Blossom end rot
Blossom end rot is quite a common problem if you grow your own tomatoes. It's caused exclusively by the lack of biologically-available calcium. With a slight lack of calcium in tomatoes, especially in unstable varieties, fruits with gray or brown tops appear the so-called top rot. A dark spot often spreads to half a tomato. The leaves change visibly and quite rapidly, become wrinkled, and their edges slowly die. Burns may appear on both sides of large old leaves. The chlorides occur between the veins, and the whole plant seems to be covered with rust, and later its organs begin to fall off.