Vegetable Diseases: Identification & Management
2012 Home Vegetable Gardening Series
1. Diagnostic principles2. 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
THE ART OF DISEASE DIAGNOSIS
The Nature of Disease
Disease Disorder Damage
Irritation Continuous Continuous Transitory
Contagious Yes No No
Causal agent
Biotic AbioticBiotic & Abiotic
Major Causes of Plant Diseases
Fungi the “Water Molds” Nematodes Bacteria
Actinomycetes Phytoplasmas
Viruses Viroids
Abiotic Causes
Insufficient soil moisture
Excess soil moisture
Oxygen deprivation Soil compaction Temperature
extremes
Air pollution Salinity Soil pH Nutrient deficiency Nutrient toxicity
Improper cultural practices
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
Disease Identification
Field Observations
Plant parts affected
Sequence of events in the development of symptoms
Pattern of disease development
Association with: terrain weather plant
development other plants
Ozone damage
Ozone damage
Magnesium deficiency
Lenticel enlargement due to low O2
Blossom end rot or poor pollination?
The Disease Cycle(The Infection Chain)
Monocyclic disease development
Pathogen goes through one (or very few) generations during the growing season (or dispersal is limited)
Amount of disease is related to amount of initial inoculum
Polycyclic disease development
Pathogen goes through many generations during the growing season (and dispersal is not limited)
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 period: the time required for infection to occur under favorable environmental
conditions
Penetration
Inoculation
Infection
Dispersal
Colonization
Reproduction
Incubation period: the time from penetration of the host by the pathogen to the first appearance of
symptoms
Penetration
Inoculation
Infection
Dispersal
Colonization
Reproduction
Latent period: the time from the beginning of the infection process to the first appearance of
secondary inoculum
Penetration
Inoculation
Infection
Dispersal
Colonization
Reproduction
Infectious period: the time during which a pathogen is reproducing and capable of being
dispersed
Penetration
Inoculation
Infection
Dispersal
Colonization
Reproduction