Why Do My Beetroot Have Rough Corky Patches on the Skin?

Rough, raised, corky, or pitted patches on the outer skin of beetroot — ranging from small surface blemishes to large, irregular, scab-like growths covering significant areas of the root — are caused by the bacterium Streptomyces scabies (common scab) or related Streptomyces species. This is the same pathogen that causes common scab on potatoes. The bacteria are present in most garden soils but cause significant damage only under specific conditions: alkaline soil pH, dry soil during the root development period, and insufficient organic matter. The roots are still fully edible once the scabby areas are peeled away.

How scab develops

Streptomyces bacteria are soil-dwelling actinobacteria that are activated by specific conditions: soil pH above 7.0, dry soil at the surface during the period when the young root skin is forming and vulnerable (roughly the first four to six weeks after roots begin to swell), and low organic matter content. At pH above 7.5 and in dry soil, the bacteria infect the root surface through lenticels and small cracks, producing the characteristic corky overgrowths as the root responds to the infection. At pH below 7.0 and in consistently moist soil, the same bacteria cause much less damage.

How to reduce scab

Do not lime the beetroot bed — beetroot tolerates soil pH as low as 6.0 and the ideal range is 6.5–7.0, which is lower than the pH that strongly favours scab. Maintain consistent soil moisture during the growing season, particularly during July and August when roots are rapidly developing. Watering during this period does more to prevent scab than almost any other intervention. Incorporate organic matter — compost, leaf mould — before sowing to improve moisture retention and lower the pH slightly in alkaline soils.

Are scabby beetroot edible?

Yes, entirely. Common scab is a surface disease — it does not penetrate into the root tissue beyond the outer skin. Peel the root thoroughly (remove more peel than usual to get past the scab layer) and the flesh inside is perfectly healthy and normal in colour, flavour, and texture. Scabby roots store adequately but may deteriorate faster through the scab lesions in wet storage conditions — use them before storing if scab is severe.