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Fertilizer Effects on Common Scab of Potato and the Relation of Calcium and Phosphate-Phosphorus. J. R. Davis, Associate Professor of Plant Pathology, University of Idaho College of Agriculture Research and Extension Center, Aberdeen 83210; R. E. McDole(2), and R. H. Callihan(3). (2)(3)Associate Professor of Soils, and Assistant Professor of Agronomy, University of Idaho College of Agriculture Research and Extension Center, Aberdeen 83210. Phytopathology 66:1236-1241. Accepted for publication 12 March 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1236.

Results showed significant linear correlations between common scab (caused by Streptomyces scabies) of potato and the Ca, PO4, Mn, and Fe content of tuber peelings. Treatments with nitrate and ammonium fertilizers and the nitrogen stabilizer, N-Serve [2-chloro-6-(trichloromethyl)-pyridine] at 0.6, 1.1, and 1.7 kg/ha with ammonium sulfate (200 kg N/ha) did not significantly affect scab severity. Treatment with N-Serve, however, reduced Mn, Mg, Cu, Zn, and K in potato tissue; and B was increased. Treatments with triple-superphosphate (84 to 336 kg P2O5/ha) significantly reduced the extent of scab and significantly changed scab lesion morphology by reducing lesion height and depth. The effect of triple-superphosphate on potato scab appeared to be indirect, since the pathogen (S. scabies) was not inhibited by triple-superphosphate. Levels of P in potato petioles and peelings were linearly correlated with common scab. The effect of phosphate-P was related to calcium levels and results with phosphate-P suggest a phosphate-calcium interaction. Foliar sprays with manganese (0.2 kg/ha) also were shown to produce a slight, but significant scab reduction.

Additional keywords: Russet Burbank, calcium, phosphate, manganese, N-Serve, N-form.