VIEW ARTICLE

Disease Control and Pest Management

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.