Etiology and Control of Root Diseases of Spinach

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Abstract
Seedling [spinach, Spinacia oleracea] 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.degree. C. Seedling injury also was severe in a winter crop when soil temperature minima were -2.8.degree. 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 funigation with DD[dichloropropene-dichlorpropane]-MENCS and methyl bromide-chloropicrin (2:1 vol/vol). 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.

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