Transcript What is a healthy plant?

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!
Information about a
plant sample must
come from person
managing the plant !
Ask the right questions!
Abiotic
vs.
Biotic
But, first rule
out those pesky
insects
Sooty mold is a fungus, but not a
pathogen. It is feeding off insect
excretions, such as honeydew.
Abiotic
• Injuries
• Disorders
• Pathogen is not causing problem
Biotic
• Pathogen is the problem
INJURY
A destructive physical
occurrence to the plant
INJURY
NO pathogen!
• Lightning strikes, Tire tracks
• Car or lawn equipment exhaust
• Animals - moles, armadillos, urine
DISORDER
Interaction between the plant &
its environment that is usually
associated with imbalances of
physical or chemical requirements for plant growth.
DISORDERS
NO pathogen!
• Cold or heat stress
• Nutritional, usually deficiencies
• Air pollution
• Excessive rainfall or drought
• Pesticide phytotoxicity
Cold Damage
Oedema
Drought
Both too much and too little water can
cause disease-like symptoms.
Sunburned palm leaf
Manganese
deficiency
Manganese
deficiency
Potassium
deficiency
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.
Chinchbug damage
Typical
injury from
growth
regulator
type
herbicide
DISEASE
Interaction between the plant
and a pathogen that disrupts
the normal growth and
appearance of the plant.
DISEASE
Three Components:
• Susceptible host
• Virulent pathogen
• Conducive environment
Disease Triangle
Types of Pathogens
large
small
• Fungi
• Bacteria
• Phytoplasmas (mlo)
• Viruses
• Viroids
Most bacteria can
be cultured on
artificial media.
Phytoplasmas,
viruses and viroids
cannot be cultured
on media.
Most fungi can be cultured on
artificial media, but not all.
PATHOLOGY TERMS
• MYCELIA: thread-like material
that is body of fungus.
• SPORES: reproductive structures
of a fungus or bacterium
• 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
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!
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
Signs of Disease
Signs of Disease
Signs of Disease
Plant
Disease
Organs
Symptoms
And
Functions
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
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)
Symptoms Caused by Bacteria
• leaf spots and blights – water soaked,
greasy
• soft rots of fruits
• wilts (systemic – xylem)
• gall (overgrowths/cell proliferation)
• cankers
Symptom:
Water soaked or greasy leaf spots
Symptom:
Water soaked or
greasy leaf blight
Symptom:
Wilt
Symptom:
Gall
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
Symptom:
Dwarfing
and
Stunting
Symptom:
Mosaic
Symptom:
Ringspot
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
Symptom:
Leaf spots
and blight
Symptom:
Soft or dry rots
Symptom:
Wilt
Symptom:
Patches and
Decline
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
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.
Plant Samples
• Ask the right questions:
1) What is the plant?
2) Where is plant growing?
3) Is this sample typical?
4) When did symptoms appear?
5) Fertility and pesticide applications?
Plant Samples
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
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.
Three “Little” Steps
1. Identify the disease.
2. Identify the conditions
causing disease diagnosed.
SureLook
Holmes
3. Identify the management techniques
that will alter the disease-conducive
conditions causing disease diagnosed.
DISEASE
Three Components:
• Susceptible host
• Virulent pathogen
• Conducive environment
Disease Triangle
Plant Disease Control
Integrated Approach
• Pathogen exclusion or sanitation
• Plant resistance (genetic)
• Cultural methods
• Chemical methods
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.
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.
Plant Disease Control
• Plant resistance (genetic)
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
Plant Disease Control
• Cultural methods
- crop rotation
- host eradication (alternate hosts)
- improved plant environment,
especially water management
Plant Disease Control
• Cultural methods
- sanitation of
tools, pots, shoes,
equipment, etc.
Plant Disease Control
• Chemical methods
- seed treatments
- soil treatments/root drenches
- foliar sprays
- trunk injections
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
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
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.
Plant Disease Control
Some diseases do not
have ANY control
methods.
Proactive vs. Reactive
The single best method
for controlling diseases
is to prevent them!