Septoria Leaf Spot
Wet conditions favor the development of fungal blights of tomato. Two common foliage diseases of tomato are early blight, caused by Alternaria solani, and Septoria blight, caused by Septoria lycopersici. Both blights attack foliage, particularly older (lower) leaves. Early blight causes brown spots of varying size (up to more than 1/2" in diameter) that typically contain concentric rings of darker brown. Septoria blight causes numerous small ( about 1/8" to 1/4" in diameter) brown spots that develop light tan to white center as they age. The overall effect of both blights is similar. Leaves turn yellow, brown, then wither and die. Septoria blight and early blight both overwinter on infected debris from previous years. If there are only a few plants in a garden, the progress of the blights may be slowed somewhat by removing infected leaves as they appear. Nevertheless, fungicide sprays are likely to be needed if these diseases are present. Many products are labeled, including Bravo and Dyrene, and should be applied every week to 10 days through harvest. Cultural techniques can help to reduce the risk of foliar blight outbreaks, but it takes some advanced planning. At the end of the season, remove as much tomato plant debris as possible from the planting. Till thoroughly in the fall in order to break up remaining infected debris. Rotation away from tomatoes and potatoes for 3 to 4 years also helps to break the debris link in the disease cycle. If a long rotation is not feasible, a 2-4" layer of organic mulch (leaves, grass clippings, straw, etc.) placed over the soil surface after transplanting acts as a barrier against release of fungal spores.