Early Blight of Tomato
"Plants infected with early blight develop small black or brown spots, usually about 0.25 to 0.5 inch in diameter, on leaves, stems, and fruit. Leaf spots are leathery and often have a concentric ring pattern. They usually appear on older leaves first. Spots on fruit are sunken, dry, and may also have a concentric pattern; frequently they occur near the calyx end of the fruit."