Blue mold outbreak found in tobacco fields east of LaRue

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Stay alert to state blue mold warning system

By David Harrison

A fairly significant outbreak of blue mold has been found in several fields east of LaRue County in Clark, Montgomery and Fleming counties. The disease appeared to have started in early July. The incidence and severity of blue mold was quite high. Actively sporulating lesions were abundant, making this a strong source for blue mold to spread.

The areas facing the strongest threat of blue mold are in the immediate area of Clark and Montgomery counties and eastward, but everyone should be aware that an outbreak is possible. Where the threat is most imminent, growers have been advised to begin application of fungicides as quickly as possible to help protect tobacco and to contain the outbreak. Such is not the current situation here.

If blue mold is active on tobacco at the time of fungicide application, treat with Quadris at 12 fluid ounces per acre. For protective sprays use 8-10 fluid ounces per acre. Growers may also use the combination of mancozeb (Dithane, Penncozeb, or Manzate) plus dimethomorph (Acrobat or Forum). In this case, apply two pounds per acre of mancozeb and 3-7 ounces per acre of dimethomorph (user higher rates on bigger tobacco or if active disease is found). Actigard will probably not be a good choice in the areas affected by the blue mold warning, as they may have been exposed to the pathogen, and Actigard needs to be in place four or five days before exposure to the blue mold pathogen in order to activate plant defenses.

When applying fungicides for control of blue mold, good coverage is critical for getting adequate control of disease – this means using an appropriate application volume and drop nozzles to get fungicide materials down into the lower plant canopy. The need to get after blue mold is really strong in the threatened area, because there have been very favorable conditions for blue mold with the cooler-than-normal day and night temperatures, and mostly clear days. Long-distance transport will not be favorable, particularly in areas west of the outbreak such as LaRue County. But an outbreak locally could result in an explosion of blue mold within a field that has the disease and also short distances from these fields, mainly due to very favorable night-time temperatures.

Another point to consider is that tobacco that has been topped, or will be topped in a few days, will be less susceptible to blue mold, and may not need an application of fungicide. However, blue mold loves suckers, so good sucker control will be important.

Finally, as mentioned previously, in areas west of the current outbreak such as LaRue County, the need to protect against blue mold is not as critical. Those wishing to “play it safe” can follow the protectant guidelines listed above. If Quadris is used, they also can count on protection against target spot and frogeye if these diseases are present, which there are reports of.  The other approach is to monitor the blue mold situation and be prepared to spray immediately if movement is predicted from known sources of blue mold, or when blue mold is first found.

If the blue mold situation changes, it will be posted as an alert through the Kentucky Blue Mold Warning System and on the Kentucky Tobacco Disease Information Page (www.uky.edu/Ag/KPN/kyblue/kyblue.htm).