Plant diseases

3/9/2011

1

What is a plant disease?

Any problem with a plant that causes a reduction in yield or

appearance.

General kinds of plant diseases:

1. Non infectious:– Can not be transmitted (or moved) from a

disease plant to a healthy plant.p y p

– Not caused by something living

Kinds of non-infectious diseases:

1. Low Temperature

2. High Temperature 3. Unfavorable Oxygen Levels

3/9/2011

2

4. Unfavorable Water Levels5. Lightning

5. Hail

Sweet Corn

5. Wind

6. Mineral Excesses

Salt Injury

7. Mineral Deficiencies

Boron Deficiency

3/9/2011

3


Nitrogen deficiencydeficiency caused by high pH


Nitrogen gDeficiency


Calcium DeficiencyDeficiency

“Bitter Pit”

8. Pesticides (Herbicides)

Stinger Sencor

9. Air Pollution Toxicity

OzoneSulfur Dioxide

10. Other…Soil Compaction

3/9/2011

4

10. Other….Naturally Occurring Toxic Chemicals

High salt l tiaccumulation

General kinds of plant diseases:

1. Non infectious:– Can not be transmitted (or moved) from a

disease plant to a healthy plant.p y p

– 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

Pathogen

EnvironmentSusceptible

Host

Plant Disease Triangle

Pathogen

DISEASE Susceptible

HostEnvironment

Kinds (what causes) of Infectious diseases:

1. Bacteria2. Parasitic Seed Plants3. Fungi4. Viruses5. Nematodes6. Phytoplasma

1. Bacteria

3/9/2011

5

Bacterial Diseases

Watermelon Fruit Blotch

Bacterial Canker--Cherry

Bacteria in PotatoBacterial Blight in Peas

Bacterial Streaming

2. Flowering Seed Plants

3/9/2011

6

Dodder on Potato Dodder on Potato

Dwarf Mistletoe on Conifer Dwarf Mistletoe on Conifer

True Mistletoe

3. Fungi

3/9/2011

7

Powdery Mildew Powder Mildew

The “thumb test

Powdery Mildew Stripe Rust

Stripe Rust --- Close-up Photo Rust on Poplar

3/9/2011

8

Rust on Hollyhock Snow Mold

Snow Mold Closeup Snow Mold—Fungus Spores

Silver Scurf & Black Dot

Silver ScurfBlack Dot

Fungus Killing Seedling

3/9/2011

9

4. Virus

Needs a vector

Virus

Rose Mosaic Rose Mosaic

ZYMV in SquashPepper Mild Mottle Virus in

Pepper

3/9/2011

10

Beet Curley Top Virus

Squash Tomatoes

Beet Curley Top Virus

Tomato

5. Nematode

Nematode

-Size: 0.25 to 3 mm long-Live inside and outside plants-Most attack roots but some canMost attack roots but some can attack above ground plant parts

Nematode

Stylet

Nematode Damage in Potato

3/9/2011

11

Nematode Damage in Onions Nematode Damage in Carrots

Nematode Damage in Carrots

Eggs

6. Phytoplasma (Mycoplasma)

• Specialized Bacteria

• Live in phloem

• Obligate parasitesg p

• Need two things:

1. Living Host

2. Vector

Phytoplasma in Potato

General Definitions:

3/9/2011

12


• Pathogen or Causal Agent:A specific living organism that causes a

contagious diseaseg

Living organism: Bacteria, fungus, nemotode, virus, plant etc


• Symptoms:Any visual reaction of a plant to a disease


• Inoculum or spores:Portions of the pathogen capable of being moved

and causing a new infection.g


• Life CycleThe series of changes undergone by the

organism….the pathogen in this case.g p g

Typical Fungus Life Cycle


• Susceptible (susceptibility):A plant that can be infected by a pathogen

3/9/2011

13


• Resistant:The ability of the plant to reduce or suppress

damage of the pathogen.g p g


• 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, or heavy soil.

Symptom:

Any visible reaction of a plant to a disease

Sign:

Any visible part of the pathogen

1. Abnormal Coloration of the Plant Tissue

• A. Yellowing (Chlorosis)

• B. Vein Clearing

• C. Interveinal (between veins) yellowing

• D. Mosaic (green and yellow mixed)

A. Yellowing (Chlorosis) B. Vein Clearing

3/9/2011

14

C. Interveinal Yellow or NecrosisD. Mosaic (Green, Yellow,

Necrotic Mix)

2. Wilt

One of the Most Common Symptoms

Wilting

Caused by root rot or lack of water?

Wilting

3. Death of Plant Tissue

3/9/2011

15

A. Death (Necrosis) B. Rot

C. Canker

4. Leaf and/or Fruit Drop

Leaf Drop

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

3/9/2011

16

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

3/9/2011

17

Stunting in Onions Stunting in Sweet Corn

Stunting in Peas Stunting in Potatoes

7. Replacement of Plant Tissue with the Pathogeng

Loose Smut in Wheat

3/9/2011

18

Ergot in Grass Common Corn Smut

Symptom:

Any visible reaction of a plant to a disease

Sign:

Any visible part of the pathogen

SiSign

Not Disease Problems

Herbicide Injury on Onion

3/9/2011

19

Insect Injury on Lilac Leaf Miner on Beet

Insect Injury

What Causes This Symptom?

Mite Injury on Grape

Psyllid Injury on Hackberry Aphids on Poplar

3/9/2011

20

Disease Control

1. Breeding For Resistance

2. Inoculum (spore) Reduction

A. Removal of Infected Plant Nearby

B. Removal of Alternate Hosts

Hollyhock Rust Mallow Rust

C. Pruning of Host to RemoveInfected Areas

3/9/2011

21

D. Cleaning of Tools (Sanitation) E. Crop Rotation

Thi Y ’

Watermelon 2 Years in a Row

This Year’s Watermelon Field

Last Year’s Watermelon Field

F. Changing Growing (Cultural) Practices

G. Disease Free Seed and Propagating Material

Silver Scurf Fusarium and Blue Mold

H. Steam Treatment of Soil I. Solarization

3/9/2011

22

3. Chemical Control

• The Use of Fungicides

– Two Kinds:

A ProtectantA. ProtectantGo where applied…

B. SystemicGo 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)

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 beC. Life Cycle of the Pathogen needs to be

considered

D. Temperature

E. Moisture

F. Beneficials

Considerations Cont.

G. Residues of the Fungicide

H. Proper Chemical

4. Biological Control

• KindsA. Parasites

B C titB. Competitors

3/9/2011

23

Practicing Diagnosing

Diagnosing Diseases

• Ask questions………LOTS of questions.

• Remember the Disease Triangle

• Things to consider:• Things to consider:– When and where the disease appeared

– Damage patterns: Uniform vs. Non-uniform

– What signs and symptoms do you see

3/9/2011

24

3/9/2011

25

1111111111111111111111111111111111111111111111111111111

Healthy

3/9/2011

26

Plant Pathology Test

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

triangle?

1 Host1. Host

2. ___________

3. ___________

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

1 Host1. Host

2. Pathogen

3. Environment

3/9/2011

27

2. If one of the three componentsis missing or unfavorable, willa plant disease problem occur?

• YesYes_______

• No ________

2. If one of the three components is mission or unfavorable, will a

plant disease problem occur?

• YesYes_______

• No XXXX

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________

3/9/2011

28

5. Name two additional general groups of plant pathogens?

• Nematodes__________

__________

5. Name two additional general groups of plant pathogens?

• Nematodes

• BacteriaBacteria

• Fungi

• Virus

• Nematode

• Phytoplasma

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

• Pesticide

• Rouging• 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 methodsfor the control of a plant disease?

1. Rouging

2 Pruning2. Pruning

3. Solarization

4. Steam treatment of soil

5. Cleaning equipment

6. Removal of alternate hosts

9. What is the difference betweena systemic and protectant fungicide?

• The protectant only “protects” where it is p y papplied

• The systemic moves in the plant and will possibly protect new plant growth.

3/9/2011

29

10. Name a common plant disease?

• Powdery mildew on rose

11. Identify an environmentalcondition that favors the diseasethat you named in question 10?

O h d t i• Overhead watering

• Planting in the shade

12. Why does the environmentalcondition mentioned in question 11 favor the disease?

All th t i t d i f t• Allows the spores to germinate and infect.

13. Name a symptom that is caused by this disease from question 11? Carefull!!

• Leaf spots and or discoloration

• Not the white mycelium….that is a sign!

14. What commonly causes plantleaves 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!!!!!

3/9/2011

30

16. Why is it sometimes important toremove plant residue from the previous crop before replanting?

• Spores from the previous crop may be found in the residue.

17. When applying fungicide, why would one use a systemic insteadof a protectant material if both were available for controlling thesame disease problem?same disease problem?

• Because the application doesn’t have to be 100 % coverage and new foliage is protected.

18. Why could it be important to disinfect equipment or toolswhen pruning disease wood caused by some plant diseases?y p

• 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(results) in a reduction in yield and or appearance

20. Why is crop rotation important for controlling somekinds 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 plantpathogens that can never be seenwithout the aid of a microscope?

• Viruses

• Bacteria

• Phytoplasma

• Nematodes?

3/9/2011

31

22. Name the two most commonfactors that contribute to plant problems that are not caused by ainfectious disease?

• Too much water

• Not enough water

• Too much fertilizer

• Too little fertilizer

Education

Plant diseases