Characterization of Propiconazole Movement and Survival of Ceratocystis fagacearum in Oak Roots

Transcription

1 Characterization of Propiconazole Movement and Survival of Ceratocystis fagacearum in Oak Roots Interactions between Host, Pathogen, and Systemic Fungicides Upper Midwest Invasive Species Conference October 30, 2012 Ryan Blaedow Forest Health Specialist Minnesota Department of Natural Resources Jennifer Juzwik Research Plant Pathologist USDA Forest Service, Northern Research Station

2 D. W. French, University of Minnesota, Bugwood.org Oak Wilt Introduction Pathogen spread occurs via two mechanisms Overland via insect vectors Below-ground via root grafts James Solomon, USDA Forest Service, Bugwood.org

3 Oak Wilt Introduction Integrated Management Strategy Inoculum reduction and wound prevention Root graft barriers and systemic fungicides Joseph O'Brien, USDA Forest Service, Bugwood.org Joseph O'Brien, USDA Forest Service, Bugwood.org J. Juzwik J. Juzwik

4 Propiconazole A Systemic Fungicide Propiconazole has been used for oak wilt control since 1980 s Intravascular injections Fungicide distributed in transpiration stream Treatment Efficacy Increasingly important method of disease control Very good control for two years Retreatment on a biannual basis is necessary Many questions remain Joseph O'Brien, USDA Forest Service, Bugwood.org

5 Preventative Treatments Do they prevent root graft transmission? How frequently will re-treatment be necessary?

6 Some downward movement of systemic fungicides can be expected Can propiconazole prevent root graft transmission? Is eradication of the pathogen from the roots possible? Extent of translocation into roots Fungicidal, fungistatic, or neither in vivo Pathogen survival in treated trees

7 Implications of the Distribution of Propiconazole on the Management of Below-Ground Spread of Ceratocystis fagacearum Objectives Phytopathology 100: , Sept 2010 Determine if propiconazole moves into the root system following injection Determine if C. fagacearum can survive in the roots of treated trees Determine if propiconazole can prevent infection / eradicate the pathogen in the root system Approach Root-inoculate propiconazole treated trees with C. fagacearum Assess presence of the fungicide and pathogen in the root system over time

8 Materials and Methods 4 Treatments, 6 trees selected per treatment Preventative: injected with propiconazole then inoculated two weeks later with C. fagacearum Therapeutic: inoculated with C. fagacearum then treated two weeks later with propiconazole Disease control: inoculated with C. fagacearum and injected with water Fungicide Control: injected with propiconazole and simulated inoculation with sterilized water

9 Propiconazole Application Materials and Methods Macroinfusion method 20 ml Alamo (14.3% AI) in 1 L water per 2.5 cm DBH 1.5 injection tees per 2.5 cm dbh, inserted at root flares J. Juzwik

10 Materials and Methods Root inoculations Three roots per tree excavated with an Airspade Hole drilled in each root 1.0 m from injection point 1.0 ml spore suspension (106 spores ml-1) Hole sealed with epoxy putty and parafilm Roots covered with sand to original grade

11 Sampling Materials and Methods Roots sampled sub-sampled 2 months, at m year, intervals or 2 years after treatment One samples taken from stem 0.33m above each injection Two point trees evaluated in each plot per sampling period Three Assessed inoculated for presence roots of removed pathogen from and each fungicide tree Inoculation Point Injection Points

12 Materials and Methods Pathogen Assay: standard isolation protocol Plated onto lactic acid-amended PDA, incubated at 25ºC for 30 days Second attempt to isolate was conducted if first attempt was negative Fungicide Assay: Microwave extraction and GCMS Data analysis: SAS 9.1.3; PROC MIXED

13 Results Propiconazole Assays Propiconazole was detected in the roots/stem of all treated trees At all distances from the injection point At all sampling time periods, including 24 months Pattern of fungicide distribution did not differ between fungicide control, therapeutically-treated, or prophylactically-treated trees (P=0.7729)

14 Propiconazole concentrations (ppm) in a treated tree two months after treatment Injection Sites Injected solution = 3050 ppm

15 Results Propiconazole Distribution in Treated Oaks Propiconazole concentration decreased with increasing distance from the injection point (P<0.0001) Propiconazole Concentration (ppm) A B C Injection Point B CD Distance From Injection Point (m) C DE F F 2 Months 12 Months 24 Months E G G

16 Results Propiconazole Distribution in Treated Oaks Propiconazole concentration decreased over time (P<0.0001) 500 PPZL at -1m A PPZL at -0.66m PPZL at -0.33m PPZL at +0.33m PPZL Concentration (ppm) B CD B C C DE 0 E F F G G Months After Treatment

17 Results C. fagacearum Distribution in Disease Control Oaks Disease Development Symptoms appeared within 4 weeks Completely wilted after 8 weeks Pathogen incidence decreased over time (P=0.0072)

18 Results C. fagacearum Distribution in Disease Control Oaks 2 Months Pathogen Incidence in Disease Control Wood Samples 1.0 A A A A A A AB m m m m Pathogen Incidence B B 0.2 BC Months After Treatment C C

19 Results C. fagacearum Distribution in Disease Control Oaks 12 Months Pathogen Incidence in Disease Control Wood Samples 1.0 A A A A A A AB m m m m Pathogen Incidence B B 0.2 BC Months After Treatment C C

20 Results C. fagacearum Distribution in Disease Control Oaks 24 Months Pathogen Incidence in Disease Control Wood Samples 1.0 A A A A A A AB m m m m Pathogen Incidence B B 0.2 BC Months After Treatment C C

21 Results C. fagacearum Distribution in Propiconazole-Treated Oaks 2 Months m m m m Pathogen Incidence ABC AB ABC A ABC 0.2 CD CD 0.0 D D D D D Months After Treatment

22 Results C. fagacearum Distribution in Propiconazole-Treated Oaks 12 Months m m m m Pathogen Incidence ABC AB ABC A ABC 0.2 CD CD 0.0 D D D D D Months After Treatment

23 Results C. fagacearum Distribution in Propiconazole-Treated Oaks 24 Months m m m m Pathogen Incidence ABC AB ABC A ABC 0.2 CD CD 0.0 D D D D D Months After Treatment

24 Results C. fagacearum Distribution in Treated Oaks Disease Development No disease development during 2 year study Two trees (prophylactically treated) wilted 35 months after treatment Propiconazole effects on C. fagacearum distribution No treated trees were free of the pathogen at any time 53% of roots yielded C. fagacearum (n=34) Treatments did not prevent infection Treatments did not eradicate the pathogen No difference in pathogen incidence or distribution between prophylactically and therapeutically treated oaks (data not shown)

25 Results Effect of Propiconazole Concentration on C. fagacearum Propiconazole strongly concentration suppressed had no pathogen effect on incidence pathogen in treated incidence trees 24 months after 2 and after 12 treatment months (P=0.0016, (P=0.0305) 0.009)

26 Discussion Propiconazole Distribution in Oaks Propiconazole does move into the root system after injection Mechanism for movement unknown Phloem mobility or positive pressure from injection tank Concentration decreases with increasing distance Extent of fungicide distribution is limited Prevention of root graft transmission unlikely Concentration decreases over time Rate of degradation lower in roots than above ground Significant concentrations remain after 24 months

27 Discussion Propiconazole Effects on C. fagacearum Propiconazole cannot prevent infection/eradicate C. fagacearum Fungitoxic concentrations are higher in vivo than in vitro C. fagacearum confined to root system for 12 months Propiconazole efficacy drops after 24 months Compartmentalization of fungicide, not pathogen

28 Discussion Propiconazole Effects on C. fagacearum C. fagacearum was never isolated at m in treated trees Difference in arrangement of vascular elements Less continuous, more interconnected Allows translocation of fungicide, slows pathogen movement

29 Conclusions Propiconazole suppresses disease development Longevity of effects extended by residual fungicide in root crown and lower stem Treatment efficacy not affected by timing of fungicide application in relation to infection Retreatment will be necessary, though the number of retreatments is unknown Propiconazole can induce latent infections, treated trees are potential inoculum sources

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