These diseases are caused by soil-borne fungi and can remain in the soil for several years. General symptoms are yellowing of lower leaves that progresses up the plant, rapid wilting, and premature death. The fungi invade the vascular system of the plant and clog the conductive tissue, thereby interfering with the transport of water. Early blight appears as circular spots with concentric, bull's-eye rings, usually on the lower leaves. Late blight occurs mainly during cool, wet weather.
Infection appears as large irregular spots, eventually turning brown or black.
The under surface of infected leaves often has a white fungal mass. John C. Nye, Dean and Director. Distributed in furtherance of Acts of Congress of May 8 and June 30, 1914. It is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, color, sex, disability, age, or national origin.