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Managing Fungicide Resistance

Managing Fungicide Resistance. Anne DeMarsay Maryland Wine & Grape Industry Meeting February 28, 2009. Fungicide Resistance 101. What Is Fungicide Resistance?. Resistance = a stable, heritable trait that results in a reduction in sensitivity to a fungicide by an individual fungus

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Managing Fungicide Resistance

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  1. Managing Fungicide Resistance Anne DeMarsay Maryland Wine & Grape Industry Meeting February 28, 2009

  2. Fungicide Resistance 101

  3. What Is Fungicide Resistance? • Resistance = a stable, heritable trait that results in a reduction in sensitivity to a fungicide by an individual fungus • Practical resistance = labeled rates of a fungicide no longer provide commercially acceptable control of a disease

  4. Why Monitor Resistance? • Resistance  control failures  crop losses • Use of ineffective fungicides may increase resistant strains of fungi

  5. How Does Resistance Occur? • Origin: rare genetic mutation(s) that alter the target site in the fungus to block the action of the fungicide • Natural selection: fungicide causes selection of the fittest (resistant) individuals

  6. Fungicides select resistant individuals A. B. Baudoin, VPI & SU

  7. After the fungicide “wears off”... A. B. Baudoin, VPI & SU

  8. How Does Resistance Occur? • Origin: rare genetic mutations that alter the target site(s) in the fungus to block the action of the fungicide • Natural selection: fungicide causes selection of the fittest (resistant) individuals • Resistant individuals are more likely to survive to reproduce • When the fungus reproduces, resistant individuals pass on the mutation

  9. Types of Resistance • Qualitative resistance: sudden loss of control • Resistance results from a single mutation in one gene • Quantitative resistance: gradual reduction in control • Resistance results from mutations in several genes that interact

  10. Target site mutation Stepwise, small changes One-step, large changes A. B. Baudoin, VPI & SU

  11. Resistance to More Than One Fungicide • Cross resistance: when a pathogen resistant to one fungicide exhibits resistance to other fungicides in the same chemical class, even without exposure • Multiple resistance: when a pathogen independently develops resistance to fungicides in different chemical classes

  12. What Fungicides Are at Risk?

  13. Penetrant Systemic Fungicide categories A. B. Baudoin, VPI & SU Protectant

  14. Protectant fungicides tend to... have a multi-site mode of action have few problems with resistant strains of target fungi Penetrant fungicides tend to... have a single-site mode of action allow target fungi to develop strains with resistance to the fungicide (risk varies) Contrasts: protectant vs. penetrant A. B. Baudoin, VPI & SU

  15. Multi-site inhibitor A. B. Baudoin, VPI & SU

  16. Protectants cannot penetrate plant tissue A. B. Baudoin, VPI & SU Cuticle

  17. Penetrants and systemics DO penetrate plant tissue. Target site differs: single-site Cuticle A. B. Baudoin, VPI & SU

  18. Fungicides at Risk • Most newer fungicides are single-site inhibitors (penetrant or systemic) • Single-site inhibitors are more prone to resistance development (qualitative and quantitative)

  19. Single-site inhibitors are much more prone to resistance development than multi-site inhibitors • Fungicide and its target site • Characteristics of target fungus and disease HOW much more?Depends on... A. B. Baudoin, VPI & SU

  20. HOW much more? Factor #1: fungicide and target site • Nature of target site, how essential? • Nature of changes possible • How easily does site mutate? • Are changes detrimental to organism? A. B. Baudoin, VPI & SU

  21. Factor #2: Characteristics of target fungus and disease • How fast does fungus reproduce? • How easily does it spread? • How much variability in population? A. B. Baudoin, VPI & SU H. Couch J. Verreet

  22. Fungicide/target site risk A. B. Baudoin, VPI & SU Hot zone! High Benzimidazoles Strobilurins Mancozeb Chlorothalonil Powdery mildew Rhizoctonia Low Pathogen risk Low High

  23. Fungicide Resistance: Two Case Studies

  24. Case #1: Strobilurins (QoIs) • Used to control grape powdery mildew (PM) and grape downy mildew (DM) • First sold in 1996; in widespread use by 1998 • Azoxystrobin (Abound) labeled for grapes in 1997 • Others introduced between 2001 and 2008 • High risk of resistance development • Mode of action: single-site inhibitor of energy production in fungal mitochondria • Qualitative resistance (one mutation): sudden • Cross resistance among all strobilurins

  25. Case #1: Strobilurins (QoIs) • Resistant grape PM strains detected • In NY and PA in 2002 (1st cases in U.S.) • In VA, MD, NC, and PA in 2005–07 • In Europe in 2006 • Resistant grape DM strains detected • In Europe in 2000 • In VA in 2005 (1st case in U.S.) • In MD, NC, and PA in 2005–07

  26. QoI sensitive Majority QoI resistant JW AV HC WF Li Vi MR LV Re CR PR Su GR IV Be AM CO Bx RO GL JR NK BR B Ar CM MV SP Ha Sh SC Powdery mildew Map: J. F Colcol, A. B. Baudoin

  27. QoI sensitive Majority QoI resistant Map: J. F Colcol, A. B. Baudoin

  28. Case #1: Strobilurins (QoIs) • When resistance was first detected in Virginia • Vineyards with resistant PM/DM had been sprayed from 0 to 17 times with strobilurins • Sprays per season averaged 2 to 3.4 • FRAC recommends 3 sprays max. per year; labels allow 4 sprays • Current resistance management guidelines not adequate to prevent RAPID development of resistance

  29. Case #2: Sterol Biosynthesis Inhibitors (SBIs) • In use since 1982 for grape PM • 1982: triadimefon (Bayleton) • 1989: fenarimol (Rubigan), myclobutanil (Nova/Rally) • 1990s: tebuconazole (Elite), triflumizole (Procure) • Medium risk of resistance • Mode of action: single-site inhibitor of ergosterol synthesis • Quantitative resistance (several mutations in interacting genes): gradual loss of sensitivity • Partial cross resistance

  30. Case #2: Sterol Biosynthesis Inhibitors (SBIs) • Loss of sensitivity in grape PM strains detected • In CA in 1985–86 (triadimefon) • In NY in 1995 (triadimefon, fenarimol, myclobutanil) • In Canada in 1999–2000 (myclobutanil) • In VA, MD, NC, and PA in 2005–07 (triadimefon, fenarimol, myclobutanil, tebuconazole, triflumizole)

  31. Case #2: Sterol Biosynthesis Inhibitors (SBIs) • Mid-Atlantic samples of grape PM • Greater loss of sensitivity to myclobutanil (Nova/Rally) and tebuconazole (Elite) than other SBIs • Multiple resistance: isolates that were resistant to strobilurins were more resistant to SBIs • A possible reason: correlated selection pressure

  32. Case #2: Sterol Biosynthesis Inhibitors (SBIs) • Spray history at Upper Marlboro, MD farm • Vineyard planted in 2001 • Reduced sensitivity to SBIs detected in 2006 • Myclobutanil (Nova) applied 11 times 2003–07 • Sprays per season: 1 or 2; once 3 • FRAC recommends 4 sprays max. per year; Nova/Rally label allows ~5 sprays • Current resistance management guidelines not adequate to prevent loss of sensitivity

  33. Managing Resistance

  34. Other Reasons for Control Failures • Poor timing • Starting protectant applications too late • Spray intervals too long • Missed sprays • Spotty coverage • Sprayer not calibrated or nozzles not adjusted • Inadequate spray volume for canopy

  35. Coverage A. B. Baudoin, VPI & SU Variable More uniform

  36. Other Reasons for Control Failures • Wrong rate of fungicide • Rate too low for the disease—read the label! • In a tank mix, use at least the minimum rate on the label for each fungicide • Canopy too dense • Too windy during spraying

  37. Delaying Resistance Development • Practice integrated disease management • Plant disease-resistant varieties • Use cultural controls first (good canopy management, sanitation) • Use protectant fungicides to prevent disease buildup • Spray effectively • Calibrate your sprayer every year. Check coverage with water-sensitive spray cards • Use appropriate spray intervals and volume for the fungicide and time of the season

  38. Good coverage Area of poor coverage A. B. Baudoin, VPI & SU

  39. After the fungicide “wears off”... A. B. Baudoin, VPI & SU Poor coverage Better coverage

  40. Delaying Resistance Development • Plan your spray program • Limit the number of applications of high- and medium-risk fungicides • Use the right rate for the disease • Rotate among different classes of fungicides • Tank-mix fungicides from different classes that are effective against the same disease • Add 2–5 lb sulfur to a strobilurin or SBI spray for powdery mildew • Add captan or a phosphorous acid to Pristine for downy mildew

  41. Summary • Resistance is the evolutionary response of a fungus to a threat to its survival: the fungicide • Fungicides that act at a single site are more prone to resistance development • How quickly resistance will develop, and how much control will be lost, depend on both the fungicide and the target fungus • Resistance to most newer fungicides will occur, but we can prolong their effective life by careful use

  42. Any Questions?

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