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Fungicide Resistance: Can it be Prevented?
1. Fungicide Resistance: Can it be prevented?
Lane P. Tredway
Associate Professor and Extension Specialist
Department of Plant Pathology
North Carolina State University
2. What is fungicide
resistance?
• an evolutionary process, ‘natural
selection’
• a pathogen is a population of
individuals
• some may be naturally resistant to a
given fungicide
• if that fungicide is used repeatedly, the
resistant strains become dominant in
the population
• control failure occurs
3. Fungicide Resistance: Survival of the Fittest
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4. Fungicide Resistance: Survival of the Fittest
• a small portion of the population x x
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has natural, genetic resistance to x x x x x x x x
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a given fungicide x
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5. Fungicide Resistance: Survival of the Fittest
• a small portion of the population x x x x x
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has natural, genetic resistance to x x x x x x x
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a given fungicide x
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• when that fungicide is applied, x x x x x x x x x x x
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the resistant strains increase in x
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the population x x x x x x x x x x x
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6. Fungicide Resistance: Survival of the Fittest
• a small portion of the population x x
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has natural, genetic resistance to x x x x x x x x
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a given fungicide x
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• when that fungicide is applied, x x x x x x x x x x x
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the resistant strains increase in x
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the population x x x x x x x x x x x
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• when the resistant strains x x
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become dominant, control failure x
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occurs x x x x x x x x x
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7. Fungicide Resistance: Survival of the Fittest
• a small portion of the population
has natural, genetic resistance to
a given fungicide
• when that fungicide is applied,
the resistant strains increase in
the population
• when the resistant strains
become dominant, control failure
occurs
9. FRAC codes are displayed prominently on new fungicide labels
10. Cross Resistance and Multiple Resistance
Cross Resistance
Untreated a
• resistance is specific to a
Disarm ab chemical class
Insignia ab • if a pathogen becomes
resistant to azoxystrobin, it
Heritage a will also be resistant to
fluoxastrobin, pyraclostrobin,
Signature + Daconil b and trifloxystrobin (all QoI
0 7.5 15 22.5 30 fungicides)
Anthracnose Incidence
11. Sclerotinia homoeocarpa
Cross Resistance and
Multiple Resistance
Multiple Resistance
• pathogens may develop thiophanate-methyl propiconazole iprodione
resistance to more than
one chemical class Colletotrichum graminicola
• each resistance evolves
independently of the pyraclostrobin azoxystrobin
Unamended
others
0.003 ppm 0.031 ppm
thiophanate- pyraclostrobin azoxystrobin
methyl 0.8 ppm 8 ppm
10 ppm
13. Fungicide Resistance: Current Status
Dollar Spot
• resistance to benzimidazoles
widespread
• reduced sensitivity to DMIs is
common, but to varying degrees
• dicarboxamide resistance is rare
14. Fungicide Resistance: Current Status
Dollar Spot
• resistance to benzimidazoles
widespread
• reduced sensitivity to DMIs is
common, but to varying degrees
• dicarboxamide resistance is rare
Anthracnose
• nearly all populations are resistant
to QoIs and benzimidazoles
• some are partially sensitive
15. Resistance Case Studies: Benzimidazoles
• single mutation in pathogen
• complete control failure
• develops quickly
• resistant strains persist
indefinitely
16. Resistance Case
Studies: DMIs
• multiple mutations in pathogen
• gradual reduction in population
sensitivity over time
• appears as a gradual reduction
in control efficacy or residual
• strains may not persist in
absence of DMI applications
56. What can we learn from the medical field?
How can antibiotic resistance be
prevented?
• maintain healthy lifestyle to
minimize reliance on antibiotics
• sanitation
• diagnose illnesses acurately
• avoid repetitive use of same
antibiotics
• mix antibiotics when necessary
57. Preventing Fungicide
Resistance
• maintain healthy turf
• employ IPM strategies
• diagnose diseases accurately
• avoid repetitive use of high-risk
chemical classes
• tank-mix in high-risk situations
59. High Risk Medium Risk Low Risk
Turfgrass pathogens vary in their ability to develop fungicide
resistance.
60. High Risk Medium Risk Low Risk
Fungicides also vary in their susceptibility to fungicide resistance.
61. What determines the resistance risk?
• pathogens vary in their
ability to evolve
resistance
• fungicides vary in their
susceptibility to
resistance
• resistance risk is
determined by the target
pathogen and selected
fungicide
62. Calculating the Resistance Risk
-----Pathogen Resistance
Risk-----
• each pathogen is
---Fungicide Resistance Risk---
Low Risk (1) Med. Risk (2) High Risk (3)
assigned a risk value
Low Risk (1) 1 2 3
• each fungicide is
assigned a risk value
Med. Risk (2) 2 4 6
• multiply them together
High Risk (3) 3 6 9 to identify the
recommended strategy
63. Resistance Risk Determines the Best Strategy
Resistance
Risk Recommended Action
Rotate to different chemical class after EVERY application; Tank-
9
mix with low or moderate risk product for EVERY application
Rotate to different chemical class after 1-2 applications; Tank-
6
mixing with low or moderate risk product recommended
Rotate to different chemical class after 1-2 applications; Tank-
4
mixing not necessary
Rotate to different chemical class after 2-3 applications; Tank-
3
mixing not necessary
Rotate to different chemical class after 3-4 applications; Tank-
2
mixing not necessary
Rotating and tank-mixing not necessary, but recommended to avoid
1
potential side affects from continuous use of same chemical class