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Plant Diseases • A disease is defined as any type of injurious abnormality • A pathogen is any biological agent that causes an injurious abnormality Plant diseases • There are 4 types of commonly recognized pathogens – Virus – Bacteria – Fungi – nematodes Signs and Symptoms • Symptom is the plants response to attack by a pathogen • Sign is structures produced by the organism ( spore producing structures, mycelium) Virus Tobacco Mosaic Virus TMV TMV Virus symptoms • Unthrifty plants – Slow to grow – Mosaic light spots and stripes Aster Yellows Acts like a virus but is a mycoplasma Virus indexing • If you are buying cloned plants they will often say Virus Indexed. • That means they are tested and proven to be virus free. • very important when buying raspberry plants or strawberry plants Bacteria- fire blight Fire Blight Bacterial symptoms • Rapid spread, can be spread by wind or insects,humans • Soft rots producing snotty oooz • Can be really smelly Fungi Botrytis – Grey Mold Fungus Fungus • Signs: mycelium, fruiting bodies • Symptoms: necrotic areas, wilt when fungus attacks the roots • Phloem blockage, xylem blockage Nematodes • Root Knot Nematode Nematodes • Feed on roots and allow secondary infections • Cause small tumors on roots • Damage to plants by fungi bacteria and nematodes can be classified in 3 types – Direct damage by feeding – Toxins injected into the plant – From secondary infections that enter via the physical damage caused by the primary agent Crop infesting diseases are troublesome because they will continue to reproduce and feed UNTIL • 1. The food is used up • 2. the environment becomes unfavorable • 3. they are destroyed by some predator/ disease Disease transmission • • • • • Water is necessary for fungus infection Insects Humans Infected seed Infected soil – brought in on shoes or tractor tires Curing or avoiding plant disease? • Any of the previous factors can be interrupted • Cultural control – Roguing, sanitation, plowing plant refuse under, stirring the soil to expose egg masses, keep plants healthy, avoid smoking, regulate pH, hot water treatment of seed, • Chemical control What are those letters? • • • • • • • · · · · · · · V Verticillium Wilt Virus F Fusarium Wilt Virus N Nematodes T, TMV, ToMV Tomato Mosaic Virus BSK Bacterial Speck ST Stemphyllium (Grey Leaf Spot) FCR Fusarium Crown Rot
