2000 Blue Mold Epidemic

in North America

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

The 2000 Blue Mold Epidemic in North America: The North American Plant Disease Forecast Center at North Carolina State University has completed its fifth year of service to tobacco producers, industry, and extension services throughout North America. The forecasts were issued on the Internet three times each week from March through August. Additional forecasts were provided during peak epidemic periods. There is also a toll-free telephone "hot-line" that provides timely forecasts to growers without computers. Timely information of the geographic occurrence of blue mold and on the future movement of inoculum (fungus spores) across the North American continent was important to tobacco producers in managing this destructive and fast moving plant disease epidemic. Users found the maps, 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 on the system!

Blue mold occurred in the majority of the major tobacco production regions of North America during the 2000 growing season. The lack of any official disease reports from South Carolina and Indiana was somewhat surprising. Central and western Tennessee, western Kentucky, and Wisconsin were also notable exceptions. However, blue mold may have occurred in these regions but was simply unreported or undiscovered. Continental forecasting began on March 6 with disease sources in western Cuba and Mexico. A total of 460 forecasts were made on 79 days with the last forecast on August 28, 2000. Disease activity was still present in a few regions at that time. All blue mold samples submitted to the various laboratories for strain testing were insensitive (resistant) to the fungicide metalaxyl. This continued a 3-year period of metalaxyl-insensitive strains of Peronospora tabacina in North America.

The first report of blue mold in the United States was in northern Florida on March 21. Infections were discovered in several plant beds in the northern section of Alachua County. The source of this outbreak was spores released from Cuba on February 26, 2000.

Blue mold was first reported in the flue-cured region of eastern North Carolina on April 14, in Lenoir County. A second outbreak of blue mold in North Carolina's flue-cured region was discovered on April 28, in Moore County in south central NC. Both of these outbreaks occurred in greenhouses, with infected transplants subsequently being taken to the field. Through late April, May, and into early June, blue mold spread to other greenhouse and fields in a broad area of central and eastern North Carolina. In nearly every case, field disease resulted from infected transplants. However, disease activity in the field then increased during periods of favorable weather.

The first report of blue mold in Georgia came from fields in Bacon and Appling Counties in southeast Georgia around April 21. On May 3, and again on May 8, other outbreaks were reported from areas near Tifton, GA and Colquitt, GA, respectively. During May, blue mold became generally distributed across northern Florida. With mostly dry weather prevailing during April and May in the Southeast, disease activity appeared to be driven more by locally favorable conditions (e.g., from irrigation) than from widespread periods of favorable weather.

Blue mold was reported in Tennessee on June 9. The discovery was made in a field in Grainger County in the northeast part of the state. A flurry of initial outbreaks for many states occurred during late June and early July. Blue mold was discovered in southern Ontario, Canada on June 21 on greenhouse seedlings and recent field transplants. The first report from Virginia came the same day, from a field in Washington County in the extreme southwest portion of the state. The first report from the North Carolina burley region came on June 22. This was a field outbreak in Madison County in the central NC mountains. On June 23, the Forecast Center received the first report from Kentucky. Low levels of disease activity were discovered in six counties in east-central and eastern areas of that state. Also on June 23, active lesions were found on tobacco plants in a greenhouse in western Massachusetts, which marked the first outbreak in the southern New England region. The first outbreak in the southeast Pennsylvania growing region was reported on June 28. Blue mold was discovered in several fields in Adams County, Ohio, on July 5. This followed observations indicating that blue mold was present at low levels in much of central and eastern Kentucky.

Initial outbreaks for other tobacco states occurred during the remainder of July. Each new report was near established sources. West Virginia's first report came from Cabell County on July 12. St. Mary's County, in southern Maryland, was the site of Maryland's first report on July 17. Connecticut's first report occurred on July 19. Blue mold was observed on shade tobacco in Tolland County, near the Massachusetts border.

Disease activity increased steadily, sometimes rapidly, in each of the regions that reported their first outbreak in late June or early July. A prime example was the situation in Kentucky and nearby areas of Ohio and West Virginia. In early July, blue mold was active at low levels in central and eastern Kentucky. By August 2, Dr. Nesmith reported a major epidemic of blue mold in eastern Kentucky, southern Ohio, and western West Virginia. This increase in disease activity coincided with a summertime weather pattern that was frequently conducive to afternoon shower and thunderstorm activity. The regions most affected were the Ohio Valley and the mid-Atlantic, northward and eastward to the Great Lakes and the Northeast. There were some short periods of very dry or very rainy weather. Overall, however, many days simply had a decent to good chance of afternoon showers and thunderstorms. Conditions for survivable transport and deposition were mixed to mostly favorable. This proved suitable for local to short-range transport and deposition events, which marked the summer portion of the disease season.

In 2000, blue mold was reported from most of the major tobacco growing areas. Disease activity was low to moderate overall, but locally severe outbreaks could be found in most regions where disease was present. Substantial increases in disease activity occurred in two instances. The first was in late April and May in North Carolina, when blue mold advanced from greenhouse to greenhouse and from greenhouses to the field. The other was over the growing areas from North Carolina and Tennessee northward to southern Canada and the Northeast, lasting from June through August. Once blue mold became established in a new area, persistent weather patterns provided mixed to mostly favorable disease conditions, which gave rise to a steadily advancing epidemic front.

A table of first reports from each state is given below.

First Reports of Blue Mold to the North American Blue Mold Forecast Center in 2000 (a)

County/State	Date Reported	Probable source (b)	Impact (c)
Alachua County, FL	35144	Cuba	?
Lenoir County, NC (flue-cured)	35168	N FL	?
Bacon and Appling Counties, GA	35175	N FL	?
Grainger County, TN	35224	Undetermined	?
Haldimand-Norfolk County, southern Ontario, Canada	35236	Undetermined	?
Washington County, VA	35236	Eastern TN	?
Madison County, NC (burley)	35237	Eastern TN	?
Breathitt, Clark, Fayette, Jessamine, Madison, and Rockcastle Counties, KY	35238	Eastern TN	?
Hampshire County, MA	35238	Undetermined	?
Adams County, OH	35250	Kentucky	?
Cabell County, WV	35257	Kentucky	?
St. Mary's County, MD	35262	Undetermined	?
Tolland County, CT	35268	Massachusetts	?

(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 periodically.

This report represents a short version describing the 2000 North American blue mold epidemic. A more complete report will be available following detailed analysis of all disease reports, meteorological records, and state impact data. The complete set of day-by-day forecasts can be reviewed via the Internet website: 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 2000. If you wish to become part of the Forecast System, or need further information, contact C. E. Main or the Forecast Center directly.

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