Plant disease epidemiology is the quantitative study of disease spread in plant populations, incorporating biological, statistical, agronomic, and ecological perspectives. It involves modeling and understanding factors influencing disease spread over time and space. While rooted in efforts to control plant disease, it now extends to predicting the impact of climate change on diseases like rice leaf blast, oak disease, grape downy mildew, and various forest diseases using weather data from climate change models.

1. Role of Epidemiology in
Plant Disease Management
Submitted by :-
Aishna Srivastava M.Sc. Plant Pathology IARIKAR20232011

2. Introduction to Plant Disease Epidemiology
Plant disease epidemiology is the quantitative study of disease spread in
plant populations, incorporating biological, statistical, agronomic, and
ecological perspectives. It involves modeling and understanding factors
influencing disease spread over time and space. While rooted in efforts to
control plant disease, it now extends to predicting the impact of climate
change on diseases like rice leaf blast, oak disease, grape downy mildew, and
various forest diseases using weather data from climate change models.

3. Plant disease epidemics are categorized into Monocyclic
and Polycyclic types based on the number of infection
cycles per crop cycle
 Monocyclic epidemics follow a linear model in
their early stages.
 These epidemics involve one infection cycle per
crop cycle.
 Early stages of monocyclic epidemics can be
described using a linear model.
 To reduce disease levels in monocyclic
epidemics:
 Reduce the initial inoculum (Q), which is
proportional to the initial disease incidence.
 This can help limit the spread of the
disease.
 Polycyclic epidemics exhibit an exponential
model.
 Polycyclic epidemics have multiple infection
cycles during a crop cycle.
 Early stages of polycyclic epidemics can be
described using an exponential model.
 Strategies to reduce disease levels in polycyclic
epidemics include:
 Lowering the rate of infection (R or r).
 Shortening the duration of the epidemic
(t).
Monocyclic epidemics Polycyclic epidemics

4. Using Traditional Principles
Tactics for the Reduction of Initial Inoculum and Infection rates
 Avoidance: Reduce the rate of production of inoculum, the rate of infection, or the rate of development of the
pathogen by selecting a season or a site where the environment is not favorable.
 Exclusion: Reduce the introduction of inoculum from external sources during the course of the epidemic.
 Eradication: Reduce the rate of inoculum production during the course of the epidemic by destroying or
inactivating the sources of inoculum (roguing).
 Protection: Reduce the rate of infection by means of a toxicant or some other barrier to infection.
 Resistance: Plant cultivars that can reduce the rate of inoculum production, the rate of infection, or the rate of
pathogen development.
 Therapy: Cure the plants that are already infected or reduce their production of inoculum .

5. Using Traditional Principles
Tactics for the Reduction of the Duration of the Epidemic
 Avoidance: plant early maturing cultivars or plant at a time that favors rapid maturation of the crop.
 Exclusion: delay the introduction of inoculum from external sources by means of plant quarantine.

6. Uses of Epidemiology in plant disease
management
1. The monocyclic disease (loose smut of wheat and wilts) and polycyclic diseases (rust, powdery mildew, and late blight of potato)
should be given different treatment.
2. The information about source of primary inoculum and amount is vital as it can help us in forecasting disease and proper methods
can be employed for disease management.
3. Information about potential for variability in pathogen population can help in adopting suitable breeding strategies, e.g.
management of late blight of potato or wheat rust, with high chances of new races, should emphasized on development of
horizontal resistance.
4. The economic threshold levels, once established may justify the action to be taken for disease management.
5. The behavior of vector populations can be effectively utilized to control plant diseases. This has been demonstrated in case of
potato viruses and stewart’s corn wilt.
6. Disease forecasting can help in adopting the appropriate measures, which can help in reducing pesticides use without risking crop
health.
7. Fungicides should be used judiciously for plant disease management. Contact fungicides are effective only as prophylactic. The
systemic fungicides can be used for eradicative and curative action.

7. Managing Disease through Health of Planting
Material
Healthy Seed Production:
• Epidemiology impacts disease
management by promoting
the production of seed with
reduced or no pathogen
incidence.
• Healthy seed is crucial for
managing disease in
subsequent plant generations.
• Strategies focus on limiting
initial inoculum (Q) to
prevent disease spread.
Inoculum Thresholds and
Models:
• Inoculum thresholds are
established based on
epidemiological studies and
models.
• These models predict disease
transmission considering
critical factors like weather
and cultural practices. .
Seed Health and Developing
Countries:
• Most epidemiology work in
seed health concentrates on
specialized seed production
systems.
• Limited epidemiological
research exists for seed-
borne diseases produced on
farms, especially in
developing countries.
Virus-Free Planting Material:
• Cassava mosaic virus
disease in Africa is managed
using virus-free planting
material.
• Efforts in theoretical
epidemiology address disease
spread within multi-seasonal
production units of
vegetatively propagated
crops.

8. Managing Disease Based on Knowledge of
Spatial Structure of Disease
Diseases intensity can increase over time due to the spread of pathogen propagules at different geographical
scales. When inoculum is spread over large areas, this process is generally considered as inoculum
dispersal. Local dispersal of inoculums usually results in a disease gradient. Knowledge about these
processes can contribute to better understanding of the epidemics and ultimately to better disease
management, although this is one area where a particularly poor linkage between generation of knowledge
and subsequent field implementation has been documented.
Detection of sources
of inoculum (e.g.,
cull piles) of
Phytophthora
infestans in potato
in the Netherlands
Definition of
isolation distances
for peach trees and
roses to avoid
spread of powdery
mildew
To generate
hypotheses about
the mechanism of
dispersal
To make inferences
about the etiological
agent of a unknown
disease, as for
example in the case
of Citrus Sudden
Death (CSD) where
a biological agent
was proposed based
on the disease
gradient
To assess the
efficacy of disease
control measures, as
in the case of
witches broom of
cacao, where a flat
disease gradient was
indicative of
ineffective disease
control
Gradient studies have also been used for a number of other applications including:

9. Case study:
Ascochyta Blight in Chickpea:
Epidemiological studies on D. rabiei, the causative agent of
Ascochyta blight in chickpeas, led to effective management
strategies. Understanding environmental conditions
conducive to the pathogen's activity enabled prediction of
disease onset. Models were developed based on temperature
and moisture levels to forecast pseudothecia maturation and
ascospore discharge, crucial for initiating timely prophylactic
sprays. By targeting primary infections from airborne
ascospores, season-long disease suppression was achieved,
demonstrating the importance of combatting early infections.
.

10. Case study:
Fire Blight in Pears
Climatic factors influencing fire blight infections were
studied extensively, leading to the development of warning
systems such as MARYBLYT in the northeastern USA and
FBCA in Israel. These systems predict infection events based
on temperature and wetness duration. In Israel, the
implementation of FBCA significantly reduced the risk of fire
blight outbreaks in pear orchards. Growers utilized the
system to time bactericide applications and early pruning,
resulting in a steady increase in pear plantation area without
severe outbreaks recorded

11. References :
• https://www.researchgate.net/publication/356283764_Role_of_epidemiology_
in_plant_disease_management.
• https://link.springer.com/chapter/10.1007/978-1-4020-8992-3_14
• https://link.springer.com/chapter/10.1007/978-1-4020-6061-8_3
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9962675/