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Plant Disease Epidemiology

Epidemic: disease increase in a population. Epidemic development is influenced by:. Environmental factorsRate of pathogen reproductionMode of pathogen dispersalEfficiency of pathogen survivalLevel of aggressiveness of the pathogenLevel of host plant resistance . What is epidemiology used for?.

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Plant Disease Epidemiology

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    1. Plant Disease Epidemiology --03-3 Disease Epidemic

    2. Epidemic: disease increase in a population

    3. Epidemic development is influenced by: Environmental factors Rate of pathogen reproduction Mode of pathogen dispersal Efficiency of pathogen survival Level of aggressiveness of the pathogen Level of host plant resistance

    4. What is epidemiology used for? 1 – Model disease progress

    5. A monocyclic pathogen completes just one disease cycle per season. There are no secondary disease cycles. Can you think of some examples of monocyclic pathogens?

    6. Soilborne pathogens are usually monocyclic due to physical constraints--inoculum is not dispersed within the growing season.

    7. Some rust and smut fungi are monocyclic because their life cycles take a full season to complete.

    8. Polycyclic pathogens have several secondary disease cycles each season.

    9. Disease increase in plant populations is sometimes compared to the increase of invested capital over time. Diseases caused by monocyclic pathogens are analogous to investment with simple interest; diseases caused by polycyclic pathogens are analogous to investment with compound interest.

    10. With simple interest, capital grows at a constant rate (the interest bearing capital remains unchanged)

    11. With compound interest, invested capital grows at an increasing rate over time as the earned interest is reinvested.

    12. The mathematical formula describing increase of capital at continuous compound interest is the same formula used in biology to describe exponential growth. The formula can also be applied to epidemics caused by polycyclic pathogens.

    13. Exponential Disease Increase Compound-interest Disease Polycyclic Pathogen

    15. In reality, polycyclic diseases increase exponentially only during the very early stages of an epidemic (< 5% disease). Why do you think this is so?

    16. Reasons why disease does not increase exponentially for long: As the amount of healthy tissue becomes limiting, the rate of disease increase slows down. Infection occurs intermittently, not continuously. Newly infected tissue is not immediately infectious. Disease tends to occur in foci, not evenly throughout the field.

    17. Disease progress curve for a typical polycyclic pathogen is an S-shaped curve.

    18. Logistic Growth Compound-interest Disease Polycyclic Pathogen

    19. Disease progress curve for a typical monocyclic pathogen

    20. Mathematical model for monocyclic diseases

    21. What is epidemiology used for? 1 – Model disease progress 2 – Assess effectiveness of alternative control measures

    22. Progress of late blight in plots of susceptible (Hudson) and resistant (Sebago) potatoes.

    23. Effect of different fungicide dosages on development of potato late blight. (Cultivar Russet Rural; weekly applications in kg/ha.)

    24. Effect of different levels of weekly fungicide applications on Late Blight epidemics in plots of Russet Rural and Sebago potatoes.

    25. Effects of fungicide dose on yield of Sebago and Russet Rural potatoes under conditions favorable for Late Blight.

    26. The cultivar with a higher level of general resistance requires less fungicide to produce an acceptable yield. If weekly applications of 1.75 kg/ha gave adequate control with Russet Rural, we could expect that 1.50 kg/ha would be sufficient for Sebago.

    27. Example: How much lettuce mosaic virus infection can be tolerated in lettuce seed lots? r = 0.12 per day Season is 70 days long 1% infection tolerated in crop at harvest

    28. Lettuce mosaic virus seed assay (cont.)

    29. Any disease management practice is aimed at doing one of three things: Reducing the amount of initial inoculum (X0) Reducing the infection rate (r) Reducing the time disease is allowed to develop (t)

    30. Choose a typical polycyclic disease Describe a disease management strategy which will reduce the amount of initial inoculum. Describe a disease management strategy which will reduce the rate at which disease develops. Determine how each of these management strategies will affect the disease progress curve.

    32. What is epidemiology used for? 1 – Model disease progress 2 – Assess effectiveness of alternative control measures 3 – Predict disease spread

    35. What is epidemiology used for? 1 – Model disease progress 2 – Assess effectiveness of alternative control measures 3 – Predict disease spread 4 – Predict yield loss

    37. What is epidemiology used for? 1 – Model disease progress 2 – Assess effectiveness of alternative control measures 3 – Predict disease spread 4 – Predict yield loss 5 – Disease forecasting

    38. Relationship of temperature and duration of leaf wetness to infection by ascospores of Venturia inequalis

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