Plant Diseases Objective 8 02 Discuss diseases and

Plant Diseases

Objective 8. 02 • Discuss diseases and viruses.

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

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

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

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

Blight

Leaf Spots

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. • 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.

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

Damping Off

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

Rust

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

Gall • Swellings or growths on plants

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