County Ag News

Early Blight in Tomatoes and Potatoes


Early blight is a fungal disease that affects both tomatoes and potatoes. Symptoms are leaves that turn brown and drop off of the plant beginning at the bottom of the plant and gradually progressing towards the top of the plant. 

Early blight, caused by the fungus “Alternaria solani,” is a debris-borne pathogen, meaning it overwinters in infected potato and tomato plant parts remaining in fields after harvest. In the spring, spores (conidia) are produced on infected plant debris and dispersed by wind and rain splash and infect first fully expanded leaves near the soil. 

The use of mulch in gardens will greatly reduce infections caused by rain splash. Generally, first foliar lesions are observed in early July and are characterized as dark brown to black and circular with distinctive target patterning within the lesion. Often, lesions are constrained by leaf veins giving the appearance of an angular edge. 

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