Risk factors

Environmental conditions play an important part in the appearance of the disease. A soil temperature of around 25°C will encourage wilting, whereas very few symptoms will be seen at 16°C.

Survival of the bacterium in a bare soil appears to be low, while haulms and tubers left in the field provide habitats that enable the bacterium to survive for several years in the fields. Cool and moist soils encourage the survival of this bacterium.

Infected tubers are one of the main inoculum sources, as they can carry latent infections for several generations before the amount of bacteria becomes sufficient to produce the characteristic symptoms of the disease (wilt and ring rot). The bacterium may also be disseminated mechanically, through contact of healthy tubers with infected tubers or surfaces having been in contact with the infected tubers (farm equipment, storage facilities, etc.).

Some insects, such as the Colorado potato beetle (Leptinotarsa decemlineata) and the green peach aphid (Myzus persicae), can also carry this bacterium.