Black Point

Kernels are discolored or blackened, usually at the embryo (germ) end. The entire kernel, or just a portion of it, can be discolored. Although black point does not usually reduce yield, it can reduce grade and quality. In the U.S. standards for wheat, blackened kernels are considered damaged, and only 2% total damaged kernels are permitted in wheat graded as U.S. No. 1 and 4% in U.S. 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 affects wheat, barley, and rye. It is caused by several common fungi, which are most troublesome when the relative humidity exceeds 90%. Expanding green kernels are most susceptible, although 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. Factors related to moisture, temperature, and plant growth or senescence trigger the infection that results in symptoms. High humidity or rainfall from anthesis (the period when flowers open) to the soft dough stage, high nitrogen fertility, excessive late-season irrigation, and lodging usually are associated with high levels of the disease.

Cultural Control

Black point can be partially controlled without sacrificing yield or quality by reducing the frequency of irrigation after heading and by reducing nitrogen rates. Because black point can still occur at damaging levels in some seasons when these cultural practices are used, the best option for controlling black point is to also plant black point-resistant cultivars. Current cultivars differ in the level of resistance or tolerance to the disease, although no completely resistant cultivars are available.