On June 2, active blue mold was found in a greenhouse in Greenville, Tennesee and in field plants that were set from the same greenhouse. Greenville is in eastern TN, and with recent weather systems moving south to north and conditions favorable for long distance transport of spores, there is potential for tobacco in Eastern and Central Kentucky to have been exposed to blue mold from this source. Additionally, based on initial infection occurring during May 26-28, there may be other centers of infection that have not been found yet, so other areas of Kentucky may currently have infected tobacco. Tobacco growers throughout Kentucky should closely examine tobacco float beds and fields for signs of blue mold, and rapidly report any suspected blue mold activity to their local county Extension office. Growers must remain vigilant and take steps now to protect their tobacco crops. While the threat of blue mold is formidable, growers taking a proactive approach have a number of effective, modern chemical tools to manage this threat, which are detailed below.
Any transplants remaining in float beds and greenhouses in the Commonwealth of Kentucky should be treated immediately with either Manzate Prostick or Quadris. Only one application of Quadris is allowed per season in the float bed, and this application counts toward the season limit. Plants that have been clipped but not sprayed with Quadris may be treated once with 4 cc per 1000 square feet (about 400 trays) in 4 to 5 gallons of water. Plants that have not been clipped or have already been treated with Quadris should be sprayed weekly with Manzate Prostick (1 tsp per gallon) to achieve thorough leaf coverage. Manzate is a protectant fungicide that prevents uninfected plants from new infections, and must be reapplied every 5 to 7 days for maximum effectiveness. Risk of resistance to manzate is low, yet risk of resistance to Quadris is high, so tank mixing is recommended.
Tobacco to Be Transplanted
For fields with a history of black shank pressure, growers should consider a transplant water application of the new fungicide Presidio. While no data exists at this point on Presidio’s efficacy for blue mold, it may have some activity against blue mold in fields with black shank pressure. Follow all product label instructions for application of Presidio, particularly tank mix recommendations, to maintain the effectiveness of this product. It is unknown if the blue mold in the current infection center is sensitive to mefenoxam (active ingredient in Ridomil, MetaStar, and UltraFlourish), but soil sprays of these products are described on the product labels.
Several additional products, including the azoxystrobin products Quadris, Satori, and Azoxystar, in addition to the group 40 fungicides Revus and Forum, are available to treat older tobacco transplanted in the field. Tank mixes with Manzate ProStick and rotation to fungicides with other modes of action are strongly encouraged to maintain the efficacy of these products. See 2015 Fungicide Guide for Burley and Dark Tobacco (PPFS-AG-T-8) for additional details on products labeled for control of blue mold in field tobacco.
Advice to All Kentucky Tobacco Growers
At this time growers throughout Kentucky are advised to carefully scout fields and treat with fungicides if any signs of blue mold are found.
Growers in Eastern and South Central Kentucky (Extension District 2 and the southern part of Region 5) may be considered higher risk, and should treat field tobacco with fungicides now given the potential for exposure from a known source of blue mold.
Growers in Extension Districts 1 and 4 may be considered moderate risk for blue mold, and continued scouting and field application based on the 2015 tobacco fungicide guide is encouraged if possible.
Note: Some tobacco contracts may prohibit or limit the use of Manzate in the field due to unacceptable residue levels, and Actigard should not be used on plants smaller than 18 inches. Read and follow all label directions for the use of foliar fungicides, including statements requiring tank mixes and/or alternation of products with different modes of action.
All growers should be encouraged to remain aware of the blue mold situation and be prepared to take immediate actions to protect their tobacco crops if necessary. The blue mold situation is very dynamic, and updates will continue as the extension specialists visit farms and scout for disease over the next few days.
By Bob Pearce, Extension Tobacco Specialist and Emily Pfeufer, Extension Plant Pathologist, in consultation with Andy Bailey, Extension Dark Tobacco Specialist and Kenny Seebold, Adjunct Associate Professor in Plant Pathology