Blue mold was confirmed on burley tobacco samples from Lewis and Mason counties on August 18, 2014. Samples included multiple leaves with both older (at least 10-day-old) lesions and new lesions with active sporulation (Figures 1 and 2). Samples just received in the Plant Disease Diagnostic Laboratory from Clay County have also been confirmed with active blue mold sporulation.
Recent weather conditions have been favorable for disease development and suggest that un-topped or recently topped tobacco crops in the area east of I-75 are at significant risk for development of the disease. Un-topped or recently topped crops outside this area are also at some risk for disease development. Crops that have been topped at least 7 to 10 days are at reduced risk for disease development. However, given the suspected age of the lesions, the disease has been active for a while, thus, lesion development on recently topped tobacco that was infected prior to topping is possible. Higher temperatures are forecast for later this week, thus, weather conditions may become less favorable for blue mold.
The fungicides Quadris and Revus are labeled for blue mold control in tobacco. Revus is applied at 8 oz/A in enough water to achieve thorough leaf coverage. Drop nozzles are highly recommended to provide coverage to lower leaves. Applications may be made 7 to 10 days apart. Make no more than 2 consecutive applications of Revus before switching to another fungicide with a different mode of activity. The pre-harvest interval for Revus is 7 days. For tobacco at topping or beyond, a single application of 8 oz/A will likely be sufficient. If conditions remain conducive for disease development younger crops may require two applications.
For crops that have not been previously treated with Quadris, a rate of 6 to 12 oz/A of Quadris may be applied in enough water to achieve thorough leaf coverage. For crops without active disease, 8 oz/A is recommended, but where the disease is already appearing 10 to 12 oz/A should be used. Drop nozzles are highly recommended to provide coverage to lower leaves. Do not make consecutive applications of Quadris. The pre-harvest interval for Quadris is 0 days, but it should be applied well before harvest to be effective in controlling the disease. For tobacco at topping or beyond, a single application of will likely be sufficient.
By Bob Pearce, Extension Tobacco Specialist, and Julie Beale, Plant Disease Diagnostician