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10/31/2013
1
Richard J Buckley, PDL Director
Soil Testing and Plant
Diagnostic Services
MG Training:
Basic plant
pathology and
the art of the
diagnosis.
www.njaes.rutgers.edu/services
What is “plant pathology”?
• Plant pathology is the study of:
– living entities and environmental
conditions that cause disease in plants
– mechanisms by which these factors result
in disease
– interactions between disease agents and
hosts
– disease prevention and management
History of plant pathology
• Theophrastus (c. 300 B.C.): Greek philosopher
who believed that God controlled the weather
and brought about disease; diseases were the
manifestation of the Wrath of God
• Concept of spontaneous generation: diseases
(human and plants) develop spontaneously
• Even after advent of the microscope, the
microbes observed were thought to be the
result of the disease, not the cause of it
History of plant pathology
• In 1845, late blight of
potato epidemics
occurred in Belgium,
Holland, Germany,
Switzerland, France,
Italy, England, Ireland,
and Scotland
• Completely destroyed
the potato crop in
Ireland in 1845-1846
(Irish potato famine)
Anton deBary: the father of plant pathology
• In controlled
experiments, proved
that a fungus causes
late blight (1861)
• Fungus was named
Phytophthora infestans
(Phyto = plant; phthora
= destroyer)
Anton deBary (APS)
Irish potato famine (1845-46)
• Gave birth to the science of plant pathology
• Changed the course of human history
• Introduces:
– The political aspects of the food supply
– Risks of genetic uniformity in crops
– Problems when new crops are distributed
throughout the world
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Plant Pathology 101
• Plant Disease:
–any disturbance of a plant that
interferes with its normal structure,
function, or economic value, or
–any condition of a plant that is
contrary to grower expectations
Plant Pathology 101
• Plant Disease: a condition of abnormal physiology in a
susceptible host plant that is a result of
the plants constant association with a
disease causing agent within a set of
favorable environmental conditions.
Plant Pathology 101
Host Plant Condition
• Most plants resist or tolerate attack
• Plant must be susceptible to attack
• Resistance and susceptibility different
degrees of the same thing
influenced by genetics
influenced by environment
• Immunity is absolute
Two types of causal agents:
1. Biotic (infectious)
– organism (pathogen) grows, multiplies,
and spreads to other plants
– 10% of diseases reported
2. Abiotic (non-infectious)
– environmental conditions that impact
plant development (physiogens)
– much more common: 90% of diseases
reported (injury not disease)
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Abiotic Causal Agents - Physiogens
• Physical factors
temperature
moisture
• Chemical factors
air pollutants
pesticides
fertilizers and salts
• Mechanical factors
everything else
Biotic Causal Agents - Pathogens
• Fungi (largest group of plant pathogens)
• Prokaryotes (no nuclear membrane)
– bacteria
– mollicutes (phytoplasmas, spiroplasmas)
• Nematodes (round worms)
• Viruses (nucleic acid with a protein coat)
• Viroids (naked RNA with no protein coat)
• Parasitic plants
• Algae
• Protozoa
• Insects and mites
Fungi
• Systematic study of fungi is 250 years old
• Mycology is Greek for mycos (fungus) + -logy (study of)
• Manifestations of this group of organisms is thousands
of years old (e.g., wine and leavened bread)
• Most important as agents of decay
• Can attack wood products, leather goods, fabrics,
petroleum products, foodstuffs
• Infect animals and plants: most common (or important)
of plant pathogens
Cottony mycelium of Pythium
Photo: APS Press
Pythium Disease Complex
Bacteria
• 1600 species are known, most are saprophytic
• Important as decomposers and in nitrogen recycling
• Cause human, animal (e.g., tuberculosis, pneumonia,
typhoid fever), and plant diseases
• Actinomycetes produce antibiotic compounds
• Shapes: rod, spherical (cocci), spiral, or filamentous
• Reproduce by fission (they divide in two)
Xylella fastidiosa - a single-celled bacterium with
rippled cell walls
Bacteria
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http://www.sciencenetlinks.com/images/interactive/bacteria.gif
Bacteriology 101
Bacteria are found in every ecological niche
Large colonies form a biofilm: an extracellular polysaccharide ooze
Bacteriology 101
Pathogenic bacteria are found on their hosts
Infection occurs through natural openings or wounds
Large populations overwhelm plant defenses and invade xylem tissues
Plant tissues are killed and digested by toxins and enzymes
Photo: APS PressIllustration by Samatha Bozak
Virus
• entity that contains genetic material within a protein coat
that can only reproduce using the metabolic processes of
a suitable host cell
– Structure
• Protein coat = capsid
• Nucleic acid core (DNA or RNA) = nucleocapsid
– Size
• Ultramicroscopic = too small for microscope
• Must use electron microscope
– Shape
• Rod, filamentous, isometric
• May have more than one particle – satellites
Tobacco Mosaic Virus
Photo: APS Press
Nematode
• Kingdom Animalia; non-segmented roundworms
• Several thousand species
• Most live in fresh or salt water, feeding on
microorganisms and microscopic plants and animals
• Numerous species attack animals
• Several hundred species feed on living plants (roots
or foliar tissue), obtaining food with stylets
• Annual losses on crops such as grains, legumes,
banana, cassava, coconut, potato, sugar beet,
sugarcane, and sweet potato are approximately 11%
Plant parasite
Plant parasitic nematodes have a stylet
Photo: Richard Buckley, NJAES
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Parasitic Plants
• Epiphyte – orchid, spanish moss
• Hemi parasite – mistletoe
• True parasite – dodder, witchweed, dwarf mistletoe
Biotic Causal Agents
dodderPhoto: Richard Buckley, NJAES
• Pathogen must be present
• Pathogen must be pathogenic
• Pathogen must be virulent
influenced by genetics
influenced by environment
Causal Agent
Photo: Dr. Peter Dernoeden, UMD
Environmental Condition
• Provides pathogen opportunities
influences host plant condition
increases pathogen virulence
• Predisposing conditions
site
weather
management
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Recognizing Diseases
• Symptoms -
observable condition of abnormal physiology in the plant
• Signs -
physical presence of the causal agent or clear evidence of abiotic stress factors
Symptom descriptions
leaf spot, blight, tip blight,
dieback, flagging, chlorosis,
necrosis, canker, wilt, root rot,
witches broom, mottling,
interveinal necrosis, epinasty,
scorch, crown rot, defoliation,
boring phyllody, leaf blotch, rust,
damping off, soft rot,
mummification, stem pitting, gall,
shot-hole, bleeding, slime flux,
blast, scald, bronzing, staghead,
tumefacation, fasciation, hairy
root, knots, enation, shoestring,
erinos, stipple, notching,
chewing, skeletonization, rugose,
puckering, edema, intumescence,
russet, scab, callus, leafroll, leaf
curl, croziers, dwarfing, stunting,
rosetting, atrophy, etiolation,
spiralism, hyperelongated,
bunchy, cresting, dead
Photo: APS Press
Blight, dieback
Photo: Dr. Ann Gould, NJAES
Aster yellows
Symptoms: stunting
chlorosis
phyllody
witches broom
Photo: Sabrina Tirpak, NJAES
Photo: Dr. Joe Peterson, Rutgers
• larvae leave distinct galleries
Photo: Richard Buckley, NJAES
Pine Bark Beetle Wilt symptom = cause?Photo: APS Press
10/31/2013
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Symptoms
• Caution
Not the be all – end all
Simple starting point
Don’t jump to conclusions
Need more information
Signs
Fruiting body, sporocarp,
cliestothecia, pycnidia,
mushroom, hyphae,
stroma, spores, conidia,
sclerotia, conidiophore,
perithecia, apothecia,
synnema, cyst, egg, cast
skin, nematode, insect,
plasmodium,
sporodochia, acervulus,
aecium, oospore,
zoospore, cirrhus,
basidiocarp, ascus,
sporangium, teliospore,
uredium
Photo: APS Press
Photo: Richard Buckley, NJAESPhoto: APS Press
Cedar Apple Rust
• telia on Eastern red cedar
Photo: Richard Buckley, NJAES
Dogwood Anthracnose
The fungus moves into small stems and causes dieback
Photos: Dr. Ann Gould, NJAES
Discula destructa
Acervulus with conidia
Photos: Dr. Ann Gould, NJAES
Signs
• Caution
Not the be all – end all
Simple starting point
Don’t jump to conclusions
Need more information
10/31/2013
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Pestalotiopsis spp.
Gray Leaf Blight
Photos: APS Press
Winter desiccation – March 2010
Photos: Richard Buckley, NJAES
Winter injury
Basic Diagnostics 101
1. Identify the plant
2. Observe the symptoms
3. Evaluate the predisposing conditions
4. Identify the sign
5. Synthesize the information
Step 1: Identify the plant
• Understand the needs of the plant
What are the horticultural requirements?
• Provides a list of pathogens
Key plant / key pest concept
Zoysia turns brown in winter in stark contrast to the perennial ryegrass
Photo: Richard Buckley, NJAES
• Fungus - Volutella buxi
Volutella Stem Blight
• Host - Boxwood
Photo: Richard Buckley, NJAES
10/31/2013
9
Proper identification is key
Understand the needs of the plant
What are the horticultural requirements?
Know your plant materials!
Photos: Richard Buckley, NJAES
Step 2: Observe symptoms
• Define the problem
Examine the entire plant
Examine the plant community
Recognize patterns
Observe symptom progression
Recognize classic symptom expression
Step 2: Observe symptoms
• Define the problem
Examine the entire plant
Photo: APS Press
Examine the entire plant
Photo: University of California
Evaluate the entire plant
Photos: Richard Buckley, NJAES
Lesser Peachtree Borer Botryosphaeria Canker
Photos: Debbie Miller, Davey Tree
Don’t be afraid to cut it up!
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Define the problem!
Identify dysfunctional plant part or plant system
What kind of symptoms do you see?
Photos: Richard Buckley, NJAESStep 2: Observe symptoms
• Define the problem
Examine the entire plant
Examine the plant community
Symptom Expression
Similar symptoms on
unrelated plants
are likely due to a
non-living (abiotic) cause
Similar symptoms on
related plants
are likely due to a living
(biotic) organism
Photo: University of California
Step 2: Observe symptoms
• Define the problem
Examine the entire plant
Examine the plant community
Recognize patterns
Recognize Patterns
• Uniform - abiotic
• Random - biotic
Drop Spreader Disease
What can you say about this?
Photo: Richard Buckley, NJAES
10/31/2013
11
Close shearing
Photo: Richard Buckley, NJAES
Crown and Root Rot
Photo: APS Press
Drought stress
Photo: Dr. Ann Gould, NJAES
Bacterial Leaf Scorch
Photo: Dr. Ann Gould, NJAES
Step 2: Observe symptoms
• Define the problem
Examine the entire plant
Examine the plant community
Recognize patterns
Observe symptom progression
Observe symptom progression
• Progressive – biotic
• Non-progressive - abiotic
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Crown and Root Rot
Photo: Richard Buckley, NJAES All plants rapidly decline after a week above 100oF
Photo: Richard Buckley, NJAES
Heat stress
Step 2: Observe symptoms
• Define the problem
Examine the entire plant
Examine the plant community
Recognize patterns
Observe symptom progression
Recognize classic symptom expression
Typical symptoms of fungal pathogens
Fungi cause most plant diseases
Fungi attack all plant parts and cause all
possible symptoms
Central infection point
Rounded, even borders
Discolored margins
Dry rot
Signs frequently produced
• Fungus – Entomosporium mesculi
Entomosporium Leaf Spot
• Host – 60 species in the rosaceae
Photo: Richard Buckley, NJAES
Photo: Richard Buckley, NJAES
Crown and Root Rot
Photos: Richard Buckley, NJAES
particular pathogens attack particular plant parts
Note: dry rot, discolored cambium, even border
10/31/2013
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Maple Anthracnose
Photos: Sabrina Tirpak, NJAES
• Fungus – Aureobasidium apocrypta
• Host – sugar and red maplesNote: the gelatinous amber colored acervuli
Nectria Canker
Central Infection Point
Concentric circles
Rounded border
Discoloration of sapwood
Dry rot
SignsPhoto: Dr. Ann Gould, NJAES
Typical symptoms of bacterial pathogens
Bacteria attack all plants, but are most common on herbaceous hosts
Infection through natural opening or wound
Angular borders
Chlorotic halo
Water soaked rot
Tissue blight
Rotten smell
Bacterial Leaf Spot
Photo: Sabrina Tirpak, NJAES
Fire Blight
Bacteria ooze from natural openings on infected trees
Photo: APS Press
Fire Blight
Pollinators carry bacteria to nectar cells in flowers, which results in “spur blight”
Photo: APS Press
10/31/2013
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Fire Blight
“Spur blight” progresses to branch blight
Photo: APS Press
Fire Blight
Severe disease
Photo: Richard Buckley, NJAES
Photo: APS Press
Erwinia Soft Rot
Photo: Richard Buckley, NJAES
Bacterial Blight of Cucurbit
Photo: Richard Buckley, NJAES
Typical symptoms of viral pathogens
Virus attack many plants and cause
unusual symptoms
Abnormal growth
Abnormal color
Look for the vector
Latent / symptomless host
Rose Mosaic Virus
Photos: APS Press
10/31/2013
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Rose Mosaic Virus
Photos: APS Press
Rose Mosaic Virus
Photos: APS Press
Impatiens Necrotic Spot
Photo: Richard Buckley, NJAES
Impatiens Necrotic Spot
Photo: Sabrina Tirpak, NJAES
Impatiens Necrotic Spot
Photos: APS Press
Western flower thrips
adult
larva
Virus Vectors
Photos: APS Press
Photo: Dr. Ann Gould, NJAES
10/31/2013
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Typical symptoms of physical injury
• Tip and edge scorch
– On individual plant parts
– On entire plant canopy
• Intervienal necrosis
• Loss of older needles
• Early fall color
• Premature defoliation
Loss of turgor first symptoms of drought
Drought stressPhoto: Ann Gould, NJAES
Tip and edge
scorch
Tip and edge scorch due to drought
Drought stressPhoto: University of California
Needles wilt and scorch too
Photos: Bruce Clarke, NJAES
Drought stress
Severe scorch after high heat stress
Photos: Richard Buckley, NJAES
Heat stress
tip and edge scorch
over entire plant
top - down injuryPhoto: Richard Buckley, NJAES
Photo: University of California
Drought stress
10/31/2013
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Damage is more severe on tough sites – July 11, 2010
Photo: Richard Buckley, NJAES
Heat stress
Typical symptoms of chemical injury
• Symptom follows application pattern
– Patterns match application technique
– Cause and effect clearly evident
• Symptom expression relates to product:
– Toxic contact with exposed plant parts
– Uptake and translocation of toxic concentrations
Typical symptoms of chemical injury
• Necrosis of exposed plant parts
– due to direct contact with toxin
• Abnormal growth and color
– due to growth-regulator effects
– due to imbalances of nutrients
• Top-down, outside-in, tip-edge
– due to uptake of toxin
– on individual plant parts
– on entire plant canopy
Ozone toxicity
Photo: APS Press
Ozone causes tan, gray or metallic spots on upper leaf
surfaces during hot, sunny days in summer
Sulfur dioxide toxicityPhoto: APS Press
Sulfur dioxide is absorbed through the stomates in toxic concentrations;
damage was due to a poorly functioning heater and the plants recovered Burn from horticultural oil application on cloudy day
Oil phytotoxicityPhoto: Sabrina Tirpak, NJAES
10/31/2013
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Injury to new growth due to Imprelis;
Do not apply under the drip-line!
Herbicide phytotoxicity
Photo: Sabrina Tirpak, NJAES
dicamba distorts flowers and causes upward
cupping of leaves; this sample injured by drift
Herbicide phytotoxicity
Photos: Richard Buckley, NJAES
Salt phytotoxicity
De-icing salt damage – burn by contact
Photos: A&L Services
Sodium and chloride are absorbed and moved to the
leaf tips where they build to toxic concentrations
Photo: APS Press
Salt phytotoxicity
Boron toxicity
Photo: APS Press
Irrigation with high boron content water is also problematic
Phosphorous deficiency
Photo: APS Press
P deficiency rare in most NJ soils;
symptoms include purple discoloration
10/31/2013
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Iron deficiency
Photos: Richard Buckley, NJAES
High pH binds Fe in the soil and causes deficiency symptoms
Liquid fertilizer overdose
Typical symptoms of mechanical injury
• Breaks
• Bruises
• Punctures
• Cracks
• Chewing
• Girdling
• Root pruning
Lightning strike
Winter Injury
Heavy snow breaks branches and knocks stuff over
Photo: Richard Buckley, NJAES
Winter Injury
Ice will do it too – January 1993
Photo: A&L Services
Photo: Richard Buckley, NJAES
10/31/2013
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Root damage
Damage to
the rootzone
= damage to
the canopy
Root damage
Photo: Ann Gould, NJAES
Do no construction under the drip line
String girdling
Photo: Ann Gould, NJAES
Stop sign
Step 3: Evaluate the predisposing conditions
• Analyze the site condition
• Record the weather condition
• Evaluate management program
Step 3: Evaluate the predisposing conditions
• Analyze the site
Drainage
Shade and exposure
Air movement
Contour
Soil chemical properties
Soil physical properties
10/31/2013
21
Some wet sites are obvious
Note the white pine performs poorly on wet sites
Photo: University of California
Wet feet
Taxus does poorly on wet sites
Photo: Richard Buckley, NJAES
Wet feet
Damage most severe on exposed surfaces (NE side)
Winter injury Pachysandra Stem Blight
Photo: Richard Buckley, NJAES
Black Layer
Black layer – smells like a swamp, must be a swamp
Photo: Richard Buckley, NJAES Weed indicators of site conditions
High pH = plantain Low pH = sorrel
10/31/2013
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Step 3: Evaluate the predisposing conditions
• Record the weather condition
Temperature
Relative humidity
Rainfall
Evapotranspiration rates
Air quality
Time of year
Entomosporium Leaf Spot
severe disease on photinia
Photo: Richard Buckley, NJAES
Photo: Richard Buckley, NJAES
Nectria Canker
Photo: University of California
Rhizoctonia solani Predictive Model
• Warm nights
– Soil temperature >61oF
– Air temperature >59oF
• Extended leaf wetness
– 95% RH for >10 hours
– 0.1” rain or irrigation in
preceding 36 hours
Brown Patch
Photo: Richard Buckley, NJAES
Leaf scorch and drop after high heat – July 11, 2010
Photo: Richard Buckley, NJAES
Heat stress Frost damage
Cold temperatures
damage new
growth
Cause and effect
clearly evident
10/31/2013
23
Wet Feet and Wind
Note the lack of root biomass and the poor drainage
Photo: Richard Buckley, NJAES
Step 3: Evaluate the predisposing conditions
• Evaluate management program
Pruning
Fertility
Irrigation
Cultivation
Pesticide input
Wet roots turn black
Wet feet
Photo: Bruce Clarke, NJAES
Excessive mulch
Photo: University of California
Cupressaceae very hard hit by heat(Poor planting technique, crummy mulch, and excess irrigation didn’t help much)
Photos: Richard Buckley, NJAES
Physical injury Herbicide phytotoxicity
Distorted growth = phenoxy herbicide
damage
Photo: University of California
10/31/2013
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What fungicides, insecticides, and
herbicides were used on site?
How much and when?
Specific chemicals cause specific
problems – Can the materials used
cause the symptoms you see?
Photo: Richard Buckley, NJAES
Chemical Injury
Step 4: Identify the sign
• Macroscopic observation
• Insect traps
• Microscopic observation
• Pathogen stimulation
• Pathogen isolation
• Antibody based test kits
• Special tests
Bagworm
• epidemicPhotos: Richard Buckley, NJAES
pseudosclerotia “Red threads” form on leaf tips
Red Thread
Photo: Richard Buckley, NJAES
Macroscope
10 to- 60x
magnification
Juniper Tip Blight
Phomopsis spp.
pycnidia
10/31/2013
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Oriental beetle, Exomala orientalis
Raster patterns indicate scarab species
Nematodes from turf soil
Compound
microscope
40 to- 400x
magnification
Copper Spot – Gloeocercospora sorgii
Note: sporodochia produce copious numbers of whip-like conidia
Photo: Richard Buckley, NJAES
Bacterial streaming
Bacteria
Photo: Sabrina Tirpak, NJAES
Pink Snow Mold
Microdochium nivale
incubate plugs
to stimulate fungus
Photo: Richard Buckley, NJAES
10/31/2013
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Cyclamen Wilt
Bacteria laden “sterile” water is then streaked on media:
Which one is the pathogen?
Photo: Lane Tredway, NC State
Bacteriology 101
selective media
differential media makes target look different
Bacteriology 101
Photos: APS Press
only allows target to grow
Isolates are subjected
to a battery of
biochemical tests
Plant Pathology 101
Antibody-based test kits effective for Pythium
Photo: Sabrina Tirpak, NJAES
Detection
PCR ELISA
Plant Pathology 101
Photo: Dr. Ann Gould, NJAES Photo: Sabrina Tirpak, NJAES
Step 5: Synthesize the information
• Put it all together
Evaluate the symptoms
(host)
Consider the
predisposing factors
(environment)
Identify the sign
(causal agent)
10/31/2013
27
!!!! Caution !!!!
• Fungi don’t read the book
• Don’t jump to conclusions
• Keep an open mind
• Expect the unexpected
• Accumulate information
• Educate yourself
• Act on your hunches
Soil Testing and Plant
Diagnostic Services
www.njaes.rutgers.edu/services