Stinking smut

Symptoms

The symptoms of stinking smut or common bunt are not as apparent as those of loose smut. Although stinking smut is not easily identified until the time the wheat heads, infected plants may be slightly to severely stunted. Smut-infected heads have a bluish-green cast, in contrast to the green color of healthy heads. At maturity, diseased heads appear to be plumper than normal heads because of the wide-spreading open chaff (Figure 1). Infected plants are also more susceptible to certain other diseases and to winter injury. The root systems of infected plants are usually poorly developed.

During the development of the head, the kernel is replaced by a smut ball that is a dull, gray-brown color, short, and plump. The smut ball consists of a mass of oily, foul-smelling, dark-brown spores. Smut balls look much like normal kernels, but can be easily crushed (Figure 2). Smutted heads generally stand more erect and remain green for a longer time than healthy heads. Dark clouds of spores are released by the action of a combine in severely diseased fields.

Stinking smut differs from loose smut in that only the kernel tissues within the pericarp are replaced by smut spores, rather than the whole head. Bunted plants are weaker than normal ones, and are often more susceptible to seedling blights and winter injury.