Transcript What is a healthy plant?
BASIC PLANT PATHOLOGY
Dr. Monica Elliott Ft. 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!
Abiotic vs.
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.
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Abiotic
Injuries Disorders Pathogen is not causing problem
Biotic
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Pathogen is the problem
INJURY A destructive physical occurrence to the plant
INJURY
NO pathogen!
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Lightning strikes, Tire tracks Car or lawn equipment exhaust Animals - moles, armadillos, urine
DISORDER
Interaction between the plant & its environment that is usually associated with imbalances of physical or chemical require ments for plant growth.
DISORDERS
NO pathogen!
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Cold or heat stress Nutritional, usually deficiencies Air pollution Excessive rainfall or drought Pesticide phytotoxicity
Cold Damage
Oedema Drought Both too much and too little water can cause disease-like symptoms .
Sunburned palm leaf
Manganese deficiency
Manganese deficiency
Potassium deficiency
SPOTS & PATCHES
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A plant with a spot does not automatically mean it has a disease.
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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 disrupts the normal growth and appearance of the plant.
DISEASE
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Three Components: Susceptible host Virulent pathogen Conducive environment Disease Triangle
Types of Pathogens
large small
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Fungi Bacteria Phytoplasmas Viruses Viroids (mlo)
Phytoplasmas, viruses and viroids cannot be cultured on media.
Most bacteria can be cultured on artificial media.
Most fungi can be cultured on artificial media, but not all.
PATHOLOGY TERMS
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MYCELIA: thread-like material that is body of fungus.
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SPORES: reproductive structures of a fungus or bacterium
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Bacteria – most enter through natural openings or wounds
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Viruses – transmitted through wounds made mechanically or by vectors
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Phytoplasmas – transmitted by vectors
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Fungi – enter through natural openings, wounds; or by mechanical pressure or enzymes they produce
FUNGUS - FUNGI
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No chlorophyll, so no self energy PATHOGEN: obtains energy from living things
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SAPROPHYTE: obtains energy from dead things
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SAME fungus can be BOTH a pathogen and a saprophyte!
PATHOLOGY TERMS
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SYMPTOMS: how plant expresses the fact it has a disease leaf spots, patches, tip die back, etc.
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SIGNS: actual pathogen parts associated with a diseased plant spores, mycelia, conks, mushrooms
Signs of Disease
Signs of Disease
Signs of Disease
Plant Organs And Functions Disease Symptoms
Symptoms
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spot – small, distinct lesion on leaf, fruit . . .
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blight – spots that have coalesced or merged together; more tissue being affected
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rot – tissue is breaking down (fruit, roots); usually mushy, but can be dry
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wilt – plant droops due to water stress; can be systemic (xylem) or due to root rot
Symptoms
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gall – masses of undifferentiated growth; usually on stems or woody tissue (branches) but can be on roots - wart, clubroot, witches’-broom
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canker – sunken lesions; usually on stems or woody tissue
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patches, decline – terms often used in association with grasses (turf, grain crops)
Symptoms Caused by Bacteria
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leaf spots and blights – water soaked, greasy
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soft rots of fruits
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wilts (systemic – xylem)
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gall (overgrowths/cell proliferation)
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cankers
Symptom: Water soaked or greasy leaf spots
Symptom: Water soaked or greasy leaf blight
Symptom: Gall Symptom: Wilt
Symptoms Caused by Viruses
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dwarfing or stunting to some degree
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mosaics – light green, yellow or white areas intermingled with green – leaves or fruits
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ring spots – chlorotic or necrotic rings – leaves, fruits or stems
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are always systemic infections
Symptom: Dwarfing and Stunting
Symptom: Mosaic
Symptom: Ringspot
Symptoms Caused by Fungi
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leaf spots and blights (including rust and powdery mildew)
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soft or dry rots of fruits, bulbs . . .
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root rots
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wilts (systemic – xylem)
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overgrowths/cell proliferation – clubroot, galls, warts, witches’-broom
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scabs, cankers, patches and decline
Symptom: Leaf spots and blight
Symptom: Soft or dry rots
Symptom: Wilt
Symptom: Patches and Decline
PATHOLOGY TERMS
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PATHOGENESIS: the pathogen either does or does not cause a disease yes or no question
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VIRULENCE: severity level of the disease that a pathogen causes minimal damage vs. dead plant
Plant Samples
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Goal is to have plant sample arrive in diagnostic laboratory looking like it did in the field or landscape.
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Keep roots moist, but do not place any other tissue inside plastic bag.
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Ask the right questions, fill out form completely. It is critical to have background information about the situation.
Plant Samples
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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
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Best samples are those that exhibit progression of symptoms – e.g., leaf spot to leaf blight to severely diseased plant.
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Best to examine entire plant, if possible, as root disease could be cause for leaf symptoms
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Good pictures are useful, illustrating overall symptoms and close-ups
Plant Samples
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Soil samples for disease diagnosis are useless.
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Do not be afraid to tell a client that the sample is inadequate. We are not miracle workers!
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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.
SureLook Holmes 3. Identify the management techniques that will alter the disease-conducive conditions causing disease diagnosed.
DISEASE
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Three Components: Susceptible host Virulent pathogen Conducive environment Disease Triangle
Plant Disease Control Integrated Approach
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Pathogen exclusion or sanitation
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Plant resistance (genetic)
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Cultural methods
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Chemical methods
Plant Disease Control
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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 Control Plant resistance (genetic)
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Immunity is the rule in the plant kingdom
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Where immunity does not exist, plant breeders have developed cultivars with resistance to specific pathogens.
Plant Disease Control
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Plant resistance (genetic)
Plant Disease Control
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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
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Cultural methods - crop rotation - host eradication (alternate hosts) - improved plant environment, especially water management
Plant Disease Control
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Cultural methods - sanitation of tools, pots, shoes, equipment, etc.
Plant Disease Control
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Chemical methods - seed treatments - soil treatments/root drenches - foliar sprays - trunk injections
Plant Disease Control
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Chemical methods
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critical to understand that chemicals do not necessarily eliminate symptoms observed
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most chemicals prevent disease from ever occurring or keep it from spreading
Plant Disease Control
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Chemical methods
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ex: leaf spots don’t disappear, but old leaves with spots die and new growth is healthy and spot free
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ex: rotted roots eventually die, but new roots are healthy and take their place to supply water and nutrients
Plant Disease Control
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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 diseases is to prevent them!