Managing

tobacco blue mold

in 2015:

a proacti

ve fungici

de approa

chANR Agents’ Special Training

Emily Pfeufer1 and Bob Pearce2

University of KentuckyDepartments 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 Seebold, 2006

Subtle yellow-orange spots on tops of leaves

Blue sporulation on underside of leaf

Pathogen biology

Modified from C.E. Main, North Carolina State University.

• Peronospora tabacina, a water mold pathogen

• 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

As many as 1 million spores!

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

1. Prevention – occurs prior to pathogen introduction to crop

2. Monitoring & diagnosis – scout for early, accurate disease detection

3. Cultural and chemical management – disease has already arrived, and steps are taken to reduce its impact

Seebold, 2005

Blue-gray sporulation on underside of leaf

Preventative tacticsIn the floatbed: starting resistant varieties, regular mowing with effective clipping removal, floatbed fungicide applications

At transplant: crop rotation, preplant fertility, plant spacing, at-transplant fungicide applications

In season: weed management, sucker control, fungicide applications

Blue mold throughout transplants

Seebold, 2006

PalmerEarly lesion

Resistance to fungicides

..... ....

.. .

Natural population of blue mold fungus in environment

Fungicide application .

. .

Fungal escapes from fungicide

.. ... .. ...

Spores released from escapes, causing new infections

Fungicide application

.. ..

More resistant fungi in population

.. ... ....

. . .. .

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 todayProduct 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

• 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

More about Actigard

Ivors and Mila

• 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?