Origin
Transport events from the source in PA were examined to determine if this source region was the origination of the infection in NC, where first symptoms are estimated to have appeared around June 12. Events both before and after the source in PA became known were considered.
A highly plausible candidate for the outbreak has not emerged; more analysis is being performed. Only 2 events from the PA source region move anywhere close to Forsyth County. These are the events of June 4 and June 5, before the source in southeast PA was discovered. Neither event inspires confidence. Each event would have taken 2 days to reach west-central NC. The source was weak. Precipitation data reveals a significant amount of rainfall between the source and Forsyth County, and thus washout of many airborne spores prior to potential arrival in NC was highly likely. This last point is supported by air concentration and deposition analysis from two separate meteorological data sets.
No other outbreaks between southern PA and west-central NC have been reported. All other transport events from southeast PA moved well away from Forsyth County. Other than the timing of the June 4 / June 5 events from southeast PA, other evidence indicates that these, also, are unlikely. Failing an adequate explanation that may yet be revealed via airborne transport, the other alternatives involve transport from an undiscovered or unreported source, or introduction of disease by another mechanism.
Potential impact
Trajectories from the new NC source location were examined for the time period of June 8 through June 27, to determine whether any of these transport events may have impacted other areas. Of these 20 events, 13 moved between northeast and southeast. Weather conditions likely showed substantial variation. Live spores may have been deposited in portions of southside VA, central and eastern NC, or northeast SC during these events. Four events moved to the south, probably with little impact. One event remained close to the source.
The two remaining events are the most noteworthy. One, on June 15, move NNW toward western VA and west Virginia. The other, on June 16, move west and then north through western NC, northeast TN, and extreme western VA. Rainfall data shows plentiful amounts during these events. Some spores were likely washed out near the source. Others, however, may have been deposited in the burley-growing region of the southern Appalachian Mountains. Growers here should be especially watchful of their plants.
TK