3/15/2016
Pesky Plant Disease: Disease
Identification and Problem
Solving
Kenneth Frost, Ph.D.
Robert Cating, Ph.D.
• Increase our knowledge of plant
diseases
• Integrative science-botany, mycology,
bacteriology, virology, molecular
biology, genomics
• Plant Disease Diagnostics
Any problem with a plant
that impacts yield or effects
the appearance of a plant
General Definitions:
Pathogen or Causal Agent:
General Definitions:
• A specific living organism that causes a
contagious disease
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General Definitions:
Host:
• A plant that can be infected by or harbor a
parasite/pathogen
General Definitions:
Susceptible (susceptibility):
A plant (host) that can be infected by a
pathogen
General Definitions:
General Definitions:
Predisposition:
Resistant:
• Factors that increase the susceptibility of the plant
to infection.
The ability of the plant/host to reduce or suppress
damage of the pathogen.
• Factors like: too much water, not enough water, too
much fertilizer, too little fertilizer, growing the plant
in a shady area, not enough air movement, or heavy
soil.
General Definitions:
General Definitions:
Symptoms:
Inoculum or spores:
Any visual reaction of a plant to a disease
Portions of the pathogen capable of being moved and causing a
new infection.
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Abnormal Coloration of the
Plant Tissue
Symptom:
•Any visible reaction of a plant to
a disease
•
•
•
•
Yellowing (Chlorosis)
Vein Clearing
Interveinal (between veins) yellowing
Mosaic (green and yellow mixed)
Yellowing (Chlorosis)
Vein Clearing
Interveinal Yellow or Necrosis
Mosaic (Green, Yellow, Necrotic Mix)
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Mosaic (Green, Yellow, Necrotic Mix)
Wilt
One of the Most Common
Symptoms
Wilting
Wilting
Death
Death of Plant Tissue
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Death (Necrosis)
Rotting Tissue
Canker
Necrotic Leaf Spots
Leaf Drop
Leaf and/or Fruit Drop
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Crown Gall on Almond
5. Abnormal Growth (Increase,
appearance) of the Host
Western Gall Rust on Pine
Crown Gall on Dahlia
Leaf Distortion
Leaf Distortion
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Abnormal Fruit Shape
6. Stunting of Host
Common Symptom
Stunting in Onions
Stunting in Sweet Corn
Stunting in Peas
Stunting in Potatoes
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Loose Smut in Wheat
7. Replacement of Plant
Tissue with the Pathogen
Ergot in Grass
Common Corn Smut
Symptom:
Any visible reaction of a plant to a
disease
Sign:
Sign
Any visible part of the pathogen
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• Symptoms vs. signs
• Inoculum
What are some commonly encountered
symptoms?
• Yellowing
• Mosaic
• Interveinal necrosis
• Wilting
• Death
What are some commonly encountered
symptoms?
Questions?
• Cankers
• Leaf Spots
• Leaf Drops
• Abnormal growth (galls, distortions, abnormal
fruit/tuber shape)
• Stunting
• Tissue replacement
Plant Disease Triangle
Plant Disease Triangle
Pathogen
Pathogen
Environment
Susceptible
Host
Environment
D
I
S
E
A
S
E
Susceptible
Host
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What organisms cause
infectious diseases?
1. Infectious Diseases:
• Caused by a living organism that is
capable of moving to and/or infecting
another plant
• Biotic
1. Bacteria
2. Parasitic Seed Plants
3. Fungi
4. Viruses
5. Nematodes
6. Phytoplasma
2. Non-Infectious Diseases:
• Abiotic
1. Bacteria
•
•
•
•
Single celled organisms
Some are free living, others need a living host
Reproduce by duplicating cells
Some form spores that are resistant to stressors (temp.,
moisture, etc.)
• Diseases caused by bacteria:
1. Bacteria
•
•
•
•
•
Leaf spots
Rots
Cankers
Blights
Vascular wilts
Bacterial Canker--Cherry
Bacterial Diseases
Watermelon
Fruit Blotch
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Bacteria in Potato
Bacterial Blight in Peas
Black
Leg
Bacterial Leaf Spot
Bacterial Soft Rot
Bacterial Soft Rot
Bacterial Streaming
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Bacterial Streaming
2. Flowering Seed Plants
2. Flowering Seed Plants
Dodder on Potato
• Plants that parasitize other plants
• Some have leaves, other do not
WHY?
•
•
•
•
Parasitic plants with no leaves need…….
Water, nutrients, AND carbohydrates
Parasitic plants with leaves need……
Only water and nutrients, make their own sugars
Dwarf Mistletoe on Conifer
Dwarf Mistletoe on Conifer
Witches
Broom
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True Mistletoe
3. Fungi
3. Fungi
• Bodies made up of threadlike structures (hyphae)
• Chains of cells linked together
• Reproduce by spores
(asexual and sexual)
• Most plant pathogens do
not form mushrooms ……but
some do.
Powdery Mildew
3. Fungi
• Diseases caused by Fungi:
•
•
•
•
•
•
Root rot
Foliar spots and blights
Other rots
Cankers
Vascular wilts
Replacing plant tissue
Powder Mildew
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Powdery Mildew
Rust Life Cycle
Rust Life Cycle
Stripe Rust
Stripe Rust --- Close-up Photo
Rust on Poplar
• Heteroecious, meaning it
requires two hosts to
complete its life cycle
• Alternate host-Douglas
Fir
• Control options?
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Rust on Hollyhock
Snow Mold
Snow Mold Closeup
Snow Mold—Fungus Spores
Pseudocercospora Leaf Spot
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Pseudocercospora Leaf Spot
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Silver Scurf & Black Dot
Fungus Killing Seedling
Black
Dot
Silver
Scurf
Armillaria mellea
4. Virus
Virus
• Very small, smaller than
bacteria
• Needs a living host to survive
and reproduce
• Needs a way to get around
Vector
Rose Mosaic
Rose Mosaic
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ZYMV in Squash
Pepper Mild Mottle Virus
in Pepper
Beet Curley Top Virus
Beet Curley Top Virus
Tomato
Tomatoes
Squash
5. Nematode
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Nematode
• Size: 0.25 to 3 mm long
• Live inside and outside
plants
• Most attack roots but some
can attack above ground
plant parts
• General Nematode Groups:
•
•
•
•
•
Nematode
Stylet
Root Knot
Root Lesion
Cyst
Stem
Others
Nematode Damage in Potato
Nematode Damage in Carrots
Nematode Damage in Onions
Nematode Damage in Carrots
Eggs
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6. Phytoplasma (Mycoplasma)
Phytoplasma in Potato
Specialized Bacteria
Live in phloem
Obligate parasites
Need two things:
1. Living Host
2. Vector
1. Infectious Diseases:
• Caused by a living organism that is
capable of moving to and/or infecting
another plant
• Biotic
2. Non-Infectious Diseases:
• Abiotic
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Oxygen
Lenticels
5. Hail
Sweet
Corn
5. Wind
6. Mineral Excesses
Salt Injury
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7. Mineral Deficiencies
Boron
Deficiency
7. Mineral Deficiencies
Nitrogen
Deficiency
8. Pesticides (Herbicides)
7. Mineral Deficiencies
Nitrogen
deficiency
caused by
high pH
7. Mineral Deficiencies
Calcium
Deficiency
“Bitter Pit”
Herbicide Injury on Onion
Sencor
Stinger
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9. Air Pollution Toxicity
10. Other….Naturally
Occurring Toxic Chemicals
High salt
accumulation
Sulfur Dioxide
Ozone
Insect Injury on Lilac
Leaf Miner on Beet
Insect Injury
Mite Injury on Grape
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Psyllid Injury on Hackberry
1. Infectious Diseases:
• Caused by a living organism that is
capable of moving to and/or infecting
another plant
2. Non Infectious Diseases:
• Cannot be transmitted (moved) from a
diseased plant to a healthy plant.
• Not caused by something living
Plant Disease Triangle
Aphids on Poplar
Disease Management
Integrated Disease Management
Pathogen
Environment
D
I
S
E
A
S
E
Susceptible
Host
Reproduced from Kaur, 2016.
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Management of plant Disease
Host Resistance
Varieties/Cultivars
 Start with good genetics
Exclusion

1. Breeding For Resistance
Clean seed source (certified pathogen-free preferably)
Susceptible
Resistant
Protection – Establish barrier between host and
pathogen (i.e. physical or chemical)
 Host manipulation – avoidance/isolation in space and time (i.e.
separate crop from sources)
 Tillage, drainage, soil pH, depth of seeding, etc.
 Blocking infection (i.e., pesticides, biological control)
Eradication – eliminate pathogen after introduction
 Reducing sources (i.e., identify inoculum, control them)
A. Removal of Infected Plant
Nearby
2. Inoculum (spore)
Reduction
B. Removal of Alternate Hosts,
If Possible
Hollyhock Rust
C. Pruning of Host to Remove
Infected Areas
Mallow Rust
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D. Cleaning of Tools
(Sanitation)
E. Crop Rotation
Because soil will not be depleted of
nutrients and infested by bacteria and
fungi, but rather enriched and
purified, resulting in a diminished
need for fertilizers, bactericides,
fungicides and pesticides.
E. Crop Rotation
E. Crop Rotation
F. Changing Growing
(Cultural) Practices
F. Changing Growing
(Cultural) Practices
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F. Changing Growing
(Cultural) Practices
G. Disease Free Seed and
Propagating Material
Fusarium and
Blue Mold
Silver Scurf
H. Steam Treatment of Soil
I. Solarization
3. Chemical Control
Fungicides Do One of Two
Things:
The Use of Fungicides
Two Kinds:
A. Protectant
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
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Considerations:
A. Identification of the Pathogen
B. Proper Timing of Fungicide Use
C. Life Cycle of the Pathogen needs to be considered
D. Temperature
E. Moisture
F. Beneficials
G. Residues of the Fungicide
H. Proper Chemical
For Chemical Control to be
Effective, the Following Areas
Need To Be Addressed
4. Biological Control
Kinds
Ask questions………LOTS of questions.
A. Parasites
B. Competitors
Things to consider:
• Gathering information is almost more important than the actual
diseased plant sample
•
•
•
•
What signs and symptoms do you see
When did the disease appear?
Remember the Disease Triangle
Damage patterns
• Uniform vs. Non-uniform
• Circular patches or irregular patches
• Strips
Why is an accurate diagnosis
important?
Damage or disease patterns:
Random
Uniform
What can they tell you?
Clustered
• Collect as much of the plant as
possible
• Roots, stems, leaves, soil,
etc.
• Dig samples if possible
• Symptoms may be distant
from true problem
• Plants at different stages of
disease, not just the worst
• Look at lots of symptomatic
plants
• Some may have signs, others
won’t
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• Samples should be as fresh
as possible
• Ship overnight or next day
• Avoid shipping over the
weekend
• Store samples in cool dry
conditions
• Wrap roots in damp towel,
put in plastic bag
• Ship in a sturdy box
• Double wrap to prevent loose
soil or moisture from
escaping
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Contact Information
Ken Frost
Email:
[email protected]
Phone:
541-567-8321 (office)
608-556-9637 (cell)
Robert Cating
Email:
[email protected]
Phone:
541-567-8321 (office)
352-871-0163 (cell)
Address:
2121 S 1st ST
Hermiston, OR 97838
Plant Pathology Test
http://oregonstate.edu/dept/hermiston/plant-pathology-plant-lab-testing
1. What are the two remaining components to the
plant disease triangle?
1. What are the two remaining
components to the plant
disease triangle?
1. Host
2. ___________
3. ___________
1. Host
2. Pathogen
3. Environment
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_______
No ________
Yes_______
No XXXX
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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?
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 __________
Chlorosis________
Yellowing_______
Mortality________
Wilting_________
Stunting________
Virus
XXX
Chlorosis________
Yellowing_______
Mortality________
5. Name two additional general groups of plant
pathogens?
5. Name two additional general groups of plant
pathogens?
Nematodes
Nematodes
Bacteria
Fungi
Virus
Nematode
Phytoplasma
__________
__________
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6. Name three general ways to control a plant disease?
7. What is the first thing one
should know prior to
beginning any kind of plant
disease control measure?
Pesticide
Rouging
Change Environment
Know the disease!
8. Name three sanitation methods
for the control of a plant disease?
1.
2.
3.
4.
Rouging
Solarization
Steam treatment of soil
Cleaning equipment
10. Name a common plant disease?
Powdery mildew on rose
9. What is the difference between
a systemic and protectant
fungicide?
The protectant only “protects” where it is applied
The systemic moves in the plant and will possibly protect
new plant growth.
11. Identify an environmental
condition that favors the disease
that you named in question 10?
Overhead watering
Planting in the shade
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12. Why does the environmental
condition mentioned in
question 11 favor the disease?
13. Name a symptom that is
caused by this disease from
question 10? Carefull!!
Leaf spots and or discoloration
Allows the spores to germinate and infect.
Not the white mycelium….that is a sign!
14. What commonly causes plant
leaves to be distorted?
Herbicides
Insects
Viruses
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.
15. What is the first question to
ask when someone has a
problem with a plant?
What kind of plant is it?
17. When applying a fungicide, why
would one use a systemic instead
of a protectant 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.
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18. Why is it important to
disinfect equipment or tools
when pruning diseased wood
caused by some plant diseases?
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 infect
(and therefore can not reproduce) 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?
22. Name the two most common
factors that contribute to plant
problems which are not caused by a
infectious disease:
Too much water
Not enough water
Too much fertilizer
Too little fertilizer
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