Epidemiology of blue mould (Peronospora tabacina Adam)

Abstract

The occurrence of blue mould disease of tobacco in the Ovens Valley district of Victoria was recorded at intervals of 2 weeks in observation rows during six successive seasons. First appearance of the disease was not associated with any particular plant growth stage or time of the year. There was an association with infected transplants and with wet days in the two preceding weeks. Subsequent increase in the number of diseased plants was related to rain on two of three consecutive days. The highest percentages of plants with disease occurred in plots where symptoms appeared before December 24. The percentage of plants with blue mould increased up to the commencement of flowering, usually late in January. There was a time interval of 2–5 weeks from first appearance to maximum percentage of plants diseased, the shorter period occurring when more than 25% of plants were diseased at the first record. The rate of spread of disease between fields was proportional to the number of fields already infected. The disease spread more slowly when the plants were sprayed with fungicides.