Common Scab (Streptomyces spp.):

The disease does not cause yield losses but disfigures the tubers, thereby reducing the market value and increasing peeling losses. The disease mainly affects potato tubers causing any of the following symptoms viz., mere abrasion of skin (russetting); corky lesions around lenticels which may be star shaped or irregularly circular; irregular concentric corky rings around lenticels; raised rough corky pustules and 3-4 mm deep pits surrounded by hard corky tissues. In case of severe attack, dark brown lesions may develop on roots and stolons.

Control:

The pathogen is difficult to control because of long survival both on seed tubers and in soils. However using disease free seed tubers could minimize the disease incidence. Before planting the seed tubers are treated with organomercurial compounds (0.015%for 20 minutes) or Boric Acid (3% for 30 minutes) and dries in shade. The same treatment is repeated before the storage of the tubers. Maintaining high moisture in ridge atleast for a few weeks during the initial tuber formation phase crates adverse conditions for the development of the disease. Following crop rotations with wheat, pea, oats, barley, lupin, soybean, sorghum and bajra checks the disease development.