Donald M. Ferrin, Hadziabdic, Denita, Hollier, Clayton A., Overstreet, Charles
Black leg is caused by the bacterium, Pectobacterium carotovorum subsp. carotovorum (previously Erwinia carotovora subsp. carotovora). The bacteria enter the tubers through stolons, creating black sunken lesions at the stem end. Note the infected tuber with soft rot in the center. Often secondary bacteria attack already weakened plants, resulting in total plant collapse.
Potato leak (watery wound rot or shell rot) is caused by soil-borne pathogen, Pythium ultimatum. Disease affects only tubers in which dark lesions spread fast, resulting in soft rot and foul odor. A distinct dark brown margin may separate diseased from healthy tissue. As disease progresses, infected tubers become almost black and exude a dark, watery liquid.
Pink rot is caused by soil born pathogen, Phytophthora erythroseptica. When cut and exposed to air, infected tuber tissues change from cream to pink color in period of 20-30 minutes and then progressively darkens to brown and finally black. Color change is good diagnostic tool to distinguish between this disease and potato leak. Disease is favored by cool weather and wet soils.
Root knot nematodes (Meloidogyne spp.) cause the formation of galls on potato roots and tubers. Severely infected plants may turn yellow, resulting in stunting and wilting. Root knot nematodes can cause significant damage to potato production, reduce the quality, yield and marketability of the product.
The LSU AgCenter and the LSU College of Agriculture