A soilborne disease caused by the water mold Phytophthora nicotianae that rots the stalk base and roots, blackening the stem and wilting the plant. It persists in soil for years and spreads with standing water.
Why it matters
Black shank resistance is a main reason growers abandoned classic Corojo and Criollo for modern hybrids, and it drives crop rotation and drainage practice on every serious farm.
In context
"After two seasons of black shank the farm rotated the field out of tobacco entirely."