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 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.

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

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

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

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

Mosaic

Others Diseases

Canker Causes open wounds on woody plants

Canker

Rots Cause plant to decay and die

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

Smut

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

Wilt