Worst tomato ?

[modeller]

This year I have grown 6 different types of tomatoes and have found considerable differences in the results.

However the one which is the worst is the plum tomato:
San Marzano Astro F1 . The tomatoes are a funny shape like slightly flattened plums with knobs on the bottom and so far I've lost more than half through blossom rot, something they are not supposed to suffer from , because they have a low water content and are mainly for cooking.
This blossom rot occurs even on tomatoes that are fairly big .

[Clanad]

You must have had an extended period of rain or high humidity or at least uneven watering conditions, which, here in the U.S. is a major contributor to blossom end rot. Or, alternatively, you may have planted the tomatoes when the soil had not thoughly warmed in the spring. My organic grower friends say that's often the problem.
I've found a couple of products that are unusually helpful if applied at the first sign of the malady... both are calcium based spray bottles and if one is persitent even some visibly affected fruits can be salvaged. My favorite is made by Safer Company... at least here.
I raise a plant or two of the plum tomatos just because they are so good in tomato based sauces... they even can up for home storage quite well because of the high acidity.

[modeller]

Thanks Clanad but my tomatoes are all in a greenhouse and they are all treated the same for watering and feeding. It is true we have had a most variable summer from temperatures in the 80s in the spring with high humidity to quite chilly periods, 50/60s , during the past month and the night temperatures have dropped even more, but as I said it is only the plum one which is affected. I use a moisture probe which gives me a reading of all the grow bags's moisture content which I try to keep fairly constant.