Pathogen. The early blight fungus is found in most soils where potatoes are grown, and the disease develops every season. The fungus overwinters in the soil on dead leaves, vines or infected tubers.
Disease development. In the spring, the fungus produces spores on the infected crop residue. Spores are spread to healthy plants by wind and rain. Usually, older leaves close to the ground are infected first. Early blight is more severe as the potato crop ages or if the crop has been stressed by poor nutrition, drought, hail, insect damage or other stress. Plants infected with Verticillium or expressing common mosaic symptoms are particularly
susceptible to early blight.
If early blight is severe, lesions may also be found on stems and tubers. Tuber infection occurs at harvest primarily through cuts, bruises or wounds. The variety Nordonna is susceptible to tuber infection.
concentric rings that resemble a target board
occur on the leaves Dead tissue usually
collapses leaving a hole
by large leaf veins and surrounded by
a yellowish area
Early blight lesions are not limited by small leaf
veins
infection is severe
slightly sunken and round to irregular in shape
The lesions are often surrounded by a raised
violet blue border
brown dry and corky If the infection is shallow
the rotten tissue can be easily removed Tuber
symptoms appear in storage
