Soilborne wheat mosaic (SBWM) was first discovered in the central plains of the USA in 1919. By 1923, Soilborne wheat mosaic virus (SBWMV) was identified as the cause, making it one of the earliest known and first soilborne wheat viruses. here.
SBWM was detected in Washington State for the first time in spring 2008, although it was detected in an adjacent county in Oregon about 1995. It has now been confirmed in three fields, all in the same vicinity near Walla Walla. How widely the disease occurs in Washington is not known.
Usually only autumn-sown wheat develops symptoms, although spring wheat also is susceptible. Symptoms occasionally develop on rye, barley, and other grasses.
Losses in winter wheat to SBWM vary with the variety, virus strain, and environment, but can be substantial when a susceptible variety is grown in a field that is completely infested. Entire fields or areas of fields can be damaged.
Symptoms of SBWM range from mild green to prominent yellow mosaics on the leaves. Symptoms are most prominent on early-spring growth and rarely appear in autumn. As new leaves unfold, they appear mottled and develop dashes and streaks parallel to the veins. Leaf sheaths are also distinctly mottled. Rising temperatures in spring slow and eventually stop disease development.
Stunting can be moderate or severe. Some strains of the virus cause rosetting in highly susceptible cultivars. Fields may be uniformly diseased but more often show a pattern of symptoms that corresponds to distribution of the vector, Polymyxa graminis, which preferentially inhabits low-lying wet areas.