Fungicide modes of action for field crops

Dr. Mary BurrowsMontana State University

Plant Sciences and Plant Pathology Department

What do I need to do BEFORE deciding a fungicide

application is necessary?

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

The good

The ugly

Sign up for a FREE account to receive sugarcane aphid

alerts and notifications when it has been detected near you!

Visit https://www.myfields.info/sca to learn more!

c. Wendy Johnson, KSU

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

http://archives.eppo.int/MEETINGS/2010_conferences/septoria/06_Leadbeater.pdf

http://archives.eppo.int/MEETINGS/2010_conferences/septoria/06_Leadbeater.pdf

Compare sprayed and unsprayed plots

Control (no fungicide), 14 daa

Strobilurin fungicides, 14 daa

Headline

Gem 500 SC

Strobiliurin + Trizole, 14 daaQuilt

Quilt Xcel

Strobiliurin + Trizole, 14 daa

Prosaro

Twinline

Trizole fungicides, 14 daa

Alto

Proline

Caramba

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.

Organic fungicides

https://www.extension.purdue.edu/extmedia/bp/bp-69-w.pdf

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

Biocontrols

http://www.apsnet.org/edcenter/advanced/topics/Pages/BiologicalControl.aspx

c. R. Sisco, UC-Davis WRIR4

45 products for wheat23 Jan, 2017

• 2 on dry pea; 6 on chickpea; 66 alfalfa

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)

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https://www.msuextension.org/econtools/fungicide/index.html

What do you notice

to be skeptical about?

Fungicide 1

Fungicide 2

Fungicide 3

Stats?How many treatments total?Location?