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General kinds of plant diseases:
What is a plant disease?
1. Non infectious:
– Can not be transmitted (or moved) from a
disease pplant to a healthyy pplant.
Any problem with a plant that
causes a reduction in yield or
appearance.
– Not caused by something living
1. Low Temperature
Kinds of non-infectious diseases:
2. High Temperature
3. Unfavorable Oxygen Levels
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4. Unfavorable Water Levels
5. Lightning
5. Wind
5. Hail
Sweet
Corn
6. Mineral Excesses
7. Mineral Deficiencies
Boron
Deficiency
Salt Injury
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7. Mineral Deficiencies
7. Mineral Deficiencies
Nitrogen
deficiency
caused by
high pH
Nitrogen
g
Deficiency
8. Pesticides (Herbicides)
7. Mineral Deficiencies
Calcium
Deficiency
“Bitter Pit”
Stinger
Sencor
10. Other…Soil Compaction
9. Air Pollution Toxicity
Sulfur Dioxide
Ozone
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10. Other….Naturally Occurring
Toxic Chemicals
General kinds of plant diseases:
1. Non infectious:
High salt
accumulation
l ti
– Can not be transmitted (or moved) from a
disease pplant to a healthyy pplant.
– Not caused by something living
2. Infectious:
– Caused by a living organism that is capable of
moving to and/or infecting another plant.
Plant Disease Triangle
Plant Disease Triangle
Pathogen
Pathogen
D
I
S
E
A
S
E
Environment
Environment
Susceptible
Host
Susceptible
Host
Kinds (what causes) of Infectious
diseases:
1. Bacteria
2. Parasitic Seed Plants
3. Fungi
4. Viruses
5. Nematodes
6. Phytoplasma
1. Bacteria
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Bacterial Diseases
Bacterial Canker--Cherry
Watermelon
Fruit Blotch
Bacteria in Potato
Bacterial Blight in Peas
Bacterial Streaming
2. Flowering Seed Plants
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Dodder on Potato
Dwarf Mistletoe on Conifer
Dodder on Potato
Dwarf Mistletoe on Conifer
True Mistletoe
3. Fungi
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Powdery Mildew
Powder Mildew
The “thumb test
Powdery Mildew
Stripe Rust
Stripe Rust --- Close-up Photo
Rust on Poplar
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Rust on Hollyhock
Snow Mold
Snow Mold Closeup
Snow Mold—Fungus Spores
Silver Scurf & Black Dot
Fungus Killing Seedling
Silver Scurf
Black Dot
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4. Virus
Virus
Needs a vector
Rose Mosaic
Rose Mosaic
ZYMV in Squash
Pepper Mild Mottle Virus in
Pepper
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Beet Curley Top Virus
Beet Curley Top Virus
Tomato
Squash
Tomatoes
Nematode
-Size: 0.25 to 3 mm long
-Live inside and outside plants
-Most
Most attack roots but some can
attack above ground plant parts
5. Nematode
Nematode
Nematode Damage in Potato
Stylet
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Nematode Damage in Onions
Nematode Damage in Carrots
Nematode Damage in Carrots
6. Phytoplasma (Mycoplasma)
•
•
•
•
Eggs
Specialized Bacteria
Live in phloem
Obligate
g parasites
p
Need two things:
1. Living Host
2. Vector
Phytoplasma in Potato
General Definitions:
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General Definitions:
• Pathogen or Causal Agent:
A specific living organism that causes a
g
disease
contagious
General Definitions:
• Symptoms:
Any visual reaction of a plant to a disease
Living organism: Bacteria, fungus, nemotode,
virus, plant etc
General Definitions:
• Inoculum or spores:
General Definitions:
• Life Cycle
Portions of the pathogen capable of being moved
and causingg a new infection.
The series of changes undergone by the
organism….the
g
pathogen
p
g in this case.
Typical Fungus Life Cycle
General Definitions:
• Susceptible (susceptibility):
A plant that can be infected by a pathogen
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General Definitions:
• Resistant:
General Definitions:
• Predisposition:
The ability of the plant to reduce or suppress
g of the pathogen.
p
g
damage
Factors that increase the susceptibility of the plant
to infection.
Factors like: too much water, not enough water,
too much fertilizer, too little fertilizer, growing
the plant in a shady area, or heavy soil.
1. Abnormal Coloration of the
Plant Tissue
Symptom:
Any visible reaction of a plant to
a disease
Sign:
Any visible part of the pathogen
A. Yellowing (Chlorosis)
•
•
•
•
A. Yellowing (Chlorosis)
B. Vein Clearing
C. Interveinal (between veins) yellowing
D. Mosaic (green and yellow mixed)
B. Vein Clearing
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C. Interveinal Yellow or Necrosis
D. Mosaic (Green, Yellow,
Necrotic Mix)
Wilting
2. Wilt
One of the Most Common Symptoms
Caused by root rot or lack of water?
Wilting
3. Death of Plant Tissue
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A. Death (Necrosis)
B. Rot
C. Canker
4. Leaf and/or Fruit Drop
Leaf Drop
5. Abnormal Growth (Increase,
appearance)
pp
) of the Host
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Crown Gall on Almond
Western Gall Rust on Pine
Crown Gall on Dahlia
ZYMV on Cantaloupe
ZYMV on Yellow Crook-Neck
Squash
6. Stunting of Host
Common Symptom
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Stunting in Onions
Stunting in Sweet Corn
Stunting in Peas
Stunting in Potatoes
Loose Smut in Wheat
7. Replacement of Plant Tissue
with the Pathogen
g
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Ergot in Grass
Common Corn Smut
Symptom:
Any visible reaction of a plant to
a disease
Sign
Si
Sign:
Any visible part of the pathogen
Herbicide Injury on Onion
Not Disease Problems
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Insect Injury on Lilac
Leaf Miner on Beet
Insect Injury
Mite Injury on Grape
What Causes This Symptom?
Psyllid Injury on Hackberry
Aphids on Poplar
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1. Breeding For Resistance
Disease Control
A. Removal of Infected Plant
Nearby
2. Inoculum (spore) Reduction
B. Removal of Alternate Hosts
Hollyhock Rust
C. Pruning of Host to Remove
Infected Areas
Mallow Rust
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D. Cleaning of Tools (Sanitation)
E. Crop Rotation
Thi Year’s
This
Y ’
Watermelon Field
Last Year’s
Watermelon Field
F. Changing Growing (Cultural)
Practices
G. Disease Free Seed and
Propagating Material
Silver Scurf
H. Steam Treatment of Soil
Watermelon 2
Years in a Row
Fusarium and
Blue Mold
I. Solarization
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3. Chemical Control
• The Use of Fungicides
– Two Kinds:
A Protectant
A.
Fungicides Do One of Two
Things:
A. Delay or stop fungus growth (fungistatic)
B. Kills the fungus (Fungicidal)
Go where applied…
B. Systemic
Go everywhere, even where they are not
applied
For Chemical Control to be
Effective, the Following Areas
Need To Be Addressed
Considerations Cont.
G. Residues of the Fungicide
H. Proper Chemical
Considerations:
A. Identification of the Pathogen
B. Proper Timing of Fungicide Use
C Life Cycle of the Pathogen needs to be
C.
considered
D. Temperature
E. Moisture
F. Beneficials
4. Biological Control
• Kinds
A. Parasites
B C
B.
Competitors
tit
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Diagnosing Diseases
Practicing Diagnosing
• Ask questions………LOTS of questions.
• Remember the Disease Triangle
• Things to consider:
– When and where the disease appeared
– Damage patterns: Uniform vs. Non-uniform
– What signs and symptoms do you see
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111111111
111111111
111111111
111111111
111111111
1
Healthy
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Plant Pathology Test
1. What are the two remaining
components to the plant disease
triangle?
1. Host
1
2. ___________
3. ___________
1. What are the two remaining
components to the plant
disease triangle?
1. Host
1
2. Pathogen
3. Environment
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2. If one of the three components
is missing or unfavorable, will
a plant disease problem occur?
2. If one of the three components
is mission or unfavorable, will a
plant disease problem occur?
• Yes
Yes_______
• No ________
• Yes_______
Yes
• No XXXX
3. Which of the following is an
example of a noninfectious
disease?
________Low Temperature
________Bacteria
________Mineral Excess
________Pesticides
________Fungi
________Air Pollution
4. Which of the following is not a
symptom caused by a plant
disease?
Wilting_________
Stunting________
Virus __________
Chlorosis________
Yellowing_______
Mortality________
3. Which of the following is an
example of a noninfectious
disease?
XXX Low Temperature
_____Bacteria
XXX Mineral Excess
XXX Pesticides
_____Fungi
XXX Air Pollution
4. Which of the following is not a
symptom caused by a plant
disease?
Wilting_________
Stunting________
Virus
XXX
Chlorosis________
Yellowing_______
Mortality________
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5. Name two additional general
groups of plant pathogens?
• Nematodes
__________
__________
6. Name three general ways to
control a plant disease?
• Pesticide
• Rouging
• Change Environment
8. Name three sanitation methods
for the control of a plant disease?
1.
2
2.
3.
4.
5.
6.
Rouging
Pruning
Solarization
Steam treatment of soil
Cleaning equipment
Removal of alternate hosts
5. Name two additional general
groups of plant pathogens?
•
•
•
•
•
•
Nematodes
Bacteria
Fungi
Virus
Nematode
Phytoplasma
7. What is the first thing one
should know prior to
beginning any kind of plant
disease control measure?
Know the disease!
9. What is the difference between
a systemic and protectant
fungicide?
• The p
protectant onlyy “protects”
p
where it is
applied
• The systemic moves in the plant and will
possibly protect new plant growth.
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10. Name a common plant
disease?
• Powdery mildew on rose
12. Why does the environmental
condition mentioned in
question 11 favor the disease?
11. Identify an environmental
condition that favors the disease
that you named in question 10?
• O
Overhead
h d watering
t i
• Planting in the shade
13. Name a symptom that is
caused by this disease from
question 11? Carefull!!
• Leaf spots and or discoloration
• Allows
All
the
th spores to
t germinate
i t andd infect.
i f t
• Not the white mycelium….that is a sign!
14. What commonly causes plant
leaves to be distorted?
• Herbicides
• Insects
• Viruses
15. What is the first question to
ask when someone has a
problem with a plant?
• What kind of plant is it!!!!!
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16. Why is it sometimes important to
remove plant residue from the
previous crop before replanting?
• Spores from the previous crop may be
found in the residue.
18. Why could it be important to
disinfect equipment or tools
when pruning disease wood
caused by
y some pplant diseases?
17. When applying fungicide, why
would one use a systemic instead
of a protectant material if both
were available for controlling the
same disease problem?
• Because the application doesn’t have to be
100 % coverage and new foliage is
protected.
19. What is a plant disease?
• Any problem with a plant that causes
(results) in a reduction in yield and or
appearance
• Spores of the pathogen could be on the
pruning tools and could be spread.
20. Why is crop rotation
important for controlling some
kinds of plant disease problems?
• Reduce soil borne pathogens in the soil that
do not feed (and therefore can not
reproduce) on the rotational crops.
21. Name a general group of plant
pathogens that can never be seen
without the aid of a microscope?
•
•
•
•
Viruses
Bacteria
Phytoplasma
Nematodes?
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22. Name the two most common
factors that contribute to plant
problems that are not caused by a
infectious disease?
•
•
•
•
Too much water
Not enough water
Too much fertilizer
Too little fertilizer
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