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Influence of Soil Moisture and Fungicide Treatments on Common Scab and Mineral Content of Potatoes. J. R. Davis, Associate Professor of Plant Pathology, University of Idaho, Idaho 83210; G. M. McMaster(2), R. H. Callihan(3), F. H. Nissley(4), and J. J. Pavek(5). (2)(3)(4)Professor of Agricultural Engineering, Assistant Professor of Agronomy, and Scientific Aide, University of Idaho, Idaho 83210; (5)Research Geneticist, Agricultural Research Service, U.S. Dept. of Agriculture, Research and Extension Center, Aberdeen, Idaho 83210. Phytopathology 66:228-233. Accepted for publication 16 August 1975. DOI: 10.1094/Phyto-66-228.

Irrigation and fungicide treatments were tested for their effect on common scab (caused by Streptomyces scabies) on two potato clones (Russet Burbank and A6371-2). Significantly less scab resulted with irrigation throughout the growing season at either 0.45 or 0.65 bars of soil moisture tension than with irrigation at 0.96 or 1.60 bars. Irrigation at 0.65 bars appeared suitable for maximum potato production. Lesions on tubers irrigated at 1.60 bars were significantly deeper than lesions on tubers irrigated at either 0.96 or 0.65 bars. Treatments with pentachloronitrobenzene (PCNB) at 17, 22, or 28 kg/hectare (ha) and treatments with sulfur at 450, 670, or 900 kg/ha reduced scab. However, when soil moisture was allowed to drop to 1.60 bars, the percentage of scab-free potatoes in fungicide-treated plots was not significantly different from untreated plots. Nutrient analyses of petioles collected in July showed that scab severity was positively correlated with calcium and negatively correlated with potassium, phosphate, and manganese. Tubers grown with moisture depletion to 1.60 bars showed more calcium in the peel than tubers grown with lower moisture tensions, but no significant effect was observed on potassium, phosphate, or manganese.

Additional keywords: nutrition.