1 Plant Disease and Diagnosis Dr. Tamla Blunt Plant Pathologist Colorado State University Why Do We Need to Know Plant Pathology? • A lot of the questions at the Help Desk are about plant problems • Plant Pathology give you a background in types of plant problems • Terminology/definitions/descriptions are important in Plant Pathology (kind of like a foreign language) • We use terms like ‘generally’, ‘usually’, ‘consistent with’, ‘sometimes’, ‘it depends’ • A background in PP can help you with the diagnostic process; determine what questions to ask your clients Plant Problem Diagnosis Diagnosis –process used for the identification of problems; consider it ‘CSI’ for plants Tools: • Plant sciences, especially plant pathology and entomology • Art of investigation and detective work Some Other Tools • Items that are handy to have in a sample collection/plant diagnostic toolbox: • Hand lens/ magnifying glass/binoculars; • Pocket knife; • Soil probe; • Shovel; • Small notebook w/pencil; • Plastic baggies; • Small saw/hand pruners What is a Plant Disease? Abnormal growth/ dysfunction of a plant Environment Causal Agent Host Plant Disease Pyramid/Triangle 1 2 3 4 5 6
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Plant Disease and Diagnosis
Dr. Tamla Blunt
Plant Pathologist
Colorado State University
Why Do We Need to Know Plant Pathology?• A lot of the questions at the Help Desk are about
plant problems• Plant Pathology give you a background in types of
plant problems• Terminology/definitions/descriptions are important
in Plant Pathology (kind of like a foreign language)• We use terms like ‘generally’, ‘usually’, ‘consistent
with’, ‘sometimes’, ‘it depends’• A background in PP can help you with the
diagnostic process; determine what questions to ask your clients
Plant Problem Diagnosis
Diagnosis –process used for the identification of problems; consider it ‘CSI’
for plants
Tools:• Plant sciences, especially plant pathology and
entomology• Art of investigation and detective work
Some Other Tools• Items that are handy to
have in a sample collection/plant diagnostic toolbox:• Hand lens/ magnifying
glass/binoculars;• Pocket knife;• Soil probe;• Shovel;• Small notebook
w/pencil;• Plastic baggies;• Small saw/hand pruners
What is a Plant Disease?Abnormal growth/ dysfunction of a plant
Environment Causal Agent
Host
Plant Disease Pyramid/Triangle
1 2
3 4
5 6
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Plant Problem Diagnosis Steps• Know the normal appearance of the plant
• Symptoms and Signs
• Abiotic vs. Biotic• Review environmental conditions
• Malformation to less severely damaged plant parts
• Late spring & early fall are most common times for low temp plant (flower/foliage) injury• Water freezes and disrupts cell membranes• Symptoms may resemble foliage/shoot diseases caused by
pathogens
Moisture
• Low soil moisture effects• Plants grow poorly• Plants are unproductive• Stunted appearance• Usually pale green to light
yellow• Can wilt and die• Scorched leaves• Dieback
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Moisture
• Scorch: Leaves turn brown from outer edges inward; generally evenly distributed around the leaf margin
Moisture
• Winter desiccation common on conifers• Needle scorching• Twig dieback
• Frozen soils don’t allow for water uptake which is needed because of transpiration during winter
Moisture
• Winter desiccation: needles brown from tips inward
Drought Injury Examples
How Does Drought Happen?
• Water lost faster than replacement
• May not have sufficient water for roots
• Water available, BUT roots not functioning/soil frozen
• Stem/trunk damage
Additional Facts:
• New growth usually masks damage
• Large percentagemust be damaged before plant health endangered
• Feel buds to check health
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Additional Facts:
• Disease organism erupts through needles
Hyg.ipm.illinois.edu
Cold damage starts at tips of needles and moves down; no organisms erupt through needles
Drought Management
• Identify possible causes/correct
• Fall and winter water: apply water monthly to absorbing roots from Nov 1 - March 1
• Fall water most critical
• Roots still functioning until soil temp drops below 40 degrees
• Abiotic = non-living causes such as the environment
Biotic Causes of Disease
• Living organisms that cause plant problems• Fungi• Bacteria • Virus• Phytoplasma• Nematodes• Parasitic Plants• Animals (not covered here)• Insects (a different
presentation)
Fungi and Bacteria Are Spread by:
• Wind
• Water (rain, irrigation)
• Soil
• Animals (including us)
• Equipment
• Plant Material
• Insects
Fungi and Bacteria Infect by:
• Entering the plant through natural openings• Stomates• Lenticils
• Entering through wounds
• Producing enzymes that break down cuticle
Lenticels
Sooty bark canker
Wound
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Fungi and Bacteria Cause:
• Leaf spots and curling
• Galls
• Soft rots
• Wilts
• Cankers
• Stem and root rots
Fungi Characteristics:
• Variety of sizes
• No chlorophyll
• Most harmless to plant health (saprophytes)
• Most reproduce by spores
Margins?•Marginal areas often exist between dead and healthy tissue in fungal infections
Distinct margins usually point to fungal problem and will often have a halo around the margin
But Beware of Exceptions…
Some fungal diseases have feathery margins!
Black spot rose
Apple scab
Fungal ID Tips
• Dry, fluffy (fuzzy)
• Distinct borders
• Damage is random
Powdery Mildew • Gray or white web-like covering
• Looks like flour or talcum powder spill
• Host specific
• Requires humidity but not free moisture
• Very common on plants in Colorado
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Plant Damage from P.M.
• Aesthetic damage – discoloration• Reddening?
• Distortion
• Premature leaf drop
• Chronic stress
Powdery Mildew Management
Plant
Organism Environment
Fungicides, sulfur
Water
Potassium or sodium bicarbonate
Neem or horticultural oil
Time
Use Caution! Cultural Management
• Site correctly (avoid dead air pockets)
• Space for good air circulation• Prune/thin appropriately for
plant• Avoid over fertilization• Avoid overwatering• Keep water out of plant • Water early in day• Remove infected material• Rake up fallen leaves …why?
Marssonina Leaf Spot
• Characteristics:• Spots are necrotic,
various sizes • May cause premature
leaf drop• May lead to chronic
stress
Marssonina Leaf Spot
• Infection occurs at budbreak
• Problem appears mid summer
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Marssonina Leaf Spot Management
Plant
Organism Environment
No resistant cultivars
Fungicide: Daconil(protectant - at bud break)
Rake up leaves
Proper spacing, thinning, pruning
Keep water out of canopy
Time
To Compost or Not to Compost, That is the Question…
• Must be “hot” compost ( at least140 degrees, consistent throughout the pile)
• Overall health clue• Sometimes easier to determine on conifers
Plant Problem Diagnosis Steps
• Know the normal appearance of the plant
• Symptoms and Signs
• Abiotic vs. biotic• Review environmental conditions
• How do symptoms/signs progress?
• Review cultural practices
• Observe patterns
• Ask questions
• Consult literature/control measures/final diagnosis• Use site:edu after search term when looking on the internet
Ask Questions
• Consider:• Many folks don’t offer
(know!) all the information• About 6 major symptoms for
hundreds of causes• Cause may be what
homeowner is doing/not
Ask More Questions! (More clues)
• Age of plant? • Exposure of plant?• When first noticed?• Has it happened before?• How has the plant been cared for?• Any other plants damaged?• What time of year is it?• Weather concerns?
Examine Smaller Branches
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Look at Leaves Look at Flowers
Ask for Photographs
Lower trunk
Upper trunk
Analyze information
• Research/read/references
• Is a lab test needed?
• Do you need more info?
• Analyze information
Analyze information
• Start with biotic
• Move to abiotic
• Consider primary vs. secondary (contributing) factors
Primary vs. Secondary Factor
• What is really causing the problem? (1)
• What is contributing to the problem? (2)
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Significance of Findings
• Is IT a problem or normal?
• Is IT affecting plant health (or will it)?
• Is IT affecting aesthetics?
• What does the client want?
• What can reasonably be done?
• Provide the client with all research based information-let them decide the course of action
“The first surefire rule of plant diagnostics is nothing is surefire” - Boggs, Draper, Chatfield, Ellis, Boehm, the OSU Extension