1 / 21

Epidemiology

Epidemiology. Charcoal rot in pine seedlings. Root knot nematode in bermuda grass. Dogwood liners with powdery mildew. What is Epidemiology?. Epidemiology is the science of disease populations.

lynley
Download Presentation

Epidemiology

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Epidemiology Charcoal rot in pine seedlings Root knot nematode in bermuda grass Dogwood liners with powdery mildew

  2. What is Epidemiology? Epidemiology is the science of disease populations. Epidemiologyis the study of disease development, spread of disease and factors affecting these processes.

  3. Definitions • Epidemic – increase in disease (in a population) in time and space • Pandemic – an epidemic occurring over a large area

  4. Disease Triangle Susceptible host Favorable environment Disease causing agent

  5. Disease Pyramid Susceptible host Time Favorable environment Disease causing agent

  6. Disease Triangle + + Host Host Disease causing agent Favorable environment Time Disease

  7. Factors that affect epidemicsHost • Seedling disease – once plants are beyond 2-4 leaf stage they are no longer susceptible. • Botrytis, Penicillium, Monilinia, Septoria – plants are very resistant while young and become more susceptible as they age

  8. Factors that affect epidemicsPathogen • Level of virulence – increase in virulence means fast reproduction • Quantity of inoculum – high quantity means more chances to overwinter and more chances for initial infections

  9. Types of Inoculum • For some fungi, nematodes and parasitic seed plants – relative low levels of reproduction means epidemics take long time to get going • For some fungi and bacteria – short reproductive cycle means many generations in one growing cycle

  10. Mode of Spread Wind – propagules spread quickly Insects – can spread quickly; many km Splashing rain – severe, but local epidemic

  11. Mode of Spread Seed transmission – can be spread anywhere but epidemics depend on secondary spread or transmission Soil – usually does not cause sudden and widespread epidemics; usually local, slow spreading, but considerable severity

  12. Measurements of Disease Incidence - # or proportion of plant units diseased Severity – proportion of area or amount of tissue diseased Yield loss – proportion of yield that growers will not be able to harvest

  13. Estimation of Incidence and Yield Loss In some diseases such as cereal smuts, brown rot of stone fruit, vascular wilts of annuals, disease incidence has direct relationship on yield loss (loss of whole plant or direct loss of yield products – for example with brown rot, the peaches are destroyed) Many diseases (rust, leafspots, root lesions) – plants vary in level of disease severity and the affect of disease on yield

  14. Disease Distribution Clumped Random Regular

  15. The pattern of an epidemic can be expressed as the number of lesions, amount of diseased tissue or diseased plants. These numbers can be expressed as a curve that that shows the progress of thedisease over time. This curve is called a disease progress curve.

  16. Disease Progress Curve

  17. Type of Disease Progress Curves

  18. Simple Interest or Monomolecular Disease curve (Curve A) • Inoculum does not contribute to the epidemic during the growing season in which it was formed • Often the pathogen is a soil-borne pathogen • Example is southern blight (Sclerotiumrolfsii, brown patch)

  19. Compound Interest or Logistic Disease (Curve B) • Inoculum produced during the current epidemic is responsible for starting secondary disease cycle • Epidemics are “explosive” with logistic growth • Examples are: gray mold (Botrytis), dogwood anthracnose, stem rust of wheat

  20. Bimodal or Sigmoid Disease (Curve C) • Epidemic often affected by resistance of plant (often aging cotyledons early in season and older leaves late in season are susceptible whereas expanding leaves are resistant • Example: brown spot of soybeans (Septoria gylcines)

More Related