1. Plant Diseases

2. Objective 8.02
Discuss diseases and viruses.

3. Diseases
A disease is a plant disorder caused by an infectious pathogen or agent

4. Diseases There are 3 conditions necessary for diseases in plants
host plant
disease causing organism or pathogen must be present
favorable environment for disease organism to develop

5. Pathogens There are four groups of pathogens bacteria fungi viruses
parasitic plants (attach to plants)
mistletoe
dodder
lichens

6. Bacteria Single celled microorganisms
Examples of common bacteria diseases:
Leaf spot
Rings of different shades of brown, green or yellow spots on leaves.
Blight
cause plant to quickly turn brown or black as if they had been burned

7. Blight

8. Leaf Spots

9. Fungi Cannot make their own food Examples of common fungi diseases:
They develop hyphae, structures that grow and absorb nutrients from the host plant
Many fungi are spread by spores.
Examples of common fungi diseases:
Damping off causes young plants and seedling to rot off at the soil level.
Rust cause small spots on the leaves that resemble yellow, orange, brown or red rust mainly on the underside of leaves.
Powdery mildew grows on the upper and lower leaf surface as white or gray powdery substance. It is a common disease of houseplants
Galls are round swellings or growths usually on tree branches or leaves.

10. Damping off
A fungal disease that causes young plants and seedlings to rot off at soil level

11. Damping Off

12. Rust
Causes small spots on leaves that resemble yellow, orange, brown or red rust mainly on the underneath side of leaves

13. Rust

14. Mildew
Grows on leaf surfaces--both upper and lower--as white, gray or purple spots

15. Gall
Swellings or growths on plants

16. Examples Examples caused by bacteria or fungi Powdery mildew Blights
Canker
Rots
Wilts and smuts
Galls
Leaf spot
Mildew

17. Viruses Viruses are pathogens with an extremely narrow host range
Examples of common viruses:
Tobacco mosaic virus which attacks tomatoes, peppers, poinsettias and tobacco.
Can be transfer from human hands of a smoker
Be sure to wash your hands before working with plants to control the spread of this virus
Cause leave to have irregular mottled areas with patterns ranging from dark to light green and yellow to white

18. Mosaic
Caused by viruses that make the leaves have irregular mottled areas with patterns ranging from dark green to light green to yellow to white

19. Mosaic

20. Others Diseases

21. Canker
Causes open wounds on woody plants

22. Canker

23. Rots
Cause plant to decay and die

24. Smut
A black, powdery disease that causes blisters that burst open releasing black spores

25. Smut

26. Wilt
A disease that blocks the uptake of water in plant stems causing plants to wilt

27. Wilt