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Managing tobacco blue mold in 2015: a proactive fungicide approach ANR Agents’ Special Training Emily Pfeufer1 and Bob Pearce2 University of Kentucky Departments of Plant Pathology1 and Plant and Soil Sciences2 Managing tobacco blue mold in 2015: a proactive fungicide approach • Pathogen biology and history of blue mold in KY • Fundamentals of disease management • Resistance to fungicides • Blue mold fungicide options and modes of action • Blue mold spray program Subtle yelloworange spots on tops of leaves Blue sporulation on underside of leaf Seebold, 2006 Pathogen biology • Sporangiospores are the main infectious agent • Free water on leaf surface required for germination • 5-7 days later, symptoms develop on leaves • When symptoms develop, secondary sporulation occurs • Optimal sporulation conditions: at least 1.5 hrs darkness, 95% humidity, 59 - 74°F • Peronospora tabacina, a water mold pathogen As many as 1 million spores! Modified from C.E. Main, North Carolina State University. History of blue mold in KY • Prominent disease of high density tobacco production • 1979: early blue mold confirmations and wet, cool summer resulted in over $56 million in losses in KY1 • 1980: blue mold is identified early in KY, but due to hotter, drier summer, did not result in significant losses2 • Ridomil also labeled that year for blue mold management • Resistance to Ridomil developed within 5 years of its labeling3 • Sporadic epidemics since, primarily due to poor protective sprays combined with conducive conditions • Several years with early threats, but never materialized into epidemics due to weather and/or prevention 1. Nesmith, W. C. 1984. Plant Disease 68:933-936. 2. Davis et al., 1981. Plant Disease 65:508-512. 3. Nesmith and Jones, 1984. Phytopath. 74:631. Disease management: a 3-step process Blue-gray sporulation on underside of leaf 1. Prevention – occurs prior to pathogen introduction to crop 2. Monitoring & diagnosis – scout for early, accurate disease detection Seebold, 2005 3. Cultural and chemical management – disease has already arrived, and steps are taken to reduce its impact Preventative tactics Blue mold throughout transplants In the floatbed: starting resistant varieties, regular mowing with effective clipping removal, floatbed fungicide applications Seebold, 2006 At transplant: crop rotation, preplant fertility, plant spacing, at-transplant fungicide applications In season: weed management, sucker control, fungicide applications Early lesion Palmer Resistance to fungicides Natural population of blue mold fungus in environment . . . . .. .. .. . . . .. . .. .. . . . .. . . More resistant fungi in population Fungicide application Fungicide application . .. . Fungal escapes from fungicide . . . Spores released from escapes, causing new infections ... . . . . . .. Fungal escapes Resistance to fungicides • Resistance to metalaxyl (Ridomil) in the blue mold pathogen after 5 yrs • Key to preventing development of populations with fungicide resistance is to alternate modes of action (“rotate” fungicides) • Some fungicides are more prone to resistance development than others Blue mold fungicides available today Product Active ingredient Mode of action FRAC group Actigard Acibenzolar-S-methyl Systemic acquired resistance inducer 21 Manzate ProStick Mancozeb Multi-site, contact fungicides M3 Agri-mycin 17, Ag streptomycin, Harbour Streptomycin Protein synthesis inhibitor 25 Forum, Revus Dimethomorph, Mandipropamid Inhibit cell wall formation 40 Quadris, Satori, AzoxyStar, Azoxy 2SC Strobilurin Inhibit cellular respiration 11 Presidio Fluopicolide Disrupts cell integrity 43 Mode of action – the mechanism by which a pesticide, drug, or other biologically active chemical functions (from apsnet.org) Activity of fungicides listed here • Contact fungicides (must be on plant surface prior to pathogen arrival): Manzate ProStick, streptomycin • Systemic fungicides (applied prior to arrival, but actually enter plant tissue): azoxy products, Revus, Forum, Presidio • Actigard – a different kind of systemic fungicide Bost More about Actigard Ivors and Mila • Not directly toxic to pathogen as most other fungicides are • “Primes” plant’s own defenses against infection by pathogens • Must be applied preventatively for full effectiveness • Very low risk of resistance development, no residues • KY data suggests 50% reduction in blue mold compared to untreated control, when Manzate was alternated weekly with Actigard starting 4 days post-transplant (Pearce) Blue mold fungicide program: early season • EVERYONE: Any unset floatbed plants should be treated now with either Manzate ProStick or Quadris (if not sprayed with Quadris already) • For fields with blackshank pressure, Ridomil or Presidio may be applied in setter water. No blackshank and high risk for blue mold, apply Manzate or Forum/Revus over the top • Actigard when plants are 18-inches or taller, followed by Manzate, Forum/Revus, Presidio, or azoxy product over the top • 10 days after Actigard application, reassess risk level based on regional blue mold pressure Blue mold fungicide program: late season • Continued moderate to high risk: Apply a second Actigard application followed by another fungicide spray (azoxy product, Manzate, Presidio, or Revus/Forum) • If high pressure persists or blue mold is present in field, select another fungicide to approach end of season with. Fungicide PHIs: • • • • • Azoxy products: 0 day Forum: 0 day Presidio: 7 days Revus: 7 days Manzate: 30 days Plant with systemic blue mold. Palmer Blue mold fungicides to have on-hand • Manzate ProStick (at least 2 applications’ worth) • Actigard (at least 1 app) • Azoxy compound OR Presidio (2 app) • If Presidio, apply no later than 7 d preharvest • Forum OR Revus (2 app) • If Revus, apply no later than 7 d preharvest C. Johnson, VA Tech P. Bertrand, UGA Summary • A proactive approach will minimize losses to blue mold • 6 modes of action are available to help manage blue mold • A typical grower should have 3-4 different fungicides on hand for most effective management Sporulating blue mold lesion. Seebold, 2005. Blue mold lesion on upper surface of leaf. Questions?