BASIC PLANT

PATHOLOGY

Dr. Monica ElliottFt. Lauderdale REC

WHAT IS A

HEALTHY PLANT?

You can’t diagnose a plant problem without knowing how the plant looks when healthy!

PLANTS DON’T TALK!

Information about a plant sample must come from person managing the plant !

Ask the right questions!

Abioticvs.

Biotic

But, first rule out those pesky

insects

Sooty mold is a fungus, but not a pathogen. It is feeding off insect

excretions, such as honeydew.

Abiotic• Injuries• Disorders• Pathogen is not causing problem

Biotic• Pathogen is the problem

INJURY

A destructive physical occurrence to the plant

INJURY

• Lightning strikes, Tire tracks• Car or lawn equipment exhaust• Animals - moles, armadillos, urine

NO pathogen!

DISORDERInteraction between the plant &its environment that is usuallyassociated with imbalances of physical or chemical require-ments for plant growth.

DISORDERS

• Cold or heat stress• Nutritional, usually deficiencies• Air pollution • Excessive rainfall or drought• Pesticide phytotoxicity

NO pathogen!

Cold Damage

DroughtOedema

Both too much and too little water can cause disease-like symptoms.

Sunburned palm leaf

Manganese deficiency

Manganese deficiency

Potassium deficiency

SPOTS & PATCHES

•A plant with a spot does not automatically mean it has a disease.•A yellow or dead patch in the lawn does not mean there is a disease.

Chinchbug damage

Typical injury from growth regulator type herbicide

DISEASE Interaction between the plant and a pathogen that disruptsthe normal growth andappearance of the plant.

DISEASEThree Components:

• Susceptible host• Virulent pathogen• Conducive environment

Disease Triangle

Types of Pathogens • Fungi• Bacteria• Phytoplasmas (mlo)• Viruses• Viroids

large

small

Most bacteria can be cultured on

artificial media.

Phytoplasmas, viruses and viroids cannot be cultured

on media.

Most fungi can be cultured on artificial media, but not all.

PATHOLOGY TERMS • MYCELIA: thread-like material that is body of fungus.

• SPORES: reproductive structures of a fungus or bacterium

• Bacteria – most enter through natural openings or wounds

• Viruses – transmitted through wounds made mechanically or by vectors

• Phytoplasmas – transmitted by vectors

• Fungi – enter through natural openings, wounds; or by mechanical pressure or enzymes they produce

FUNGUS - FUNGI • No chlorophyll, so no self energy• PATHOGEN: obtains energy from living things• SAPROPHYTE: obtains energy from dead things• SAME fungus can be BOTH a pathogen and a saprophyte!

PATHOLOGY TERMS• SYMPTOMS: how plant expresses

the fact it has a diseaseleaf spots, patches, tip die back, etc.

• SIGNS: actual pathogen parts associated with a diseased plant

spores, mycelia, conks, mushrooms

Signs of Disease

Signs of Disease

Signs of Disease

Disease

Symptoms

Plant

Organs

And

Functions

Symptoms

• spot – small, distinct lesion on leaf, fruit . . .

• blight – spots that have coalesced or merged together; more tissue being affected

• rot – tissue is breaking down (fruit, roots); usually mushy, but can be dry

• wilt – plant droops due to water stress; can be systemic (xylem) or due to root rot

Symptoms

• gall – masses of undifferentiated growth; usually on stems or woody tissue

(branches) but can be on roots - wart, clubroot, witches’-broom

• canker – sunken lesions; usually on stems or woody tissue• patches, decline – terms often used in association with grasses (turf, grain crops)

Symptoms Caused by Bacteria• leaf spots and blights – water soaked, greasy

• soft rots of fruits

• wilts (systemic – xylem)

• gall (overgrowths/cell proliferation)

• cankers

Symptom:Water soaked or greasy leaf spots

Symptom:Water soaked or greasy leaf blight

Symptom:Wilt

Symptom:Gall

Symptoms Caused by Viruses• dwarfing or stunting to some degree

• mosaics – light green, yellow or white areas intermingled with green – leaves or fruits

• ring spots – chlorotic or necrotic rings – leaves, fruits or stems

• are always systemic infections

Symptom:Dwarfing and Stunting

Symptom:Mosaic

Symptom:Ringspot

Symptoms Caused by Fungi• leaf spots and blights (including rust and powdery mildew)• soft or dry rots of fruits, bulbs . . .• root rots • wilts (systemic – xylem)• overgrowths/cell proliferation – clubroot, galls, warts, witches’-broom• scabs, cankers, patches and decline

Symptom:Leaf spots and blight

Symptom:Soft or dry rots

Symptom:Wilt

Symptom:Patches and Decline

PATHOLOGY TERMS• PATHOGENESIS: the pathogen either

does or does not cause a disease yes or no question

• VIRULENCE: severity level of thedisease that a pathogen causes minimal damage vs. dead plant

Plant Samples• Goal is to have plant sample arrive in diagnostic laboratory looking like it did in the field or landscape.

• Keep roots moist, but do not place any other tissue inside plastic bag.

• Ask the right questions, fill out form completely. It is critical to have background information about the situation.

Plant Samples• Ask the right questions:

1) What is the plant?

2) Where is plant growing?

3) Is this sample typical?

4) When did symptoms appear?

5) Fertility and pesticide applications?

Plant Samples

Plant Samples• Best samples are those that exhibit progression of symptoms – e.g., leaf spot to leaf blight to severely diseased plant.

• Best to examine entire plant, if possible, as root disease could be cause for leaf symptoms

• Good pictures are useful, illustrating overall symptoms and close-ups

Plant Samples

• Soil samples for disease diagnosis are useless.

• Do not be afraid to tell a client that the sample is inadequate. We are not miracle workers!

• It is better to make no diagnosis than to make the wrong diagnosis, especially if it is a valuable specimen or pesticides are required.

Three “Little” Steps

1. Identify the disease.

2. Identify the conditions causing disease diagnosed.

3. Identify the management techniques that will alter the disease-conducive conditions causing disease diagnosed.

SureLook Holmes

DISEASEThree Components:• Susceptible host• Virulent pathogen• Conducive environment

Disease Triangle

Plant Disease Control

Integrated Approach

• Pathogen exclusion or sanitation

• Plant resistance (genetic)

• Cultural methods

• Chemical methods

Plant Disease Control

• Pathogen exclusion

- via regulation

- via ‘just don’t bring it home no matter how cute it looks’ if it has a spot, wilt, etc.

Plant Disease ControlPlant resistance (genetic)

• Immunity is the rule in the plant kingdom

• Where immunity does not exist, plant breeders have developed cultivars with resistance to specific pathogens.

Plant Disease Control

• Plant resistance (genetic)

Plant Disease Control

• Plant resistance (genetic)

- breeding for resistance to pathogen

- plant adaptation to site (right plant for the right site concept)

- monoculture vs. mixed culture

Plant Disease Control

• Cultural methods

- crop rotation

- host eradication (alternate hosts)

- improved plant environment, especially water management

Plant Disease Control

• Cultural methods

- sanitation of

tools, pots, shoes,

equipment, etc.

Plant Disease Control

• Chemical methods

- seed treatments

- soil treatments/root drenches

- foliar sprays

- trunk injections

Plant Disease Control• Chemical methods

- critical to understand that chemicals do not necessarily eliminate symptoms observed

- most chemicals prevent disease from ever occurring or keep it from spreading

Plant Disease Control• Chemical methods

- ex: leaf spots don’t disappear, but old leaves with spots die and new growth is healthy and spot free

- ex: rotted roots eventually die, but new roots are healthy and take their place to supply water and nutrients

Plant Disease Control• Chemical methods

“The label is the law.”

Pesticide labels must be followed, even by homeowners – safety to applicator and environment.

The site for application must be on the label – turf vs. ornamentals.

Plant Disease Control

Some diseases do not have ANY control

methods.

Proactive vs. Reactive

The single best method for controlling diseasesis to prevent them!