Fungicide modes of action for field crops - MSU Extension modes of action for field crops ... •...
Transcript of Fungicide modes of action for field crops - MSU Extension modes of action for field crops ... •...
Fungicide modes of action for field crops
Dr. Mary BurrowsMontana State University
Plant Sciences and Plant Pathology Department
Schutter Diagnostic Lab• Identify plant diseases, insects,
weeds/plants, mushrooms, toxic molds, etc. • Process approximately 2000 samples/yr
(~50% homeowner/horticulture)• Donate!
– http://msuaf.org/give-schutter_lab– 800-457-1696– Solicitation Code AG14CAGPS
http://diagnostics.montana.edu
Number of diagnoses performed at the Schutter Diagnostic Laboratory in 2016.
Number of Diagnoses
Plant Disease 2,227Insect & Spider Identification 730
Plant & Mushroom Identification 492
Herbicide Injury 65
Total 3,514
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The danger with apps and websites
• INCORRECT or Misleading information and pest identifications
• Question what the source of the information is– Public or Private– Location
Fungicides• What is a fungicide and how does it
work (conventional and organic options)?
• What does ‘MOA’ mean?• Fungicide resistance• What products are available and how do
I find them?• Economics of fungicide use
• Herbicide = ~16 classes • Insecticide = ~17 classes• Fungicide = 4-6 classes
Fungicide classes
Number of classes of common pesticides for field crops
Fungicide systemicity
• Do not penetrate into plant • Redistribute on plant
surfaces• Multi-site inhibitors• Kills spores/inhibits
germination• Protectant only• Broad spectrum
• Penetrate into plant• Redistribute on & within
plants• Single-site inhibitors• Inhibits spore germination
and or mycelial growth• Protectant and curative• Selective
Non-systemic Systemic
Single Site v. Multi-siteSystemic v. non-Systemic
• Protectant only• Can wash off• Shorter application
intervals• Broad spectrum• Low Risk of Resistance
• Protectant and curative• Less prone to washing off• Longer application
intervals• Selective• High Risk of Resistance
Non-systemic/Multi-Site Systemic/Single Site
Cell wall
Cell membrane
General cell constituents
Mitochondria
Microtubules
Nucleic acids
Specific fungicides target different sites and biochemical processes
DMI triazole fungicides
thiophanate methyl
Mefenoxam andmetalaxyl QoI (azoxy-, pyraclo-, trifloxy-, fluoxa-)
SDHI (fluxapyroxad, boscalid)
chlorothalonil
Modified from Rick Latin
Contact Strobilurins Triazoles Carboxamides
Common names Bravo, Thiram, Copper, Sulfur, oils
Stamina, Headline, Quadris…
Tilt, Folicur, Proline…
Vibrance, Boscalid, Xemium(Priaxor)…
Mode of action FRAC group M: Multiple sites of action
FRAC group 11: QoI (quinoneoutside) inhibitors (respiration); spore germination, penetration, and mycelial growth
FRAC group 3 : DMI (demethylation) inhibitors; biosynthesis of sterols in fungal cell membrane; spore penetration and mycelialgrowth
FRAC group 7: SDHI (succinate dehydrogenase inhibition; Respiration; aka carboxamides)‘new’ 2nd
generation SDHIs
Residual Low Depends on the specific product; 10-30 days
Resistance development
Low High (specific MOA)
Medium High; Practice good resistancemgmt tactics
Mobility in plant None Translaminar and systemic
High systemic activity
Carboxamide not systemic (targetslater-season applications)
Protection Contact only Protective only (kill germinating spores)
Protective and curative
Protective
Senescence Delayed Potentially delayedNote: these are generalizations about fungicide classes
TriazolesMedium Risk
StrobilurinsHigh Risk
SDHI inhibitorsHigh Risk
Group M (contact fungicides)
Low Risk
Spore germination Penetration Mycelial growthGerm tube formation Sporulation
Carboxamides Strobilurins Triazoles(SDHIs) (QoIs) (DMIs) No efficacy
Disease symptomsFungicide efficacy
Fungicide movement in the plant
From: Tenuta, A., D. Hershman, M. Draper and A. Dorrence. 2007. Using foliar fungicides to manage soybean rust.. Land-Grant Universities Cooperating NCERA-208 and OMAF. Available online at http://www.oardc.ohio-state.edu/SoyRust/
Fungicide modes of action: Strobilurins
• FRAC group 11• QoI (quinone outside) inhibitors (respiration); spore germination,
penetration, and mycelial growth• Provides 14-21 days of protection• High risk of resistance development because it has a very
specific mode of action (they block electron transfer at the site of quinol oxidation (the Qo site) in the cytochrome bc1 complex, thus preventing ATP formation)
• Originally isolated from wood-rotting fungi Strobilurus tenacellus• ‘Reduced-risk’ pesticide (pose less risk to human health than
other chemical options at the time of registration by EPA)• Control a wide array of fungal diseases• Excellent preventative fungicides, but limited curative effects• “Plant health benefit” independent of disease control?
Figure 1. Mobility of trifloxystrobin, an example of a QoI fungicide. http://www.apsnet.org/education/AdvancedPlantPath/Topics/Strobilurin/top.htm
Fungal spore with mutation that confers RESISTANCE to fungicide MOA
Fungal spore susceptible to fungicide MOA
Fungicide resistance development
Fungal spore with mutation that confers RESISTANCE to fungicide MOA
Fungal spore susceptible to fungicide MOA
When a fungal population is predominately RESISTANT to a fungicide MOA, chemical failures may occur
Fungicide resistance development
Fungicide resistance in Ascochyta blight
• 145 isolates were collected from the 2013 crop year
– 4 chickpea and 1 pea isolate were insensitive (resistant) to Headline
– One chickpea isolate was insensitive to Xemium and Boscalid– Resistance testing for Proline is ongoing
• Those seed lots were eliminated from planting• No insensitivity identified in seed from the
2014 crop year• 2015: one chickpea seed lot contained
resistant isolates, eliminated from planting• 2016: No resistant isolates identified thusfar
(11 chickpea, 42 field pea, 12 lentil seed lots)– Optimizing a real-time PCR Assay for G143A mut.
Sulfur• Ancient Greeks used against rust
disease• Powdery mildew• Prevents fungal spores from
germinating• Sulfur + oil (within a month) = phytotoxic• Lime-sulfur is a dormant spray, more
effective at lower doses but smells bad
Copper• Efficacy against fungi and bacteria• Copper sulfate + lime = Bordeaux
mixture (safener, reduces phytotoxicity)– Can persist through rain– More phytotoxic at high temperatures >85F
and if rain occurs very soon after application
• Copper especially phytotoxic on young tissue
Horticultural and neem oils• Mostly used for insects• Can minimize virus spread by piercing-
sucking insects• Can help control thrips and spread of
associated viruses (INSV, TSWV…)• Can be used to manage powdery mildew• Check phytotoxicity on plants before
widespread application• Do not apply <40F or >90F; best if RH <65%
so oil can evaporate quickly and reduce phytotoxicity
Bicarbonates• Baking soda = sodium bicarbonate• Can be effective when used with oil• Sodium can build up in soil and become
toxic to plants• Different bicarbonate salts have
different effects on plants and diseases• Ammonium and potassium bicarbonate
preferred because of added nutrients to plants and lack of sodium
MSU fungicide trials in dryland WW• 2007-2013• 35 trials• 4 reps/trial, all harvested with a
research combine• One location, one year there was a
statistically significant increase in yield with the use of a fungicide on drylandwheat in the absence of disease
Fungicide use in winter wheat NO/minimal disease, 2007-2013
Bozeman
Number of observations
(plots)Avg. Yield
(Bu/A) Havre
Number of observations
(plots)
Avg. Yield
(Bu/A)2007 15 97.2 2011 32 60.12011 28 26.0 2012 60 61.52012 200 45.2 2013 60 98.12013 66 31.1 Average 152 75.7Average 309 43.0
Hill Co. (Kremlin)Conrad 2012 60 64.72011 24 75.92012 60 83.4 Chouteau Co (Loma)Average 84 81.3 2012 104 44.1
Moccassin2013 72 36.4 Total 781 54.7
-20
-15
-10
-5
0
5
10
15
20
25
2 Bu/A
Overall, a 37% chance you will get ≥ 2 Bu/A yield increase due to fungicide
Difference in yield from the control due to fungicide (Bu/A)
Diff
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What do you notice
to be skeptical about?
Fungicide 1
Fungicide 2
Fungicide 3
Stats?How many treatments total?Location?