8 0 Pest Management 8 02 Discuss diseases

8. 0 Pest Management 8. 02 Discuss diseases and viruses

Plant Diseases �Definition: Disease is a plant disorder caused by an infectious pathogen or agent

Three Conditions Necessary for diseases in plants �Host plant The plant the disease attacks �Disease causing organism or pathogen must be present �Favorable environment for disease organism to develop Moist and warm

Disease Triangle

Groups of Pathogens �Bacteria �Fungi �Viruses

Bacteria �Bacteria are single celled microorganisms �Examples of common bacteria diseases: Bacterial leaf spot are rings of different shades of brown, green or yellow spots on leaves Bacterial blight cause plants to quickly turn brown or black as if they had been burned

Leaf Spot

Blight

Fungi �Fungi cannot make their own food They develop hyphae, structures that grow and absorb nutrients from the host plant Many fungi are spread by spores

Fungi �Examples of common fungi diseases: Damping off Rust Powdery Mildew Galls

Damping Off �Causes young plants and seedlings to rot off at the soil level

Rust �Causes small spots on the leaves that resemble yellow, brown, orange 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 A common disease of houseplants

Galls �Round swellings or growths usually on tree branches or leaves

Fungi �Examples caused by bacteria or fungi are Powdery mildew Blights Canker Rots Wilts Smut

Virus �Viruses are pathogens with an extremely narrow host range and are usually a threat to crops �Examples caused by viruses, bacteria, or fungi are wilts and blights

Tobacco Mosaic Virus �Attacks tomatoes, pepper, poinsettias, and tobacco �Can be transferred from human hands of a smoker Be sure to wash your hands before working with plants to control the spread of this virus �Cause leaves to have irregular mottled areas with patterns ranging from dark to light green and yellow to white

Tobacco Mosaic Virus

Additional Information �Parasitic Plants attach to host plants Mistletoe Dodder Lichens �Plant diseases must be identified before they can be treated

Additional Information �Warm temperatures and moist conditions in greenhouse plant production make most plant diseases worse because of environmental conditions that support disease causing pathogens �Preventing plant diseases is better than treating the diseases.