The underlying tissue is dry with a corky texture and a dark-brown color (Figure 9). (Andy Robinson, NDSU/University of Minnesota) Early blight tuber lesions may be circular or irregular in shape and often are accompanied by a large, raised dark-brown border. (Andy Robinson, NDSU/University of Minnesota)įigure 8. Early blight symptoms on infected tubers appear as dark-colored, sunken lesions on the tuber surface. Tuber lesions may be circular or irregular in shape (Figure 8) and can be surrounded by a raised dark-brown border.įigure 7. Symptoms of early blight infection on tubers appear as dark and sunken lesions on the surface (Figure 7). As early blight progresses during the season, numerous lesions may appear on younger leaves in the upper canopy and leaves may drop or dehisce from the stem as infection becomes severe. Premature leaf senescence, reduced yield, and low dry matter content likely will result from severe foliar infection during the tuber bulking stage.įigure 6. Later in the growing season, numerous lesions may appear on the upper leaves, and leaves may drop as the infection becomes more severe (Figure 6). Elongated, brown to black lesions may develop on the stems and petioles of infected plants. (Andy Robinson, NDSU/University of Minnesota)įigure 5. Chlorotic symptoms may develop on infected leaves through time as lesions coalesce and clusters of infection form. (Andy Robinson, NDSU/University of Minnesota)įigure 4. Multiple early blight lesions on the same leaf may coalesce, or grow together. Elongated, brown to black lesions also may develop on stems and petioles of infected plants (Figure 5).įigure 3. As lesions coalesce, chlorosis (yellowing of plant tissue) may be visible due to clusters of infection (Figure 4). Multiple lesions on the same leaf also may coalesce, or grow together, to form one mass (Figure 3). (a Mitch Bauske, NDSU b John Nordgaard, Black Gold Farms)Įarly blight lesions can be diagnosed in the field easily due to the dark concentric rings alternating with bands of light-tan tissue, giving them a distinctive target spot appearance (Figure 1). However, brown spot lesions (b) do not develop dark concentric rings characteristic of early blight infection, and unlike early blight lesions, also may coalesce across large veins. Similar to early blight, brown spot causes small, dark lesions on lower leaves. Initial early blight lesions on older leaf tissue (a) may be confused easily with brown spot lesions, caused by the fungal pathogen Alternaria alternata (b). These first lesions appear about two to three days after infection, with further sporulation on the surface of these lesions occurring three to five days later.įigure 2. Initial lesions on young, fully expanded leaves may be confused with brown spot lesions (Figure 2). Early blight lesions initially appear as small, circular to irregular dark-brown spots on older (lower) leaves. These spots enlarge up to 3/8 inch in diameter and gradually may become angular-shaped.įigure 1. The first symptoms of early blight appear as small, circular or irregular, dark-brown to black spots on the older (lower) leaves (Figure 1). Potato is the primary host, but the disease also can be severe on tomatoes, and occur on other solanaceous plants such as hairy nightshade. The disease first develops on mature and senescing foliage, and early maturing cultivars are the most susceptible. The severity of early blight is dependent upon the frequency of foliar wetness from rain, dew, or irrigation the nutritional status of the foliage and cultivar susceptibility.Īcross the Midwestern U.S., foliar infection is the most problematic phase of the disease, whereas in the western portion of the country, tuber infection can be more damaging. In most production areas, early blight occurs annually to some degree.
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