exec2004 blue mold report

2004 Blue Mold Epidemic in North America

Annual Report from the North American Plant Disease Forecast Center

October 8, 2004

Dr. C. E. Main and T. Keever
North American Plant Disease Forecast Center
Department of Plant Pathology
North Carolina State University
Raleigh, NC

The North American Plant Disease Forecast Center at North Carolina State University completes its ninth year of service to tobacco producers, industry, and extension services throughout North America. The forecasts are issued on the Internet three times each week from March through August. Additional forecasts are provided during peak epidemic periods. There is also a toll-free telephone "hot-line" that provides timely forecasts to growers who don't own computers. Timely information on the geographic occurrence of blue mold and on the impending movement of inoculum (fungus spores) across the North American continent is important to tobacco producers in managing this destructive and fast moving plant disease epidemic. Users find the maps, disease outlooks, and other information helpful in determining the time of arrival of spores and assessing the risk for their production areas. As always, we are interested in your comments or suggestions on the forecast system!

Blue mold occurred in most of the tobacco production regions of North America during the 2004 growing season. The Forecast Center received no official reports from Florida, Georgia, South Carolina, the flue-cured areas of North Carolina, Maryland, or Pennsylvania. 2004 was the first year out of 9 in which no reports were received from Florida or Georgia. Continental forecasting began on March 8 with confirmed disease sources in western Cuba and Mexico, plus southern Texas (confirmed in late April). 292 forecasts were made on 63 days. The last forecast was made on August 16, 2004. Disease activity was still present in many areas at that time. Nearly all disease samples submitted to the various laboratories for pathogenic strain testing were insensitive (resistant) to the fungicide metalaxyl. This is consistent with our experience since 1991, when metalaxyl-insensitive strains of Peronospora tabacina became dominant during the yearly epidemics in North America.

The 2004 disease season was historically unusual in several ways. The first report of blue mold from the major production areas arrived in late Spring on May 25. The report came from central Kentucky. This contrasted sharply with the epidemic spread of the previous 8 years in which the first report in U.S. production came from northern Florida or southern GA during March or April. There was also virtually no disease reported east of the Appalachian Mountains, from southern Pennsylvania through the southeastern states. The lone exceptions were weak, isolated outbreaks in Rockingham County in northern North Carolina and nearby Pittsylvania County along southside Virginia.

The first report of blue mold came in late May from Taylor, Green, and Jessamine counties in central Kentucky. There were a number of other reports over the next 3 weeks that lay in a swath of counties from north-central Tennessee northeastward through northern Kentucky. Observations at the various outbreak sites indicated that most initial infections occurred during the same time period, from late May through early June. Blue mold spread to the southern Appalachian Mountains (scattered counties in Tennessee, North Carolina, and extreme southwestern Virginia) during mid to late June. Disease developed in southern Ohio in late June and was reported in western West Virginia by July 12. The first reports of blue mold outside of the Ohio Valley and southern mountain regions occurred in early August: Massachusetts on August 3, southern Wisconsin on August 4, and southern Ontario, Canada on August 5. Connecticut’s first report arrived on August 24.

The Ohio Valley was hit hard by the 2004 epidemic. An extended period of wet weather occurred in this region from late May through early July. In mid-June there were 11 counties in Kentucky reporting blue mold. By July 19 there were 70 counties reporting blue mold in Kentucky, plus 9 in north-central Tennessee, 5 in southern Ohio, 3 in western WV, and several in southeast Indiana. Although there was the typical variation in disease activity from field to field and county to county, historically high levels of disease were observed in many areas. By season’s end over 90 counties in Kentucky had confirmed blue mold. Epidemic spread in the Ohio Valley was worsened considerably by the movement of infected transplants. The weather in the Ohio Valley and southern Appalachian Mountains was more variable from mid-July through August. Disease activity remained strong in most areas, especially in the Ohio Valley. Outbreaks in Wisconsin, southern Ontario, and southern New England likely resulted from airborne transport events from one or both of these areas during mid to late July.

The weather patterns in 2004 had a direct bearing on the course of this year’s epidemic. For much of the spring and summer, high pressure was situated over the western Atlantic and southeast United States. Easterly winds constantly pushed airborne spores from Cuba westward or northwestward into the Gulf of Mexico. There were only 2 occasions in which trajectories from western Cuba moved near the northern FL / southern GA growing regions (one in mid-February, another on April 10 and 11). Both events were Low Threat / Low Risk and neither brought blue mold to its usual foothold in the Southeast. The dominant high pressure areas also served to slow or stall frontal boundaries in many instances. This resulted in prolonged wet weather from late May through early July for the Ohio Valley and southern Appalachian Mountains. The highly conducive conditions for disease development led to the explosion of the blue mold epidemic during this period. Finally, the prevailing atmospheric patterns were such that there were no extended periods of hot or dry weather which might have served to slow or stop the epidemic’s progress.

The 2004 blue mold epidemic was quite different as compared to the previous 8 years. Disease arrived in the United States very late, in late May versus March or April. The first report came out of central Kentucky instead of northern Florida or southern Georgia. The mid-Atlantic and Southeast regions were virtually absent of disease east of the mountains. A prolonged period of wet weather during the late spring and early summer gave rise to an intense epidemic in the Ohio Valley growing region.

This represents a short report describing the 2004 North American blue mold epidemic. This report may be updated at a later date following detailed analysis of all disease reports, meteorological records, and state impact data. The complete set of day-by-day forecasts can be reviewed on this Internet site: http://www.ces.ncsu.edu/depts/pp/bluemold/.

The North American Blue Mold Forecast Center thanks all the reporting Coordinators for each US state and adjoining countries for their participation during 2004. If you wish to become part of the Forecast System, or need further information, contact C. E. Main or the Forecast Center directly. For a complete description of the Plant Disease Forecast Center, refer to the APSNet feature article "Forecasting Long-range Transport of Downy Mildew Spores and Plant Disease Epidemics" at http://www.apsnet.org/online/feature/forecast/top.htm.

First Reports of Blue Mold to the North American Blue Mold Forecast Center in 2004 (a)

County/State	Date Reported	Probable source (b)	Impact (c)
Taylor County, KY	May 25	Texas?	?
Macon County, TN	June 4	Texas?	?
Union / Claiborne County, TN (Appalachian Mountains)	June 8	Ohio Valley	?
Rockingham County, NC	June 14	Ohio Valley	?
Madison County, NC (mountains)	June 21	Northeast TN or Ohio Valley. (Infected transplants?)	?
Adams County, Ohio	June 21	Ohio Valley (KY)	?
Pittsylvania County, VA	June 23	Ohio Valley or northeast TN. (North-central NC?)	?
Lee County, VA	June 24	Nearby Southern Appalachian Mountains	?
Cabell, Wayne, Putnam counties, WV	July 12	One or more sources in KY	?
Franklin County, MA	August 3	Ohio Valley	?
Dane County, WI	August 4	Ohio Valley	?
Norfolk County, southern Ontario, Canada	August 5	Ohio Valley	?
Hartford County, CT	August 24	Massachusetts. (Ohio Valley?)	?

(a) Occurrence confirmed by a state coordinator or other expert.
(b) Some first occurrences could be the result of multiple sources.
(c) We will continue to update this table as additional reports and impact information come in to the Forecast Center. Please check here periodically.