diagnosing plant problems
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Diagnosing Plant Problems
The Art and Science of Diagnosing
Plant Problems
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• 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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• http://coloradoipmcenter.agsci.colostate.
edu
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Plant Problem Diagnosis
Diagnosis –process used for the
identification of problems; consider it
‘CSI’ for plantsTools:
– Plant sciences, especially plant pathology
and entomology – Arts of investigation and detective work
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Field Sample Collection for Diagnosis
• Items that are handyin your toolbox:
– Hand lens/ magnifyingglass;
–
Pocket knife; – Soil probe;
– Shovel;
– Small notebook
w/pencil; – Plastic baggies;
– Small saw/handpruners
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Plant Problem Diagnosis:
Preliminary Considerations
Know Normal Appearance
of Plant
–
Plant identification.• Scientific vs. common
names
• Variety or cultivar
– Recognize healthy plant
appearance.
• What’s normal?
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Plant Problem Diagnosis Steps
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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Plant Problem Diagnostic Steps
Review cultural
practices:•
Proper plantingtechnique
• Fertilizer and pesticide
application
• Irrigation frequency
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Plant Problem Diagnosis Steps
Review environmental
conditions:•
Temperature extremes• Drought or excess rain
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Plant Problem Diagnosis Steps
Ask questions (for example):
• 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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Plant Problem Diagnosis Steps
Observe patterns:
– Determine prevalence
of problem
Large area/All plants
– generally abiotic
– Scattered, localized –
generally biotic – Check for distribution of
symptoms
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Observation of Patterns
Hot spots or pockets
biotic or abiotic
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Observation of Patterns
Symptoms distributed in a
large area.Damage pattern is
uniform.
Winged Euonymus damaged
by excessive soil moisture
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What part of the plant is damaged?
• Leaves, stems, roots,
fruit etc.
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Check for Symptoms and Signs
Symptoms
• Plant reactions or alterations of a plant’s
appearance due to a disease or disorder
Signs
• actual pathogen, parts or by-products seen on
a diseased host plant
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Symptoms
Identify and classify symptoms:
• Underdevelopment
• Overdevelopment
•Necrosis or death
• Alteration of normal appearance
• Wilting
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Symptoms
Underdevelopment
• Stunting of plants,
leaves• Shortened internodes
• Inadequate
chlorophyll production• Caused by many types
of pathogens
Root knot nematodes cause
stunting of tomato plants
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Symptoms
Overdevelopment
• Overgrowth of leaf
tissue causesthickening and
distortion
– Example: Leaf curls
caused by the fungusTaphrina
Peach leaf curl
Chokecherry leaf curl
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Symptoms
Overdevelopment• Galls form on all plant
parts, caused by manypathogens.
• Swelling
Crown gall
Root knot nematode
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Symptoms
Overdevelopment
• Witches broom
• Fasciation
Juniper broom rust
Bacterial fasciation of
geranium
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Symptoms
Overdevelopment
• Blisters
– Oedema or edema is
caused by water
accumulation in tissue
resulting from high
relative humidity andhigh soil moisture
Oedema of camellia, a
physiological disorder
Used by permission of M. Willliamson
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Symptoms and Signs
Tissue Necrosis
• Fungal leaf spots
• Usually round, notvein-limited
• Sporulation or
mycelium may beevident
Anthracnose diseases of cucurbits
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Symptoms and Signs
Tissue Necrosis
• Bacterial leaf spots
– Often water-soaked or
transluscent
– Often vein-limited,
giving angular shape
– Bacterial “flow”
observed under
microscopeBacterial leaf spot of Pumpkin and
squash
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Symptoms and Signs
Tissue Necrosis
• Fruit rots
–Firm or soft andwatery
– Colors vary
– Fungal spores may be
present – Fungal and bacterial
causes Brown rot of peach, caused by
Monilinia fruticolaPhoto: Clemson University - USDA Cooperative Extension
Slide Series, , www.ipmimages.org
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Symptoms
Tissue Necrosis
• Cankers = localized
necrotic lesions – Sunken or swollen or
both
– Mainly caused by fungi
and bacteria
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Symptoms
Tissue Necrosis
• Blight = rapid death or
dieback.
Photo: Robert L. Anderson, USDA Forest Service, www.ipmimages.org
Fire blight caused by Erwinia amylovora
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Symptoms
Tissue Necrosis
• Dieback - many causes
– Girdling cankers. Follow
dieback to detect
– Dieback pathogens w/out
cankers
– Root problems
–
Mechanical, chemical orcold damage
Pitch canker of Virginia pine, caused by
Fusarium subglutinansPhoto: Edward L. Barnard, Florida Department of Agriculture and
Consumer Services, www.ipmimages.org
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Symptoms
Tissue Necrosis
• Root Rots
– Root lesions
– Darkening and softening of
roots
– Sloughing off of outer root
tissue
–
Yellowing of foliage andstunting of plants
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Symptoms
Tissue Necrosis
• Damping off
–Rapid death ofseedlings and cuttings
– Stem infected at soil
line, seedling topples
–Spreads rapidly undercrowded conditions
– Mainly fungal agentsDamping off of tobacco, caused by
Rhizoctonia spp. and Pythium spp.
Photo: Clemson University - USDA Cooperative Extension SlideSeries, www.ipmimages.org
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Symptoms
Wilting
• Biotic Factors –
Root, crown, stem rots• Mainly fungal and bacterial
causes
– Vascular wilt pathogens
• Mainly fungal and bacterial
causes
– Root, crown, or stem
damage from insects or
animals
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Symptoms
Abnormal Color or
Appearance
–
Mottling – Mosaic
– Crinkling
– Stunting
– Vein clearing – Flower break
– Ringspots
T. Lundsgaard, Dept Biology,
KVL, Denmark
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Symptoms
Alteration of normal
appearance distortion
• Abiotic causes• Chemical damage
• Nutritional deficiencies
Used by permission of M. Williamson
Cotton damage by the herbicide 2,4-D
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Changes in ColorYellowing (Chlorosis)
• Generalized degeneration
or disorganization of
chloroplasts• Multiple causes (abiotic,
infectious agents)
• Yellowing symptoms are
often not diagnostic butcan be used in
conjunction with other
symptoms
Symptoms
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Reddening
• Phosphorus deficiency
• Cold temperatures
• Viruses andPhytoplasmas
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Symptoms
– Be aware of symptom variability.
– May have more than one problem.
– More than one pathogen may be involved.
– Environmental conditions can affect symptom
expression.
– Host genetics and physiology can effect symptom
expression. – Primary vs. secondary symptoms
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SignsFungal signs
– Evidence of pathogen
on tissue.
– Spores, mycelium or
fruiting bodies
White mycelium of Armillaria sp. on
tree trunk affected by Armillaria root
and stem rot.Photo: USDA Forest Service Archives, USDA Forest Service,
www.ipmimages.org
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Signs
Fungal signs
– Powdery mildew fungiform mycelia and
spores on tissuesurface.
– Powdery material rubsoff.
–
Leaves often distorted,discolored
Dark, round fruitingbodies form in fall
Oidium sp. causing powdery
mildew on Viburnum suspensum.Used by permission of M. Williamson
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Signs
Bacterial signs
– “Streaming” from freshly
cut stem in water.
– “Stringing” from cut stemspushed together, then
pulled apart.
– Bacteria “flow” observed
from tissue mount on
compound microscope. – Bacterial ooze can be
observed on-site with some
diseases
Bacterial streaming from tomatoinfected by Ralstonia solanacearum.Used by permission of M. Williamson
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Plant Problem Diagnosis Steps
• Consult literature resources for
possible diseases and disorders:
– Host and pathogen indexes
–Websites providing information (be careful withyour sources)
– Books with background info and host/pathogen
lists
–Compendia for information on specific crops
– CSU fact sheets
– Other Land Grant University publications
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Final Diagnosis
• Indicate confidence of diagnosis
– Certain, probable, etc.
• Provide a management strategy (This is what your
client really wants!)• Provide options – let the client make the final
decision
– Can the problem be managed by cultural practices alone?
– Are chemicals necessary?
• Organic vs Synthetic?