Question: What makes the skins on my harvested potatoes scabby?

Answer: Common scab is caused by a naturally-occuring soil microbe called Streptomyces scabies. The optimum pH for scab development is from pH 6.0 to 7.5, so you can reduce scab problems by acidifying the soil to a pH of 5.5. Scab is also more prevalent on sandy or gravelly soils, so increasing soil organic matter can help. If you choose to use manure to enrich soil, use aged manure or apply fresh manure at the end of the season. You can also try planting scab-resistant potato varieties.