Common scab

Common scab is a significant plant disease caused by actinomycetes from the Streptomycetaceae family, most notably Streptomyces scabies. These bacteria are ubiquitous in the soil and act as opportunistic pathogens that target the underground parts of various economic crops.

The disease primarily affects potatoes, sugar beets, carrots, radishes, and parsnips. While it does not typically kill the plant, it causes severe economic losses by compromising the aesthetic value of the tubers and roots, making them unmarketable and susceptible to storage rots.

Symptoms are characterized by surface lesions, corky scabs, or deep pits on the skin of tubers and root vegetables. These lesions vary in size and appearance depending on the plant variety and environmental severity, often leading to a woody texture in the affected tissue layers.

Development and spread of the pathogen are highly favored by neutral to alkaline soil pH levels (above 6.0) and dry, warm soil conditions during the early stages of tuber or root initiation. The pathogen persists in the soil on organic matter and can also be introduced through infested seed stock.

Effective management requires an integrated approach, including the use of crop rotation, planting resistant varieties, and acidifying the soil through specific fertilizer applications. Maintaining adequate soil moisture during the critical period of tuber development is also a vital practice to inhibit infection spread.