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 YellowsActs 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