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Forecasting Onion White Rot Disease. P. B. Adams, Research plant pathologist, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705; Phytopathology 71:1178-1181. Accepted for publication 27 February 1981. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1981. DOI: 10.1094/Phyto-71-1178.

Sclerotia of Sclerotium cepivorum were uniformly distributed in the top 2025 cm of soil in fields in southern New Jersey, which corresponds to the depths to which farmers plow. Fields were not uniformly infested with S. cepivorum; inoculum densities differed by as much as 34 sclerotia per 100 g of soil in adjacent 0.2-ha field plots. A highly significant (P = 0.01) correlation (R = 0.71) was found between the inoculum density of S. cepivorum at the time of planting and white rot incidence at harvest. This relationship could be expressed as Y = 6.41 + 12.38X 0.65X2, where Y = percentage white rot of bunching onions and X = number of sclerotia per 100 g of soil. Leeks were more resistant than bunching onions to white rot; Walla Walla Sweet Spanish bulb onion was intermediate in resistance.

Additional keywords: Allium spp.