By William Terry Kelley
University of Georgia
You've been the victim of blossom end rot on tomatoes. And while it happens to some degree almost every year, the extended drought and now hot weather complete a recipe for an avalanche of blossom end rot this summer.
Blossom end rot is a calcium deficiency in the fruit. There's usually plenty of calcium in the soil. A tissue analysis would probably show that there's ample calcium in the leaves, too.
The lack of calcium that causes BER is actually in the fruit itself. And by the time you see it on the tomato, it's too late to do anything for it. What's even worse is that it's also hard to correct the problem on the developing fruit, too.
Tomatoes are predisposed to BER very early in their development. When they're hardly visible, they have a critical need for calcium. If the calcium doesn't get to the fruit at that critical stage, the die has been cast for BER.
Calcium is an immobile element in plants. Once it becomes part of the leaves or stems, it isn't going to move to newly developing parts of the plant, such as the fruit.
As it takes up water, the plant takes up calcium from the soil. Under hot, dry conditions, the plant is taking up great amounts of water, which is quickly transpired through the leaves to keep the plant alive.
The plant is acting almost like a chimney as it sucks water from the soil and moves it through the plant and out through pore-like structures in the leaves. Unfortunately, this doesn't allow for a lot of lateral flow of calcium to the developing fruit. And they can become deficient.
So, what can you do?
Sometimes there isn't much that will actually help. The biggest factor is moisture. It's hard to keep the soil moist when it's this hot and this dry. And too much water can be just as bad for BER as too little.
A consistent supply of moisture is the best course of action. Avoid cycles of very wet followed by excessive drying. This will help keep calcium flowing into the plant.
Many people try foliar calcium sprays to help reduce blossom end rot. But there's little evidence that these applications help.
Some people add gypsum to the soil at the start of the season, too, to make sure there's enough calcium. This, along with maintaining the proper soil pH, can ensure that calcium is in the soil, but the problem remains getting it to the fruit.
BER is very hard to control and very frustrating if you get it. In some years, you almost just have to live with it and hope you'll get enough good fruit to make it worth it.
(Terry Kelley is a former University of Georgia Cooperative Extension horticulturist with the UGA College of Agricultural and Environmental Sciences.)