Early blight is a common tomato disease caused by the fungus Alternaria solani. It can affect almost all parts of the tomato plants, including the leaves, stems and fruits. The plants may not die, but they will be weakened and will set fewer tomatoes than normal. Early blight generally attacks older plants, but it can also occur on seedlings. Stressed plants or plants in poor health are especially susceptible. Early blight is also a problem with potatoes.
Early blight is a difficult enough disease to deal with, but don't confuse it with the much more problematic late blight that can quickly kill tomato plants and spread for miles.
What Causes Early Blight
The early blight fungus can come from many sources. It can be in the soil, it can already be on seeds or seedlings you purchase, it can over-winter in the diseased debris of your tomato plants and it can persist in the soil or debris for at least 1 year. Although early blight can occur in any type of weather, it favors damp conditions, like frequent rain or even heavy dews.
Keep reading for more photos and descriptions of early blight's symptoms.