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Rainfall, Irrigation Water, and Temperatures Associated with First Occurrences of Tobacco Blue Mold in Leaf Production Area of North Florida from 1979 to 1984. T. A. Kucharek, Professor, Plant Pathology Department, University of Florida, Gainesville 32611. Plant Dis. 71:336-339. Accepted for publication 27 August 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0336.

Blue mold of tobacco occurred in north Florida in transplant beds or fields each year from 1979 to 1984. Average daily minimum temperatures for 10, 20, and 30 days prior to first disease occurrences at different sites varied considerably. Days achieving 30 C or greater or 7.8 C or less, both temperatures reported to have deleterious effects on the pathogen, were as high as 23 and 21, respectively, for 30 days prior to the appearance of the disease. For 10 days prior to occurrence of disease, days achieving these same temperatures were as high as 8 and 9, respectively. Of 18 sites studied, 14 sites had rainfall amounts in excess, some by a factor of two or three, of the normal for the 30 days prior to disease occurrence. Three of the remaining four sites also had excessive moisture when overhead irrigation was considered. One of these three sites had three adjacent tobacco fields with different blue mold severities that corresponded to the irrigation amounts and numbers. One of these fields, which was between the other two, had no blue mold and it received the least amount of irrigation. Because of the apparent wide temperature regimes and high rainfall or irrigation amounts associated with first blue mold appearances, moisture appears to be the stronger of the two variables in relation to blue mold occurrence in north Florida.

Keyword(s): Nicotiana tabacum, Peronospora tabacina.