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8/3/2019 Diagnosing Plant Problems-Plant Diseases
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National Plant Diagnostic Network
National Plant Diagnostic Network
Diagnosing PlantProblems: Plant
DiseasesNational Plant Diagnostic Network
First Detector Training
Williamson, Riley, and Maloy. December 2006.
Update, August 2008.NPDN Publication No. 0013
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MODULE 4Diagnosing plant problems: Plant Diseases
Adapted from Plant Disease
Diagnosis by M. B. Riley, M.
R. Williamson and O. Maloy.In: The Plant Health Instructor.DOI:10.1094/PHI-I-2002-1021-01
Used by permission of the American Phytopathological Society
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MODULE 4Diagnosing plant problems: Plant Diseases
Plant Problem DiagnosisDiagnosisprocess used for the
identification of problems.Tools:
Plant sciences, especially plant
pathology and entomologyArts of investigation and detective
work
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MODULE 4Diagnosing plant problems: Plant Diseases
Plant Problem Diagnosis:Preliminary Considerations
Know Normal Appearance of Plant
Proper plant identification is critical.
Scientific vs. common names
Variety or cultivar
Recognize healthy plant appearance. Whats normal for specific plant?
Compare with healthy plants of same genus,species and cultivar.
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MODULE 4Diagnosing plant problems: Plant Diseases
Plant Problem Diagnosis Steps1. Consider the Possible Agents:
Abiotic non-living agent
Damage from chemicals, weather,mechanical
Nutritional problems
Biotic living agent Pathogens - parasitic microorganisms that
cause diseases
Pests insects or mammals feeding on or
damaging plants
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MODULE 4Diagnosing plant problems: Plant Diseases
Plant Problem Diagnosis Steps2. Consult literature resources for
possible diseases and disorders.
Indexes listing hosts and theirpathogens
Websites providing information
Books with background info and
host/pathogen listsCompendia for information on specific
crops
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MODULE 4Diagnosing plant problems: Plant Diseases
Plant Problem Diagnosis Steps3. Investigate symptom progression.
Biotic disease symptoms progressand nearby plants become infected.
Abiotic disease generally a lack ofsymptom progression. Does not
spread. Exception nutritional symptoms
progress slowly.
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MODULE 4Diagnosing plant problems: Plant Diseases
Plant Problem Diagnosis Steps
4. Ask questions
When was the problem noticed? Was the damage sudden or gradual?
How old are affected plants?
Percentage of plants affected? What is the degree of injury?
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MODULE 4Diagnosing plant problems: Plant Diseases
Plant Problem Diagnosis Steps5. Observe patterns. Determine prevalence of problem
Large area/All plants generallyabiotic
Scattered, localized generally biotic
Check for distribution of symptoms
Uniform generally abiotic
Random generally biotic
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MODULE 4Diagnosing plant problems: Plant Diseases
Observation of Patterns
Scattered symptom
distribution
Random pattern ofdamage
Loblolly pine killed by southernpine beetle
Photo: R. Billings, Texas Forest Service,http://www.forestryimages.org
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MODULE 4Diagnosing plant problems: Plant Diseases
Observation of Patterns
Symptoms distributed
in a large area.Damage pattern isuniform.
Cotton field with chemicaldamage
Used by permission of M. Williamson
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MODULE 4Diagnosing plant problems: Plant Diseases
Plant Problem Diagnosis Steps6. Review cultural practices.
Proper planting technique
Fertilizer and pesticide application Irrigation frequency
7. Review environmental conditions. Temperature extremes
Drought or excess rain
Soil type and conditions
8. Check host specificity many hosts
may mean an abiotic problem
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MODULE 4Diagnosing plant problems: Plant Diseases
Plant Problem Diagnosis Steps
9. Check for symptoms and signs.
Symptoms - plant reactions oralterations of a plants appearancedue to a disease or disorder
Signs - actual pathogen, parts or by-
products seen on a diseased hostplant
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MODULE 4Diagnosing plant problems: Plant Diseases
Symptoms Identify and classify symptoms
Underdevelopment
Overdevelopment Necrosis or death
Alteration of normal appearance
Wilting
Identify plant parts affected
May need to identify source of symptomswithin plant system
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MODULE 4Diagnosing plant problems: Plant Diseases
SymptomsUnderdevelopment Stunting of plants,
leaves Shortened
internodes
Inadequatechlorophyllproduction
Caused by manytypes of pathogens
Photo: J. Dunez, www.forestryimages.org
Chrysanthemum stunt viroid infection ofchrysanthemum showing stunting andearlier blooming of affected plants; healthy
plants in middle.
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MODULE 4Diagnosing plant problems: Plant Diseases
Symptoms -
Overdevelopment
Galls form on all plantparts, caused by
many pathogens.
Oak leaf blister, caused by Taphrinacaerulescens.
Gall on stem of eastern redcedar
caused by Agrobacteriumtumefaciens.
Overgrowth of leaf tissuecauses thickening and
distortion.
Photo: Edward L. Barnard, FloridaDepartment of Agriculture and ConsumerServices, www.ipmimages.org
Photo: Joseph O'Brien, USDA Forest Service,www.ipmimages.org
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MODULE 4Diagnosing plant problems: Plant Diseases
SymptomsOver-development - more biotic causes Root knot nematodes - root galls Callus formation around cankers
Tissue proliferation -some downy mildewsand phytoplasmas
Some insects and mites also cause galls.
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MODULE 4Diagnosing plant problems: Plant Diseases
SymptomsOver-development
Abiotic causes
Oedema
Fasciation can bephysiological or due
to biotic causes.
Some tree burlsOedema of camellia, a physiologicaldisorder
Used by permission of M. Willliamson
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MODULE 4Diagnosing plant problems: Plant Diseases
Symptoms and SignsTissue Necrosis
Fungal leaf spots
Usually round, not vein-limited
Elongated on narrowleaves or stems
May have alternatingzones of light and darktissue
Sporulation or myceliamay be evident
Target spot of tobacco, caused byThanatephorus cucumeris.
Photo: Paul Bertrand, University of Georgia,www.ipmimages.org
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MODULE 4Diagnosing plant problems: Plant Diseases
Symptoms and SignsTissue Necrosis
Bacterial leaf spots
Often dark and water-soaked
Often vein-limited,giving angular shape
Bacterial flowobserved undermicroscope
Bacterial leaf spot of sweet peppercaused by Xanthomonas campestrispv. vesicatoria
Photo: Volcani Center Archives, AgriculturalResearch Organization, www.ipmimages.org
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MODULE 4Diagnosing plant problems: Plant Diseases
Symptoms and SignsTissue Necrosis
Fruit rots
Firm or soft andwatery
Colors vary
Fungal sporulationmay be present
Fungal and bacterialcausesBrown rot of peach, caused by
Monilinia fruticola
Photo: Clemson University - USDA CooperativeExtension Slide Series, , www.ipmimages.org
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MODULE 4Diagnosing plant problems: Plant Diseases
SymptomsTissue Necrosis
Cankers = localized
necrotic lesions Sunken or swollen or
both
Mainly caused byfungi and bacteria
Mechanical injurycan causeSugar maple canker caused by
Nectriaspp.
Photo: Joseph O'Brien, USDA Forest Service,www.ipmimages.org
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MODULE 4Diagnosing plant problems: Plant Diseases
SymptomsTissue Necrosis
Blight = rapid death
or dieback. Also from coalescing
leaf spots, e.g. earlyblight of tomato
Mainly fungal andbacterial causes
Fire blight caused by Erwinia amylovora
Photo: Robert L. Anderson, USDA Forest Service,www.ipmimages.org
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MODULE 4Diagnosing plant problems: Plant Diseases
SymptomsTissue Necrosis
Dieback - many causes
Girdling cankers. Followdieback to detect
Dieback pathogens w/outcankers
Root problems
Mechanical, chemical orcold damage
Pitch canker of Virginia pine, causedby Fusarium subglutinans
Photo: Edward L. Barnard, Florida Department ofAgriculture and Consumer Services, www.ipmimages.org
O i i i
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MODULE 4Diagnosing plant problems: Plant Diseases
SymptomsTissue Necrosis
Root rots
Root lesions Darkening and
softening of roots
Sloughing off of outer
tissues Yellowing of foliage
and stunting of plants
Fungal and bacterial
causes
Root rot of boxwood, caused byPythiumsp.
Used by permission of M. Williamson
MODULE 4 Di i l bl Pl Di
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MODULE 4Diagnosing plant problems: Plant Diseases
SymptomsTissue Necrosis
Damping off
Rapid death ofseedlings and cuttings
Stem infected at soilline, seedling topples
Spreads rapidly undercrowded conditions
Mainly fungal agentsDamping off of tobacco, caused byRhizoctoniaspp. and Pythiumspp.
Photo: Clemson University - USDA Cooperative ExtensionSlide Series, www.ipmimages.org
MODULE 4 Di i l t bl Pl t Di
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MODULE 4Diagnosing plant problems: Plant Diseases
SymptomsWilting
Biotic factors
Root, crown or stem rots
Vascular wilts
Root crown or stemdamage from insects oranimals
Mainly fungal andbacterial causes
Used by permission of M.Williamson
Stem wilt of Exacumfrom INSVinfection
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MODULE 4Diagnosing plant problems: Plant Diseases
Symptoms
Wilting
Abiotic factors
Damage fromweather extremes
Dry or flooded soil
Mechanical damageto roots, crown orstemCold damage on azalea
stem. Shoots wilt above
damage.
Used by permission of M. Williamson
MODULE 4 Di i l t bl Pl t Di
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MODULE 4Diagnosing plant problems: Plant Diseases
SymptomsAlteration of normal
appearance
Mosaic Irregular patches of
discolored tissue.
Often with distortion
Viruses mainly
Mosaic symptoms on cucumber due toa viral infection
Photo: David B. Langston, University of Georgia,www.ipmimages.org
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MODULE 4Diagnosing plant problems: Plant Diseases
SymptomsAlteration of normal
appearance
Ringspot On leaves and fruits.
Distinct ring shapedlesions, often in
concentric zones
VirusesTomato spotted wilt virus (TSWV) ongeranium leaf
Photo: Dr. Backhaus, Biologische Bundesanstalt frLand- und Forstwirtschaft, www.ipmimages.org
MODULE 4 Di i l t bl Pl t Di
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MODULE 4Diagnosing plant problems: Plant Diseases
SymptomsAlteration of normal
appearance
Abiotic causes
Chemical damage
Nutritional deficiencies
Cotton damage by the herbicide 2,4-D
Used by permission of M. Williamson
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MODULE 4Diagnosing plant problems: Plant Diseases
Symptoms
Alteration of normalappearance
Yellowing
Often nutritional,cultural orenvironmental
Root malfunctionbiotic or abiotic
Nematode infestation Yellows phytoplasma
diseasesBurford hollies yellowing dueto root malfunction. Soil ispoorly drained.
Used by permission of M. Williamson
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MODULE 4Diagnosing plant problems: Plant Diseases
SymptomsBe aware of symptom variability.
May have more than one problem.
More than one pathogen may be involved.
Pathogens have varying levels of virulence.
Environmental conditions can affect symptom
expression.
Host genetics and physiology can effect symptomexpression.
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MODULE 4Diagnosing plant problems: Plant Diseases
Symptom variability
due to multiple pathogens Peach seedling on left
infected with both
Prune dwarf virus(PDV) and Prunusnecrotic ringspot virus(PNRSV)
Seedling in middleinfected with PDValone
Seedling on rightinfected with PNRSV
alone
Peach seedlings infectedby single or multiple
viruses show symptomvariability.
Used by permission of S. Scott
MODULE 4 Diagnosing plant problems: Plant Diseases
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MODULE 4Diagnosing plant problems: Plant Diseases
Signs
Fungal signs
Evidence of
pathogen on tissue. Spores, mycelia or
fruiting bodies.
Use hand lens or
knife for fielddetection.
White mycelia of Armillariasp. ontree trunk affected by Armillaria
root and stem rot.
Photo: USDA Forest Service Archives, USDAForest Service, www.ipmimages.org
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MODULE 4Diagnosing plant problems: Plant Diseases
Signs
Fungal signs
Fruiting bodies
Shape of fruitingbody aids in fungalidentification.
Tissue location may
help differentiatebetween species.
White rust of chrysanthemum, fruitingbodies of Puccinia horiana
Photo: Central Science Laboratory, HarpendenArchives, British Crown, www.ipmimages.org
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MODULE 4Diagnosing plant problems: Plant Diseases
Signs
Fungal signs
Powdery mildew
fungi form myceliaand spores on tissuesurface.
Powdery material
rubs off. Leaves often
distorted, discolored
Dark, round fruiting
bodies form in fall.
Oidiumsp. causing powderymildew on Viburnum
suspensum.
Used by permission of M. Williamson
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MODULE 4Diagnosing plant problems: Plant Diseases
Symptoms and Signs
Downy mildews oftenproduce angular leafspots.
Downy mildewsdevelop sporulation
on leaf undersidesonly.
Downy mildew of veronica, caused byPeronospora sordida
Used by permission of M. Williamson
Downy mildew of Buddleiacaused by Peronospora harotii.
Used by permission of M. Williamson
Used by permission of M. Williamson
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MODULE 4Diagnosing plant problems: Plant Diseases
Signs
Bacterial signs
Streaming from freshly
cut stem in water.
Stringing from cut
stems pushed together,then pulled apart.
Bacteria flow observed
from tissue mount on
compound microscope.
Bacterial ooze can beobserved on-site withsome diseases.
Bacterial streaming from tomatoinfected by Ralstonia
solanacearum.
Used by permission of M. Williamson
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MODULE 4 Diagnosing plant problems: Plant Diseases
Plant Problem Diagnosis Steps
12. Laboratory Examination and Testing
Dissecting microscope Compound microscope
Electron microscope
Moist chamber incubation
Culturing Additional tests for biotic agents Tests for abiotic agents
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MODULE 4 Diagnosing plant problems: Plant Diseases
Laboratory Examination
Examination using dissectingmicroscope
Observe sporulation
thats invisible tonaked eye.
Closer view of
structures seen bynaked eye
Nematologist can IDnematodes to
genus.
Used by permission of M. Williamson
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MODULE 4 Diagnosing plant problems: Plant Diseases
Laboratory Examination
Examination using microscopeof higher magnification
ID fungi to genus or to
species. View bacterial flow;
observe morphology athighest magnification.
View virus inclusionbodies.
Using electronmicroscope, view
viruses, phytoplasmas
Used by permission of M. Williamson
Rust spores, Pucciniasp.
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MODULE 4 Diagnosing plant problems: Plant Diseases
Laboratory tests
Moist Incubation
Goal to induce
sporulation Important for
obligate fungalpathogens
Avoid overly moistconditions.
Can surface sterilize
Used by permission of M. Williamson
Moist chamber
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MODULE 4 Diagnosing plant problems: Plant Diseases
Laboratory tests
Fungal isolation
Surface sterilize.
Use margin ofdiseased area.
Nutritive agar media,can be selective
Diagnostician canoften ID to genusfrom appearance ofculture
Used by permission of M. Williamson
Fungal culture.
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MODULE 4 Diagnosing plant problems: Plant Diseases
Isolate identification
Fungal identification Other methods
Examination and comparison withdrawings in literature
Utilizing keys in literature
Literature sources for host diseasesand disorders
Serological, molecular, other tests
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g g p p
Laboratory tests
Bacterial isolations
Grind tissue in
sterile water. Streak suspension
on bacterialmedium.
Can use selectivemedia
Transfer single,
isolated colony
CulturesofRalstonia
solanacearum
Used by permission of K. Ong
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g g p p
Isolate identification
Bacterial identification
Biochemical tests
Carbohydrate utilization (BIOLOG) Fatty acid methyl ester analysis
(FAME)
Molecular methods Polymerase chain reaction (PCR)
Serological tests, e.g. ELISA
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g g p p
Identification of other pathogens
Non-culturable pathogens
Viruses, viroids
Phytoplasmas
Fastidious bacteria
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g g p p
Identification of non-culturable
pathogensMethods
Serological tests, e.g. ELISA
Electron microscopy
Staining for virus-induced inclusionbodies
Molecular tests, e.g. PCR
Enzyme activity testing
Host range testing
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g g p p
Identification of other pathogensELISA tests
Multi-well test formultiple samples
Individual ELISA kit
Usedby permission of M. Williamson
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g g p p
Identification of Nematodes
Extraction from Soil and Plant Material
Soil extraction using centrifugal flotation
Baerman funnel techniques for soil andtissue
Mist chamber extraction for nematodes inroot or stem tissue
Direct examination of nematodes intissue.
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Laboratory tests
Diagnostic tests for abiotic causesSoil, water
pH testingNutrient analysis
Soluble salts analysis
Analysis for chemicals
Plant tissue tests
Nutrient analysis
Analysis for chemicals
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Plant Disease Diagnosis Steps
13) Investigate pathogenicity.
Is identified organism a known pathogen
- of host?
- of hosts in same genus?
Consult literature to determine
If not a host, Kochs Postulates may be next step A lengthy process, rarely used in routine
diagnoses
Problem arises when organism cannot be
cultured
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Kochs Postulates
Robert Koch German physician in late1800s
Proved that a bacterium caused anthraxin cattle
Developed steps proving the bacterium
was causal
Same steps used to prove pathogenicityfor plant disease organisms
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Kochs Postulates
1. Note constant association oforganism with diseased plants and
consistent, observable symptoms.2. Isolate and characterize organism in
pure culture.
3. Inoculate healthy plant with organism,and observe the same disease andsymptoms.
4. Re-isolate same organism.
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Plant Disease Diagnosis Steps
14. Final Diagnosis
All information compiled and analyzed
Organism identified, found to be pathogen ofhost
OR
Lab tests, other information reveal an abioticcause
15. Develop control recommendations andpresent to grower.
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Meg Williamson, Clemson University
Melissa Riley, Clemson University
Otis Maloy, Washington State University
Authors
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This publication can be used for non-profit, educationaluse only purposes. Photographers retain copyright tophotographs or other images contained in this publicationas cited. This material was developed as a core trainingmodule for NPDN First Detector Training. The authors
and website should be properly cited. Images orphotographs should also be properly cited and credited tothe original source.
Publication Number: 0013 Publication Date: December 2006