1999 Blue Mold Epidemic in North America
North American Blue Mold Forecast Center
Department of Plant Pathology
North Carolina State University
Raleigh, NC
The North American Blue Mold 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 three times each week from March through September. Additional forecasts were provided during peak epidemic periods. Timely information on the geographic occurrence of blue mold and 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 almost all of the major production regions of North America during the 1999 growing season. The lone exception was southern Ontario, Canada. Continental forecasting began on March 5 with disease sources in western Cuba and Mexico. A total of 527 forecasts were made on 87 days with the last forecast on September 23, 1999. Some disease activity remained in eastern Kentucky, the southern Appalachian Mountains, and southern New England at that time. As in recent years, nearly all blue mold samples submitted to the various laboratories for strain testing were insensitive (resistant) to the fungicide metalaxyl.
Pervasive and continuing drought in the Southeast, Mid-Atlantic, and Ohio Valley regions of the United States was the prime governing factor in moderating this year's epidemic. Extended periods of favorable weather in any one region were very unusual. Disease activity tended to be highly variable and was often hindered or arrested by lack of moisture and/or hot summertime temperatures. Blue mold infections were reported from most growing regions and became scattered across several of them. However, some areas that normally report the disease experienced no blue mold this year. In addition, light to moderate activity levels were typical; severe cases were few in number. Most outbreaks generally tended to be dependent on local favorable conditions, such as shade from trees or irrigation, rather than broadscale, consistently favorable weather.
The first reports of blue mold in the United States came from southern Georgia on March 12 and northern Florida on March 19. All reports were from plant beds or greenhouses. The source of these outbreaks was spores from western Cuba on or about February 16-17.
Disease activity increased in greenhouses and plant beds across southern Georgia, becoming common by early April, and then declined during the remainder of the month. Field activity was low during most of March and April due to dry conditions coupled with cool overnight temperatures. No other report of new outbreaks of blue mold were received during March or April.
Blue mold became established in irrigated fields of southern Georgia in mid-to-late April. Two short periods of favorable weather in late April and early May were followed by unfavorable weather for several weeks. Blue mold was slowly increasing in northern Florida. Georgia field activity increased as well, becoming moderately active and scattered over the entire Georgia growing belt by May 21.
Late May through mid-June was dry with occasional one-day or two-day periods of favorable weather for some areas. First reports of blue mold for areas north of Georgia/Florida came during this period. The initial report from flue-cured areas of North Carolina occurred on May 26. First report from South Carolina was on May 28. Blue mold was reported in southeast Kentucky on May 31. Additional reports from south-central North Carolina and Shelbyville, KY were received on June 2.
The closest resemblance to a period of widespread favorable weather occurred from mid-June to July 2nd, interspersed with an unfavorable period from June 18 through June 23. Due to slow-moving cold fronts, conditions remained favorable for several days at a time over much of the eastern United States. Disease activity increased in Kentucky and eastern North Carolina. Blue mold was reported from the central North Carolina mountains (burley) on June 16. Blue mold was reported in central Tennessee on June 23.
All of the other U.S. areas affected in 1999 reported outbreaks in July, following this two-week period of favorable weather: Connecticut on July 2, Pennsylavania on July 9, Maryland on July 16, southwest Virginia on July 19,Massachusetts and Indiana on July 23, and Ohio on July 30. After July 2 and through the month, typical summertime weather patterns became firmly established. Hot, dry conditions were dominant with sporadic short periods of disease-favorable weather in some locations. Conditions were favorable more frequently in the southern Appalachian Mountains than other areas resulting in significant increases in disease activity. Blue mold was present at low levels throughout much of Kentucky with more intense disease activity in some spots. Disease activity diminished in many regions as unfavorable weather continued.
Conditions in August and September were largely a continuation of those established during July. Blue mold remained active in southern New England, the southern Appalachian Mountains, and parts of the Ohio Valley. These areas received occasional showers. The disease slowed or stopped in the Mid-Atlantic states. Forecasting was discontinued on September 23.
There were several significant transport episodes in 1999. The first occurred sometime during mid to late February, when viable spores from western Cuba were deposited in the southern Georgia / northern Florida region. The second significant transport event occurred on May 5 and May 6 during a short period of favorable weather. Spores from the southern Georgia and northern Florida region were likely responsible for first outbreaks in eastern NC, eastern SC, western NC, and eastern KY. The Pennsylvania outbreak probably arose from the episode of June 2, from Kentucky. Blue mold cases in Connecticut and Maryland were likely due to a transport episode (or episodes?) from eastern North Carolina the weekend of June 25-27. Other outbreaks in Tennessee, Virginia, Massachusetts, Indiana, and Ohio were the result of local and/or short-range transport events.
The last significant transport event is one that did NOT occur. It's one that would have brought blue mold to southern Ontario, Canada. No blue mold was reported from this region in 1999 despite frequent observers scouting in the fields. This was most likely a case of good fortune. Only two forecasts showed trajectories threatening to this region, one on May 31, the other on August 12. Southern Ontario was at Moderate Risk both times. In each case, conditions at the threatening source region had been unfavorable days beforehand. Thus, its likely fewer airborne spores were present in those instances than at other times.
Disease activity in 1999 was limited in scope and intensity. This was both directly and indirectly related to the extensive drought in the eastern United States. The predominantly sunny weather made spore survival unlikely during transport in many cases, thereby limiting the potential for long-range transport. Dry, hot conditions stressed the tobacco plants and reduced sporulation. The lack of extended periods of favorable weather within any one region prevented the buildup of huge spore loads and decreased the occurrence of explosive, damaging disease development. The result was a fairly widespread but mostly less intense blue mold season in 1999.
This report represents a brief description of the 1999 North American epidemic. A more complete report will be available following 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 1999. If you wish to become part of the Forecast System, or need further information, contact C. E. Main or the Forecast Center directly.
First Reports of Blue Mold to the North American Blue Mold Forecast Center in 1999 (a)
| County/State | Date Reported | Probable source (b) | Impact (c) |
| Grady, Echols, and Colquitt Counties, GA | 12 March | Cuba | ? |
| Columbia County, FL | 19 March | Cuba | ? |
| Jones County, NC (flue-cured | 25 May | S Georgia / N Florida | ? |
| Williamsburg County, SC | 26 May | S Georgia / N Florida | ? |
| Clay County, KY | 31 May | S Georgia / N Florida | ? |
| Madison County, NC (burley) | 16 June | S Georgia / N Florida | ? |
| Montgomery County, TN | 22 June | Kentucky | ? |
| Hartford County, CT | 2 July | Eastern North Carolina | ? |
| Lancaster County, PA | 9 July | Kentucky | ? |
| St. Mary's County, MD | 16 July | Eastern North Carolina | ? |
| Lee and Washington Counties, VA | 16 July | Western North Carolina | ? |
| Hampden County, MA | 23 July | Connecticut | ? |
| Jefferson County, IN | 23 July | Kentucky | ? |
| Brown County, OH | 29 July | Kentucky | ? |
(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.
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This page was constructed by Gail Kampmeier at gkamp[at]uiuc.edu
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