Transcript Major Causes of Plant Diseases

Vegetable Diseases:
Identification & Management
2012 Home Vegetable Gardening
Series
1. Diagnostic principles
2. Practical means of identification
3. Practical means of protection or avoidance
4. Standard and organic remedies for the
most common pests and diseases
5. Resources and references
Irritation
Contagious
Causal agent
Disease
Disorder
Damage
Continuous
Continuous
Transitory
Yes
No
No
Biotic
Abiotic
Biotic & Abiotic




Fungi
the “Water Molds”
Nematodes
Bacteria



Actinomycetes
Phytoplasmas
Viruses

Viroids





Insufficient soil
moisture
Excess soil moisture
Oxygen deprivation
Soil compaction
Temperature extremes






Air pollution
Salinity
Soil pH
Nutrient deficiency
Nutrient toxicity
Improper cultural
practices
Disease Identification

Primary symptoms



the first symptoms to appear
generally occur at or near the infection site
Secondary symptoms


the subsequent symptoms that appear
generally occur some distance away from the
infection site
Disease Identification


Symptoms: visible alterations of the host as a
result of disease
Signs: physical manifestation of the pathogen
itself in or on diseased tissues


Plant parts affected
Sequence of events in
the development of
symptoms

Pattern of disease
development

Association with:
 terrain
 weather
 plant development
 other plants
The Disease Cycle
(The Infection Chain)
Monocyclic disease
development
Polycyclic disease
development
Pathogen goes through one (or
very few) generations during the
growing season (or dispersal is
limited)
Pathogen goes through many
generations during the growing
season (and dispersal is not
limited)
Amount of disease is related to
amount of initial inoculum
Amount of disease is related to
the rate of growth, reproduction
and spread of the pathogen
Infection period:
the time required for infection to occur under favorable
environmental conditions
Incubaton period:
the time from penetration of the host by the pathogen
to the first appearance of symptoms
Latent period:
the time from the beginning of the infection process to
the first appearance of secondary inoculum
Infectious period:
the time during which a pathogen is reproducing and
capable of being dispersed
Infection
Penetration
Inoculation
Colonization
Reproduction
Dispersal
Infection
Penetration
Inoculation
Colonization
Reproduction
Dispersal
Infection
Penetration
Inoculation
Colonization
Reproduction
Dispersal
Infection
Penetration
Inoculation
Colonization
Reproduction
Dispersal