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