. A sudden change to hot sunny weather after a period of cloudiness may promote blossom end rot due to the increase in water demand. In protected culture increasing humidity may reduce blossom end rot because the plant demand for water will be reduced.
Nutrient management is also important. Check that soil calcium levels are sufficient, and in cultural systems where most calcium is supplied through fertigation, assure that sufficient amounts are being applied. Frequently, calcium levels are sufficient and it is getting the calcium to the developing fruit that is the problem. Avoid excess nitrogen. Nitrogen promotes vegetative growth that can compete with the developing fruit for an adequate supply of calcium, leading to blossom end rot. Avoid excess potassium or magnesium because they can interfere with uptake of calcium. High EC in a soilless culture system can also promote blossom end rot.
In addition to managing nutrients and water, providing conditions for a healthy root system is important. Avoid compaction and provide good drainage.
Varieties differ in susceptibility to blossom end rot. Plum types are often more prone to the disorder; it is virtually unknown in cherry tomatoes.
Blossom end rot can cause significant losses and is a problem that can be avoided with proper management. It may take some investigation to determine what measures will be effective in a particular situation; time well spent if it reduces the loss of marketable fruit.