Spraing is an important disease of potatoes. Appearing as internal arcs and spots on tubers, but also sometimes as external rings, this disease seriously affects the quality of potato crops and can often lead to entire stocks being rejected. The disease can be caused by two different viruses: by Tobacco rattle virus (TRV) or Potato mop-top virus (PMTV). Both viruses are soil borne, TRV being nematode transmitted and PMTV transmitted by powdery scab (Spongospora subterranea). Testing of the soil by bait test followed by TaqMan for TRV and/or PMTV, enables growers to make decisions before planting.