Scab (fungus - Streptomyces scabies): Rough, corky areas that may be round or irregular occur on tubers. Injury does not extend far into the potato but the appearance is objectional. Scab is less prevalent in acid soils than in alkaline. Avoid alkaline soil amendments such as manure, lime, or ashes. Avoid severely infested fields. Apply heavy irrigation at the time of tuber or early root formation. Use a 4 to 6 year rotation under irrigation. A 3- to 4-year rotation is satisfactory under dry land conditions. Use certified seed of scab resistant varieties. Treat seedpieces (See in the chapter on "Seed Treatment"). Wire worm damage, commonly called "deep scab", is not a disease. It differs in that the pits are deep and tissue has been removed by insect feeding. Sulfur may be used in home gardens to make the soil more acid.
