A REGIONAL-ANALYSIS OF THE METEOROLOGICAL ASPECTS OF THE SPREAD AND DEVELOPMENT OF BLUE MOLD ON TOBACCO

Tobacco mold caused by Peronospora tabacina is a highly weather sensitive disease which occurred in the major tobacco production areas of North Carolina [USA] in 1980. Dates of first reported occurrence of blue mold by county units in eastern North Carolina progressed in a northeastward direction from the South Carolina border to the Virginia border between 1 May and 6 June. In the central piedmont region of the state, blue mold was first reported in mid-May while in the western mountains blue mold was recorded in early June. Temperatures and total weekly rainfall data were analyzed for 18 wk from late March to early Aug. from 102 weather stations across North Carolina and from the bordering regions of surrounding states. An analysis of first occurrence dates and the temporal and spatial properties of temperature and precipitation indicated that the epidemic continued to spread despite temperatures outside the range previously considered favorable for the disease. Availability of moisture on the tobacco leaves for spore germination appeared to be the predominant factor in all parts of the state. Trajectory analysis was used to identify possible source regions for the spores which arrived over North Carolina tobacco fields. There were many days in April, May and June 1980 when conditions were considered favorable for spore transport to North Carolina from the infected fields located to the south. Taking into account epidemiological latent periods, certain of these trajectory dates were selected as representing the most probable periods of spore transport.