M A Y / J U N E 2 0 1 7 POTATO GROWER 21 become tan in color (Figure 7). A pale green to yellow border often surrounds the lesions. Severely infected fields often produce a dis- tinct odor. Late blight infection of tubers is characterized by irregularly shaped, slightly depressed areas of that can vary considerably in color from brown to purplish color of variable size on the skin (Figure 8). These symptoms may be less obvi- ous on russet and red-skinned cul- tivars. A tan to reddish-brown, dry, granular rot is found under the skin in the discolored areas, extending into the tuber usually less than one half inch (Figure 9). The extent of the rotting in a tuber depends on susceptibility of the cultivar, temperature and length of time after the initial infection. The margin of the diseased tissue is not always distinct but can be, particularly in seed potatoes that have been stored at cold storage temperatures (Figure 10). Figure 2. Late blight lesions expand rapidly into large, dark brown or black lesions, often appearing greasy. (Photo credit: Andy Robinson, NDSU/UMN)