2002 Blue Mold Epidemic in North America

The North American Plant Disease Forecast Center at North Carolina State University completes its seventh 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 2002 growing season. We also received a report this year from the Dominican Republic. No official reports were received from South Carolina, Indiana, or Wisconsin. Continental forecasting began on March 4 with disease sources in western Cuba and Mexico. 474 forecasts were made on 76 days. The last forecast was made on August 30, 2002. Disease activity was still present in a few regions 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.

Dry and hot was the meteorological theme for most growing regions in 2002. Long-term drought continued (and in many areas worsened) over the Southeast and mid-Atlantic regions. Extended periods of favorable weather did not occur in most areas. Where they did occur they were very few in number. Unfavorable weather dominated in the Southeast and mid-Atlantic regions from March through May. Dry periods were interspersed with episodes of mixed to favorable conditions as weather fronts passed through the eastern United States. Most of the mid-Atlantic region continued to experience dry weather throughout the summer. Locations in the Northeast, southern Canada, the southern Appalachian Mountains, and the Ohio Valley were mostly dry through May. These regions experienced more shower activity during the summer, associated with passing cold fronts that later dissipated after moving east of the Appalachian Mountains. Growing areas in the Southeast also had frequent shower activity in the summer after a relatively dry spring.

The 2002 blue mold epidemic spread steadily from the Southeast into the mid-Atlantic during the March to May period. The first report of blue mold from the United States was from Tift County in southern Georgia on March 22. Disease occurred in plant beds. There was evidence of systemic infection, indicating blue mold had been present for several weeks. Observations on March 31 revealed Florida's first outbreak on plant beds in Hamilton County. North Carolina's first report from the flue-cured region occurred early compared to most years. This was in Franklin County on April 12. The initial report from Virginia was on the sixth of May, from greenhouses in Brunswick and Dinwiddie Counties. By May 30, the epidemic had reached Lancaster County, Pennsylvania plant beds. All of these outbreaks occurred in greenhouses or plant beds. As was the case in the 2000 and 2001 seasons, this illustrated the ability of blue mold epidemics to spread despite pervasive dry conditions. Field infections from March through May developed slowly at most locations due to the dry weather.

Blue mold outbreaks occurred west and north of these early-season areas during the summer. Soon after the Pennsylvania report, blue mold was discovered near Jonesborough, TN on June 7. This was the first report from Tennessee (and the southern Appalachian Mountain region). Fresh and heavy sporulation was occurring in float beds. The first report from the southern New England region was received on June 26. Two generations of lesions were present on shade tobacco in Hartford County, CT. Casey and Taylor Counties were the site of Kentucky's first outbreak, reported on June 28. The plants had been set in the field in late May. Available evidence indicated that systemic infection occurred within a few days of setting following a period of favorable weather.

Short-range transport and deposition were likely responsible for outbreaks that occurred in late June or early July. First reports were received from Massachusetts (Hampden and Hampshire counties) and the burley areas of western NC (Avery and Watauga Counties) and extreme southwest Virginia (Washington County). The weather had turned mostly favorable for disease development in these two regions during the latter part of June.

The first report from Canada arrived at the Forecast Center on July 30. One generation of lesions was found on tobacco in Brant County, in southern Ontario. A transport event from southeast Pennsylvania on July 25 was noted regarding potential transport and deposition in southern Ontario. If this event were to be held responsible for the southern Canada outbreak, it would imply a five-day latent period before the appearance of the first lesions. Normal latent periods are 7-10 days. Perhaps another (as yet unexplained) transport event was responsible for Canada's first outbreak.

Low levels of disease activity were the norm in 2002 due to the widespread drought that occurred in most locations. Field infections developed slowly. As in other mostly dry years (2000, 2001), increased disease severity appeared to be more dependent on local situations than on prevailing weather patterns. Higher levels of disease activity were largely isolated. These were found in shady sections of some fields or in irrigated areas, while adjacent plants might have shown few or no symptoms.

The nature of this year's rainfall events also played a part in disease distribution. The majority of these events consisted of shower activity associated with passing cold fronts. Periods of steady rain were a rare occurrence. Mixed conditions for survivable transport and deposition were typical of most disease-development scenarios. In addition, once blue mold became established in a new location, localized and short-range disease development was highly dependent on succeeding shower events. Resulting infections tended to be scattered and highly variable in nature. For example, blue mold spread across the southern Appalachian Mountain region during late June and July, when scattered afternoon showers and thunderstorms occurred on a fairly frequent basis. Yet, areas of light activity were situated next to neighboring fields where blue mold was raging. Similar situations were observed in the Ohio Valley.

In 2002, blue mold was reported from most of the tobacco growing regions. Disease activity was light overall. Isolated areas experienced more intense damage. Activity was quite variable in some areas, with local conditions playing a significant role. Hot and mostly dry weather was the norm for much of the season in many locations. Compared to years with more normal rainfall, the largely unfavorable weather conditions had greater impact on the epidemic's intensity and lesser impact on its spread, though both were hindered. Epidemics in 2000 and 2001 also showed these traits. A table of first reports from each state is given below.

This represents a short report describing the 2002 North American blue mold epidemic. A more complete report will be available 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 2002. 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 2002 (a)

County/State	Date Reported	Probable source (b)	Impact (c)
Tift County, GA	March 22	Cuba	?
Hamilton County, FL	April 2	Cuba / (southern GA?)	?
Franklin County, NC (flue-cured)	April 12	Southern GA / northern FL	?
Brunswick / Dinwiddie Counties, VA	May 6	Eastern NC? / southern GA - northern FL?	?
Lancaster / Chester Counties, PA	May 30	Eastern NC / south-central VA	?
Washington County, TN	June 7	Undetermined, possibly multiple	?
Hartford County, CT	June 26	Southeast PA and/or southern mid-Atlantic area	?
Casey / Taylor Counties, KY	June 28	undetermined	?
Hampden / Hampshire Counties, MA	July 5	Connecticut	?
Watauga / Avery Counties, NC (burley)	July 10	Neighboring areas of Southern Appalachian Mountains	?
Brant County, southern Ontario, Canada	July 30	Pennsylvania / other?	?
Brown County, OH	August 1	Kentucky	?

• (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.