Common scab and Netted scab

Streptomyces spp.

Kind of organism : Bacteria

Detection method : Visual, PCR

All diseases & pests

Causal agent(s) and transmission

Common and netted scabs are caused by bacteria of the genus Streptomyces, belonging to the Actinomycetes group (heterotrophic bacteria with a filamentous structure and living in the soil).

Two main types of symptoms may be distinguished: common and netted scab, which, accord- ing to recent scientific findings, are considered as two different diseases with separate causal agents seemingly involved and with different responses to climatic conditions and cultivar susceptibility.

For both types of scab, the soil is the main inoculum source as Streptomyces may persist in the soil on organic matter or on roots or residues of host plants.


Common and netted scab are present wherever the potato is grown. Common scab is a serious issue for fresh ware potato production as it can impair the visual aspect of the tuber.

Symptoms on tubers

The symptoms vary greatly:

In the case of an early attack, the yield may be affected.

Risk factors

With both types of scab, infection is via the lenticels during tuber formation and the disease does not progress further during storage. Generally speaking, common and netted scabs are favoured by light, aerated soils.

The appearance of this disease depends on the cultivar (different levels of susceptibility), on the temperature (optimum temperature 19 to 24°C) and on soil moisture (the disease is favoured by dry, aerobic conditions).

The appearance of this disease depends mainly on the cultivar used as only a few of them are susceptible and most potato cultivars are resistant to netted scab. The disease thrives in a cool temperature (13 to 17°C) and wet soil.


The control of common and netted scab must combine different techniques before or during the crop season:

Before planting:

During the growing season: