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Disease in tobacco crops could rise with much-needed rainfall

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By Rick Greenwell

 

The following information is from Dr. Kenny Seabold, University of Kentucky Tobacco Specialist.

The tobacco growing season in Kentucky has been marked by very dry weather, for the most part, and these conditions have not been conducive to the development of foliar diseases. As a result, there have been very few cases of target spot or frogeye to date. Another bit of good news is that blue mold appears to be nonexistent in the U.S. this year. An early outbreak of the disease in Pennsylvania was contained and no additional cases have been reported so far this season.

Recent rains have brought some much-needed moisture and we will likely see an increase in foliar diseases on tobacco around the state. Target spot and frogeye could become problematic if we begin to see regular rains. Quadris fungicide, applied at 8 fl oz/A, has been shown to give reasonably good control of target spot if applied at least once at beginning around layby. A second application may be needed at topping to help with this disease if needed, and to suppress late-season frogeye leaf spot should that disease be active. When it comes to frogeye, anecdotal evidence indicates that a rate of 10-12 fl oz/A would be more appropriate for control. Timing the Quadris applications for frogeye control should follow what we’re recommending for target spot unless disease pressure is heavy before layby. In these cases, treat with Quadris as soon as possible. A follow-up treatment may be necessary later in the season if disease is active, particularly around topping time. If multiple applications of Quadris are needed, the label requires alternation with a fungicide which has a different mode of action than Quadris. For frogeye and target spot, our only options would be Manzate Pro-Stick, Dithane DF, or Penncozeb (mancozeb fungicides). So a grower applying Quadris at layby could come back with mancozeb two to three weeks later, and then treat with Quadris either before or after layby to stay compliant with the label.

We’ve also had a few questions about tank-mixing Quadris with other products. The Quadris label states that this fungicide should never be mixed with pesticides formulated as emulsifiable concentrates (ECs), or those that have high solvent levels, to avoid the risk of severe phytotoxicity (leaf burn, mainly). I’ve also heard from contacts at Syngenta that products such as maleic hydrazide (MH), foliar fungicides, and even acephate (Orthene or generic formulations) also increase the risk of crop injury if mixed with Quadris. I recommend that Quadris never be applied with any sucker control material, foliar fertilizer, or surfactant. With regard to Orthene, we have had some reports of injury in Kentucky when this insecticide is tank-mixed with Quadris; however, many have applied this combination with no ill effects. To play it safe, it may be best to not use Orthene and Quadris together during the hot, dry spell that we’re under right now. Quadris can cause weather flecking if applied by itself in hot weather, and would be more likely to burn if tank-mixed with Orthene under these conditions.

Dr. Donna Amaral-Phillips has informed us about the Kentucky Department of Agriculture and the Kentucky Livestock Care Stands Commission are inviting the public to an open forum on farm animal care. The Commission is currently drafting new rules for livestock and poultry care. Both written and oral comments will be accepted by the Commission.  

This will be held on Monday, July 30 from 1-3 p.m. in the State Capitol Annex, Room 129, 700 Capitol Avenue, Frankfort, Ky.