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Etiology and Control of Root Diseases of Spinach. Donald R. Sumner, Assistant Professor, Department of Plant Pathology, Coastal Plain Station, Tifton, Georgia 31794; Stanley J. Kays(2), and A. W. Johnson(3). (2)Former Assistant Professor, Department of Horticulture, University of Georgia, Coastal Plain Station, Tifton, Georgia 31794, Current address: Department of Horticultural Food Science, University of Arkansas, Route 6, Fayetteville 72701; (3)Nematologist, Agricultural Research Service, U.S. Department of Agriculture, Coastal Plain Station, Tifton, Georgia 31794. Phytopathology 66:1267-1273. Accepted for publication 27 April 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1267.

Seedling diseases in field tests were more severe in late summer or early fall plantings when soil temperature maxima at 1 cm depths were 25-36 C. Seedling injury also was severe in a winter crop when soil temperature minima were 2.8 C for 2 days in succession 12 days after planting. The fungi most frequently isolated from seedlings were Fusarium oxysporum, F. solani, Pythium spp., Rhizoctonia solani, and F. roseum, in that order. In pathogenicity tests in environmental chambers, R. solani caused the most severe damage, but Pythium irregulare, F. oxysporum, and F. roseum also caused significant root injury. Populations of F. oxysporum and Pythium spp. were reduced and seedling diseases and injury by root-knot, stubby-root, and ring nematodes decreased by soil fumigation with DD-MENCS and methyl bromide-chloropicrin (2:1, v/v). Soil fumigation sometimes decreased the incidence and severity of yellows and decline and increased yields, but results were variable. Symptoms of decline were associated with nutritional imbalance, wet soil, prolonged cloudiness, abrupt temperature changes, nematodes, and soil-borne fungi, but were not typical of Fusarium wilt.

Additional keywords: Spinacia oleracea, Meloidogyne incognita, Trichodorus christiei, Criconemoides ornatus, ethoprop, benomyl, chloroneb.