Any problem with a plant that impacts yield or effects the ...extension.oregonstate.edu/hoodriver/sites/default/files/cgmga/... · Pathogen or Causal Agent: • A specific living

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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:

General Definitions: Pathogen or Causal Agent:

• A specific living organism that causes a contagious disease

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Host:

• A plant that can be infected by or harbor a parasite/pathogen


Susceptible (susceptibility):

A plant (host) that can be infected by a pathogen


Predisposition:

• 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, not enough air movement, or heavy soil.


Resistant:

The ability of the plant/host to reduce or suppress damage of the pathogen.

General Definitions: Symptoms:

Any visual reaction of a plant to a disease

General Definitions: Inoculum or spores:

Portions of the pathogen capable of being moved and causing a new infection.

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Symptom:

•Any visible reaction of a plant to a disease

Abnormal Coloration of the Plant Tissue

• 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 of Plant Tissue

Death

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Death (Necrosis) Rotting Tissue

Canker Necrotic Leaf Spots

Leaf and/or Fruit Drop

Leaf Drop

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5. Abnormal Growth (Increase, appearance) of the Host

Crown Gall on Almond

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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7. Replacement of Plant Tissue with the Pathogen

Loose Smut in Wheat

Ergot in Grass Common Corn Smut

Symptom:

Any visible reaction of a plant to a disease

Any visible part of the pathogen

Sign: Sign

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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?

• Cankers

• Leaf Spots

• Leaf Drops

• Abnormal growth (galls, distortions, abnormal fruit/tuber shape)

• Stunting

• Tissue replacement

Questions?

Plant Disease Triangle

Pathogen

Environment Susceptible

Host


D

I

S

E

A

S

E

Susceptible

Host Environment

Pathogen

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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

What organisms cause infectious diseases?

1. Bacteria

2. Parasitic Seed Plants

3. Fungi

4. Viruses

5. Nematodes

6. Phytoplasma

1. Bacteria

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: • Leaf spots

• Rots

• Cankers

• Blights

• Vascular wilts

Bacterial Diseases

Watermelon

Fruit Blotch

Bacterial Canker--Cherry

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Bacteria in Potato

Black

Leg

Bacterial Blight in Peas

Bacterial Leaf Spot Bacterial Soft Rot

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Bacterial Soft Rot Bacterial Streaming

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Bacterial Streaming

2. Flowering Seed Plants

2. Flowering Seed Plants • 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

Dodder on Potato

Dwarf Mistletoe on Conifer

Witches

Broom

Dwarf Mistletoe on Conifer

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True Mistletoe

3. Fungi

• Bodies made up of thread-like structures (hyphae) • Chains of cells linked together

• Reproduce by spores (asexual and sexual)

• Most plant pathogens do not form mushrooms ……but some do.

3. Fungi • Diseases caused by Fungi: • Root rot

• Foliar spots and blights

• Other rots

• Cankers

• Vascular wilts

• Replacing plant tissue

3. Fungi

Powdery Mildew 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

Silver

Scurf

Black

Dot

Fungus Killing Seedling

Armillaria mellea

• Very small, smaller than bacteria

• Needs a living host to survive and reproduce

• Needs a way to get around

Vector

4. Virus Virus

Rose Mosaic Rose Mosaic

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ZYMV in Squash Pepper Mild Mottle Virus in Pepper

Beet Curley Top Virus

Squash Tomatoes

Beet Curley Top Virus

Tomato

5. Nematode

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• 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: • Root Knot

• Root Lesion

• Cyst

• Stem

• Others

Nematode Nematode

Stylet

Nematode Damage in Potato Nematode Damage in Onions

Nematode Damage in Carrots Nematode Damage in Carrots

Eggs

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6. Phytoplasma (Mycoplasma)

Specialized Bacteria

Live in phloem

Obligate parasites

Need two things:

1. Living Host

2. Vector

Phytoplasma in Potato



•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


Nitrogen

deficiency

caused by

high pH


Nitrogen

Deficiency


Calcium

Deficiency

“Bitter Pit”

8. Pesticides (Herbicides)

Stinger

Sencor

Herbicide Injury on Onion

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9. Air Pollution Toxicity

Ozone Sulfur Dioxide

10. Other….Naturally Occurring Toxic Chemicals

High salt

accumulation

Insect Injury on Lilac Leaf Miner on Beet

Insect Injury Mite Injury on Grape

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Psyllid Injury on Hackberry Aphids on Poplar



2. Non Infectious Diseases:

•Cannot be transmitted (moved) from a diseased plant to a healthy plant.

•Not caused by something living

Disease Management


D

I

S

E

A

S

E

Susceptible

Host Environment

Pathogen

Integrated Disease Management

Reproduced from Kaur, 2016.

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Management of plant Disease

Host Resistance Start with good genetics

Exclusion Clean seed source (certified pathogen-free preferably)

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)

1. Breeding For Resistance

Varieties/Cultivars

Susceptible Resistant

2. Inoculum (spore) Reduction

A. Removal of Infected Plant Nearby

B. Removal of Alternate Hosts, If Possible

Hollyhock Rust Mallow Rust

C. Pruning of Host to Remove Infected Areas

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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


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G. Disease Free Seed and Propagating Material

Silver Scurf

Fusarium and

Blue Mold

H. Steam Treatment of Soil I. Solarization

3. Chemical Control The Use of Fungicides

Two Kinds:

A. Protectant

Go where applied…

B. Systemic

Go everywhere, even where they are not applied

Fungicides Do One of Two Things:

A. Delay or stop fungus growth (fungistatic)

B. Kills the fungus (Fungicidal)

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For Chemical Control to be Effective, the Following Areas Need To Be Addressed

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

4. Biological Control

Kinds

A. Parasites

B. Competitors

Ask questions………LOTS of questions. • Gathering information is almost more important than the actual

diseased plant sample

Things to consider: • 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:

What can they tell you?

Random Uniform 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 http://oregonstate.edu/dept/hermiston/plant-pathology-plant-lab-testing

Plant Pathology Test

1. What are the two remaining components to the plant disease triangle?

1. Host

2. ___________

3. ___________

1. What are the two remaining components to the plant disease triangle?

1. Host

2. Pathogen

3. Environment

2. If one of the three components is missing or unfavorable, will a plant disease problem occur?

Yes_______

No ________

2. If one of the three components is mission or unfavorable, will a plant disease problem occur?

Yes_______

No XXXX

mailto:[email protected]

mailto:[email protected]

http://oregonstate.edu/dept/hermiston/plant-pathology-plant-lab-testing









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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

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________

4. Which of the following is not a symptom caused by a plant disease?

Wilting_________

Stunting________

Virus XXX

Chlorosis________

Yellowing_______

Mortality________

5. Name two additional general groups of plant pathogens?

Nematodes

__________

__________

5. Name two additional general groups of plant pathogens?

Nematodes

Bacteria

Fungi

Virus

Nematode

Phytoplasma

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6. Name three general ways to control a plant disease?

Pesticide

Rouging

Change Environment

7. What is the first thing one should know prior to beginning any kind of plant disease control measure?

Know the disease!

8. Name three sanitation methods for the control of a plant disease?

1. Rouging

2. Solarization

3. Steam treatment of soil

4. Cleaning equipment

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.

10. Name a common plant disease?

Powdery mildew on rose

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?

Allows the spores to germinate and infect.

13. Name a symptom that is caused by this disease from question 10? Carefull!!

Leaf spots and or discoloration

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?

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.

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?

Spores of the pathogen could be on the pruning tools and could be spread.

19. What is a plant disease?

Any problem with a plant that causes (results) in a reduction in yield and or appearance

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

Any problem with a plant that impacts yield or effects the ...extension.oregonstate.edu/hoodriver/sites/default/files/cgmga/... · Pathogen or Causal Agent: • A specific living

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