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BASIC PLANT PATHOLOGY Dr. Monica Elliott Ft. Lauderdale REC. WHAT IS A HEALTHY PLANT? . You can’t diagnose a plant problem without knowing how the plant looks when healthy!. PLANTS DON’T TALK! .

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Presentation Transcript
slide1

BASIC

PLANT

PATHOLOGY

Dr. Monica ElliottFt. Lauderdale REC

slide2

WHAT IS A

HEALTHY PLANT?

You can’t diagnose a plant problem without knowing how the plant looks when healthy!

slide5

PLANTS DON’T TALK!

Information about a

plant sample must

come from person

managing the plant !

Ask the right questions!

slide6

Abiotic

vs.

Biotic

slide8

Sooty mold is a fungus, but not a pathogen. It is feeding off insect excretions, such as honeydew.

slide9

Abiotic

  • Injuries
  • Disorders
  • Pathogen is not causing problem
  • Biotic
  • Pathogen is the problem
slide10

INJURY

A destructive physical

occurrence to the plant

slide11

INJURY

NOpathogen!

  • Lightning strikes, Tire tracks
  • Car or lawn equipment exhaust
  • Animals - moles, armadillos, urine
slide14

DISORDER

Interaction between the plant &

its environment that is usually

associated with imbalances of

physical or chemical require-

ments for plant growth.

slide15

DISORDERS

NO pathogen!

  • Cold or heat stress
  • Nutritional, usually deficiencies
  • Air pollution
  • Excessive rainfall or drought
  • Pesticide phytotoxicity
slide17

Drought

Oedema

Both too much and too little water can cause disease-like symptoms.

slide23

SPOTS & PATCHES

  • A plant with a spot does not
  • automatically mean it has a
  • disease.
  • A yellow or dead patch in
  • the lawn does not mean there
  • is a disease.
slide30

DISEASE

Interaction between the plant

and a pathogen that disrupts

the normal growth and

appearance of the plant.

slide31

DISEASE

Three Components:

  • Susceptible host
  • Virulent pathogen
  • Conducive environment

Disease Triangle

slide32

Types of Pathogens

  • Fungi
  • Bacteria
  • Phytoplasmas(mlo)
  • Viruses
  • Viroids

large

small

slide33

Most bacteria can be cultured on artificial media.

Phytoplasmas, viruses and viroids cannot be cultured on media.

slide35

PATHOLOGY TERMS

  • MYCELIA: thread-like material
  • that is body of fungus.
  • SPORES: reproductive structures
  • of a fungus or bacterium
slide36

Bacteria – most enter through natural

  • openings or wounds
  • Viruses – transmitted through wounds
  • made mechanically or by vectors
  • Phytoplasmas – transmitted by vectors
  • Fungi – enter through natural
  • openings, wounds; or by mechanical
  • pressure or enzymes they produce
slide38

FUNGUS - FUNGI

  • No chlorophyll, so no self energy
  • PATHOGEN: obtains energy
  • from living things
  • SAPROPHYTE: obtains energy
  • from dead things
  • SAME fungus can be BOTH a
  • pathogen and a saprophyte!
slide39

PATHOLOGY TERMS

  • SYMPTOMS: how plant expresses
  • the fact it has a disease
  • leaf spots, patches, tip die back, etc.
  • SIGNS: actual pathogen parts
  • associated with a diseased plant
  • spores, mycelia, conks, mushrooms
slide43

Plant

Organs

And

Functions

Disease

Symptoms

slide44

Symptoms

  • spot – small, distinct lesion on leaf, fruit . . .
  • blight – spots that have coalesced or merged
  • together; more tissue being affected
  • rot – tissue is breaking down (fruit, roots);
  • usually mushy, but can be dry
  • wilt – plant droops due to water stress; can
  • be systemic (xylem) or due to root rot
slide45

Symptoms

  • gall – masses of undifferentiated growth; usually on stems or woody tissue
  • (branches) but can be on roots
  • - wart, clubroot, witches’-broom
  • canker – sunken lesions; usually on stems or
  • woody tissue
  • patches, decline – terms often used in
  • association with grasses (turf, grain crops)
slide46

Symptoms Caused by Bacteria

  • leaf spots and blights – water soaked,
  • greasy
  • soft rots of fruits
  • wilts (systemic – xylem)
  • gall (overgrowths/cell proliferation)
  • cankers
slide49

Symptom:Wilt

Symptom:Gall

slide50

Symptoms Caused by Viruses

  • dwarfing or stunting to some degree
  • mosaics – light green, yellow or white
  • areas intermingled with green – leaves
  • or fruits
  • ring spots – chlorotic or necrotic rings –
  • leaves, fruits or stems
  • are always systemic infections
slide54

Symptoms Caused by Fungi

  • leaf spots and blights (including rust and
  • powdery mildew)
  • soft or dry rots of fruits, bulbs . . .
  • root rots
  • wilts (systemic – xylem)
  • overgrowths/cell proliferation –
  • clubroot, galls, warts, witches’-broom
  • scabs, cankers, patches and decline
slide60

PATHOLOGY TERMS

  • PATHOGENESIS: the pathogen either
  • does or does not cause a disease
  • yes or no question
  • VIRULENCE: severity level of the
  • disease that a pathogen causes
  • minimal damage vs. dead plant
slide61

Plant Samples

  • Goal is to have plant sample arrive in
  • diagnostic laboratory looking like it did in
  • the field or landscape.
  • Keep roots moist, but do not place any other
  • tissue inside plastic bag.
  • Ask the right questions, fill out form
  • completely. It is critical to have background
  • information about the situation.
slide62

Plant Samples

  • Ask the right questions:
  • What is the plant?
  • Where is plant growing?
  • Is this sample typical?
  • When did symptoms appear?
  • Fertility and pesticide applications?
slide64

Plant Samples

  • Best samples are those that exhibit
  • progression of symptoms – e.g., leaf spot to
  • leaf blight to severely diseased plant.
  • Best to examine entire plant, if possible, as
  • root disease could be cause for leaf symptoms
  • Good pictures are useful, illustrating overall
  • symptoms and close-ups
slide65

Plant Samples

  • Soil samples for disease diagnosis are useless.
  • Do not be afraid to tell a client that the sample is inadequate. We are not miracle workers!
  • It is better to make no diagnosis than to make the wrong diagnosis, especially if it is a valuable specimen or pesticides are required.
slide67

Three “Little” Steps

1. Identify the disease.

2. Identify the conditions

causing disease diagnosed.

3. Identify the management techniques

that will alter the disease-conducive

conditions causing disease diagnosed.

SureLook

Holmes

slide68

DISEASE

Three Components:

  • Susceptible host
  • Virulent pathogen
  • Conducive environment

Disease Triangle

slide69

Plant Disease Control

Integrated Approach

  • Pathogen exclusion or sanitation
  • Plant resistance (genetic)
  • Cultural methods
  • Chemical methods
slide70

Plant Disease Control

  • Pathogen exclusion
  • - via regulation
  • - via ‘just don’t bring it home no
  • matter how cute it looks’ if it has a
  • spot, wilt, etc.
slide72

Plant Disease Control

  • Plant resistance (genetic)
  • Immunity is the rule in the plant
  • kingdom
  • Where immunity does not exist, plant
  • breeders have developed cultivars
  • with resistance to specific pathogens.
slide73

Plant Disease Control

  • Plant resistance (genetic)
slide74

Plant Disease Control

  • Plant resistance (genetic)
  • - breeding for resistance to pathogen
  • - plant adaptation to site (right plant
  • for the right site concept)
  • - monoculture vs. mixed culture
slide75

Plant Disease Control

  • Cultural methods
  • - crop rotation
  • - host eradication (alternate hosts)
  • - improved plant environment,
  • especially water management
slide76

Plant Disease Control

  • Cultural methods
  • - sanitation of
  • tools, pots, shoes,
  • equipment, etc.
slide77

Plant Disease Control

  • Chemical methods
  • - seed treatments
  • - soil treatments/root drenches
  • - foliar sprays
  • - trunk injections
slide78

Plant Disease Control

  • Chemical methods
  • critical to understand that chemicals do
  • not necessarily eliminate symptoms
  • observed
  • most chemicals prevent disease from
  • ever occurring or keep it from spreading
slide79

Plant Disease Control

  • Chemical methods
  • ex: leaf spots don’t disappear, but old leaves with spots die and new growth is healthy and spot free
  • ex: rotted roots eventually die, but new roots are healthy and take their place to supply water and nutrients
slide80

Plant Disease Control

  • Chemical methods
  • “The label is the law.”
  • Pesticide labels must be followed, even by homeowners – safety to applicator and environment.
  • The site for application must be on the label – turf vs. ornamentals.
slide81

Plant Disease Control

Some diseases do not have ANY control methods.

slide82

Proactive vs. Reactive

The single best method

for controlling diseases

is to prevent them!