Common potato scab

Common potato scab is a widespread soil-borne disease caused by actinomycetes of the genus Streptomyces, primarily Streptomyces scabies. This pathogen thrives in the soil and attacks the tubers, roots, and stolons, leading to significant cosmetic damage and economic losses, although the tubers remain edible.

The disease affects a wide range of root and tuber crops, including potatoes, sugar beets, carrots, and radishes. The bacteria are persistent in the soil and can survive for many years, spreading through infected seed potatoes, contaminated soil movement, or the application of untreated manure.

Symptoms are characterized by surface lesions on the tuber skin, which can vary from shallow, corky scabs to deep, pitted craters. These lesions may coalesce, covering a large portion of the tuber's surface. While internal tissue usually remains healthy, the exterior damage makes the potatoes unmarketable and susceptible to other storage rot infections.

Development of common scab is highly dependent on environmental factors, particularly soil pH and moisture. The disease is most severe in alkaline soils (pH above 6.0) and during periods of warm, dry weather when the tubers are initially forming. High aeration in sandy soils also promotes the rapid growth of the causative bacteria.

To manage and prevent common scab, farmers should follow these best practices:

• Select scab-resistant potato varieties for planting.
• Practice crop rotation with non-host crops and acidifying cover crops.
• Ensure adequate soil moisture during the critical tuber initiation stage.
• Avoid over-liming the soil and the application of fresh, uncomposted manure shortly before planting.