Some tomato cultivars, including 'Oregon Spring', are affected by catfacing regularly. Both catfacing and blossom end rot can leave the cook with some edible bits of the tomato, though they may be small depending on the severity of the problem. But if the disease called 'late blight' occurs, the crop may be totally lost. Late blight is caused by a fungus, Phytophthora infestans , the same disease organism, in fact, that caused the death of entire potato crops in the 19th century, setting off the Irish potato famine. Tomatoes, potatoes, and eggplant are all in the same plant family, the Solanaceous plants.
Late blight can move very rapidly through plantings.
People who wrote on the Irish potato losses often commented that a healthy field on Monday could be totally dead by Friday. It begins with leaf stalks bending, followed by water soaked 'greasy' looking brown to purplish colored spots on the leaves and stems. There may also be a ring of velvety white ring of mold around the spots and a yellow halo as well. The tomato fruit will develop green water soaked spots which rapidly decay, making the fruit useless and inedible. Late blight affects all leaves new and old.