One of the most common tomato ailments, Septoria Leaf spot is caused by a fungus which weakens the plant and makes fruit susceptible to sunscald. Symptoms forst appear as small, water-soaked spots. Eventually the lesions overtake the leaf. Small black fruiting structures can be seen at the cneter of the lesion if viewed through a good magnifying glass. Septoria can be effectively controlled using fungicides sch as Chlorothalonil.