Epidemiology

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1. Define Epidemiology
• upon the population
• science of disease in populations
2. Define Epidemic
• change in disease intensity in
• a host population over time and space
3. what makes up the epidemic pyramid
• With epidemic in the center:
• Host
• Time and space
• pathogen
• environment
4. What is an Incidence?
Proportion of infected or diseased plants
5. What is the severity of a disease?
• Proportion of symptomatic tissues in
• infected plants
6. What do we do with disease intensity data?
• Describe, compare and predict epidemics:
• over time & space
• estimate impacts on yield
• under different management regimes
7. What does AUDPC stand for?
• Area under the disease
• progress curve
8. How can we use disease curves
• Describe diseases over time and space
• • Monitor response of disease to control
• measures
• • Use data to build models to estimate
• parameters, trends, & predict epidemics
• • Use data to test hypotheses about
• effects of management on disease
9. What factors influence disease?
• Initial inoculum = X0
• Rate constant =R
• Time = T
10. Why use disease progress curves?
• • Compare control measures
• • Compare effect of environment on disease development
• • Predict future disease development
• • Disease forecasting for improved control
11. What causes Mummyberry on blueberry
Monilinia vaccinii-corymbosi
12. Modeling Polycyclic Epidemics
• X = X0e^rt
• Modeling Polycyclic Epidemics
• • X = disease at time t
• • X0= initial inoculum
• • r = rate of disease increase
• • t = time
• • e = base of natural log
13. Compare the equations for the two types of disease cycles
• Monocyclic Model X = XORt
• Polycyclic Model: X = XOe^rt
14. What  are 3 ways in which we
can reduce X at any point in the
epidemic:
• 1) Reduce the initial inoculum XO
• 2) Reduce the rate of infection (R in the monocyclic model and r in
• the polycyclic model)
• 3) Reduce the duration of the epidemic (the time, t, at the end of
• the epidemic)
15. What is X0 composed of?
• X0 depends upon:
• • inoculum from previous crops within a field
• • inoculum from crops in adjacent fields
16. How is the initial inoculum (XO) reduced?
• destroying infested plant debris
• • removing diseased plants
• • chemical seed treatments
• • protective fungicides
• • race-specific disease resistance
• • biological control agents targeted
• at initial inoculum
17. What causes Mummyberry on blueberry?
Monilinia vaccinii-corymbosi
18. How to manage Monilinia vaccinii-corymbosi
• Bury mummified berries
• Mulching to cover mummies
• Disruption of apothecia development in spring bycultivation or raking
• Use resistant cultivars
• Manual removal
• Application of fungicide to developing apothecia
19. What is R composed of?
• r depends upon
• reproductive potential of the pathogen
• virulence of the pathogen
• susceptibility of the host
• conduciveness of environment
20. WHat do you need to get Mummyberry disease?
• susceptible flower buds and leaves
• rain and fog
• mummyberry apothecia producing spores
• higher temps cause the spores to germinate faster
21. what reduces r?
• r is affected by:
• non-specific disease resistance or “ratereducingresistance”
• systemic fungicides
• cultural practices that alter environment
• removal of diseased plants
22. Disease Control Effect of Reduction in Primary Inoculum and Rate of Disease Increase
Conclusion: Reducing initial inoculum forpolycyclic epidemics only effective whenrate of disease increase is low
23. How do humans affect the susceptibility of plants to disease?
24. How do humans affect the susceptibility of plants to disease?
• Introduced Plants
• many crop plants are grown far from their native range
• pathogens in area of introduction may jump to new host that lacks resistance
• Genetic Uniformity- large populations of genetically identical plants
• uniform ripening times, uniform processing qualities,facilitate single harvesting operation
• creates conditions for large-scale epidemics (eg. potatolate blight, Southern corn leaf blight).
• Monoculture
• planting pure stands of a crop plant higher density plantings = more disease
25. How do humans affect the environment to favor plant disease?
• Water Management
• timing of irrigation – morning versus evening?