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A minor blue mold outbreak in Shelby, Henry and Oldham counties is a late-season reminder to tobacco farmers not to let their guards down just yet.
Kenny Seebold, plant pathologist in the University of Kentucky College of Agriculture, said it is unclear how much of the disease is out there. The confirmed sightings have occurred in a fairly tight-knit area around the adjoining borders of the three counties. Sporulating lesions were present in the Oldham County sample, as well as in an earlier sample taken near Chestnut Grove in Shelby County. The Shelby County plants showed lesions that appeared to be seven to 10 days old.
He thinks that last week’s cooler temperatures along with a few showers were prime conditions for blue mold development and spread.
Such weather will significantly slow down not only the speed at which the disease develops but how far it spreads. Blue mold is caused by Peronospora tabacina, an airborne fungus that prefers cool, humid conditions.
Seebold assesses the risk level as low to moderate.
Also working in farmers’ favor is the timing of the outbreak. The latest figures from the U.S. Department of Agriculture indicate that 11 percent of Kentucky’s tobacco has been harvested and 64 percent topped. Topped tobacco and plants treated for suckers are less susceptible to the fungus, which leaves a grayish-blue mildew on the undersides of leaves.
Due to weather patterns, untopped tobacco southeast of the infected counties could be most affected by the outbreak. Seebold said farmers should base their decisions to apply fungicides on the age of the crop and whether a particular field lies in the path of spores.
The appearance of a lot of target spot, another fungal disease, is also a reason for applying a fungicide application.
He said observers have seen a big jump in target spot activity over the past two weeks, particularly in low-lying. He recommends Quadris at a rate of eight or more ounces per acre. With good coverage, this application should give a couple of weeks’ protection against blue mold and target spot.
For more information on controlling fungal diseases in tobacco, contact your local Cooperative Extension office or consult the Kentucky Tobacco Disease Information Web site, http://www.uky.edu/Ag/kpn/kyblue/kyblue.htm.