Black Point of Wheat

Kernels are discolored or blackened, usually at the embryo (germ) end. The entire kernel, or just a portion of it, can be discolored. Although usually not yield-reducing, black point can reduce grade and quality. In U.S. wheat standards, blackened kernels are considered damaged, and only 2% are permitted in wheat graded as US No.1, and 4% in US No.2. Black point is especially important on durum wheat because black specks can appear in the semolina, making it undesirable for further processing.

Black point is a disease that affects wheat and barley; it is most important on durum wheat. It is caused by several common fungi. These fungi are most troublesome when the relative humidity exceeds 90%. Expanding green kernels are most susceptible, while premature seed senescence also promotes black point. The fungi that cause black point often occur on kernels that do not show symptoms of black point. Some factor(s) related to moisture, temperature, and plant growth or senescence triggers the infection that results in symptom expression. High humidity or rainfall from anthesis to soft dough, high nitrogen fertility, excessive late season irrigation, and lodging usually are associated with high levels of the disease.

Black point can be partially controlled by reducing irrigation frequency after heading and by reducing nitrogen rates, without sacrificing either yield or quality. Because black point can occur at damaging levels in some seasons despite modifications in cultural practices, the best option for control is to combine reduced input practices with black point resistant cultivars. Current cultivars differ in the level of resistance or tolerance to the disease, although there are no completely resistant cultivars available.