The last few summers have been wet and mild which at my allotment site means blight! This mainly affects potatoes and tomatoes and if your growing organically there's not much to be done about it. If you catch it early enough, the diseased parts of the plant can be removed in the hope that the fruit will ripen before it really sets in.
However, word down my allotment in the last few years has been that Magic Mountain is a blight resistant variety of tomato which crops well, the fruit do not split and they have a great sweet taste. What's not to like? I'm going to give them a go this year.