Review of liming, pH and common scab risk in potatoes

Common scab of potatoes is a blemish disease caused mainly by Streptomyces scabiei. Current nutrient management guidance for managing the risk of common scab identifies soil acidity as a risk factor for S. scabiei, and in the Nutrient Management Guide (RB209) – Section 5 Potatoes, the guidance is that liming immediately before planting potatoes should be avoided unless the soil pH is very low. The review examined the historic basis of these recommendations and reviewed the most recent studies around the relationship between common scab, pH, liming and calcium in potatoes.

Key findings

Calcium does not appear to be a key causal factor for common scab. Soil pH can continue to be used to control common scab, though it is an incomplete and variable control. The central range for the UK scab causing organisms was pH 4.0 - 7.5. There was limited evidence to endorse liming above the scab organisms tolerance range i.e. 7.5. Liming has soil conditioning and possible yield benefits.

Recommendations

The review identified several area where knowledge gaps exist and where future research could provide further clarity. The current guidance may need to be modified for high pH soils where brassicas and sugar beet are grown. It may be financially beneficial to apply lime if growing a scab susceptible variety such as Maris Piper and soil pH is raised beyond 7.5.