Identifying Soilborne Wheat Mosaic Virus

Yellowing of SBWMV.
Yellowing and mosaic of wheat infected by Wheat Soilborne Mosaic Virus.

Contributed by Tim Murray and Cassandra BatesSoilborne wheat mosaic (SBWM) is caused by the Soilborne wheat mosaic virus (SBWMV) and is a relatively new disease in Washington state; however, the virus and disease are not new, having been first described in Illinois in 1919. SBWMV was the first virus known to be soilborne in wheat. It is favored by wet soil conditions and is transmitted by a fungal-like protist called Polymyxa graminis. SBWMV survives only in association with spores of P. graminis and once a field is infested, it will remain infested; as a result, grain yields may be reduced annually.

SBWM is a disease of fall-sown wheat. Symptoms typically appear in the late winter or very early spring when temperatures are cool and often occur in patches in a field. Over time, patches enlarge to the point where the entire field is infested. Infected plants are stunted and the foliage appears mottled with white to dark green streaks that are parallel with the leaf veins – a symptom known as a mosaic. The mosaic can range from a mild green to a more severe yellowing.

As temperatures rise, the mosaic symptoms disappear but the effect of the disease remains and is apparent at harvest with yields reduced up to 75% in infected areas. Because of its preference for wet soil conditions, it is advisable to check symptomatic plants in low spots in the field for yellowing, speckling, or mosaic-like patterns developing. If you suspect SBWMV, the WSU Plant Pest Disease Clinic is able to test for this virus.

Please visit the clinic’s website for more information about sample submission and testing fees.

Fortunately, effective resistance genes are available for SBWMV and planting a resistant variety is the best management practice for this disease. More information about the disease and resistant varieties is available on the WSU Small Grains SBWMV page.

Cassandra Bates.

For questions or comments, contact Cassandra Bates via email at or contact the Plant Pest Diagnostic Clinic directly via email at or phone at 509-335-3292.

Tim Murray.

For questions or comments, contact Tim Murray via email at, via phone at (509) 335-7515, or by following him on Twitter @WSUWheatDoc.