Diagnosing
Tree Disorders
in the
Landscape
What is a plant disease?
Anything that damages plant health
Plant pathology deals with infectious
organisms that reduce plant health,
multiply, and spread: biotic diseases
Plant Diseases
Biotic Factors
–
–
–
–
Viruses
Bacteria
Fungi
Nematodes
Abiotic Factors
– Environmental
Problems
– Herbicides
– Nutritional Deficiencies
– Pollutants
Damage from herbivores
Animals and Rodents
Insects
Mites
Nematodes
Insect Damage Identification
Know Common Pest Arthropod Groups!
Numerous lepidopteran caterpillars (ex.
armyworms, cutworms)
Beetles (Order Coleoptera): numerous leaffeeding and wood-boring pests
Sawflies (Order Hymenoptera)
Various flies (Order Diptera)
Various insects with piercing-sucking
mouthparts including scales, mealybugs,
whiteflies, aphids, psyllids, hoppers, various
other members of the Order Hemiptera.
Spider Mites
Symptoms vs. signs
Symptoms are changes in growth or
appearance of a plant in response to a
damaging factor
Signs are evidence of the damaging factor
Symptom or sign?
Diagnosis
Compare plants with disorder to healthy
plants
– Roots, stems, leaves, fruits
Ask questions!
– History, conditions, variety, soil, etc.
Hypothesis of cause
Diagnosis - Continued
Look for signs of pathogen
–
–
–
–
–
Microscopic examination
Culturing on artificial media
Immunological methods (ELISA, etc)
Nucleic acid methods (PCR, etc)
Electron microscope
Look for signs of insect or animal
–
–
–
–
Organism itself, eggs
Frass
Honeydew
Webbing
What questions do you ask?
History: herbicide application, fungicide
application, insect activity
Pattern: isolated plant, entire field, near
edges, etc? Any spread?
Any variety differences?
Certified planting stock?
What are viruses and viroids?
Very small particles of nucleic acid and
protein (viruses) or naked nucleic acid
(viroids)
icosahedral
tospovirus
rods
flexuous rods
viroid
geminivirus
inclusion body
Symptoms of Viruses
Plum Pox Virus
Bacterial diseases
Bacteria are single-celled, prokaryotic
organism (lack a membrane around the
nucleus of the cell)
Most plant pathogenic bacteria are
gram negative, which means they do
not retain the stain crystal violet when
you do a gram stain
– LPS (lipopolysaccharide) layer around cell
wall
What do bacteria look like?
Can’t see with the naked eye unless
there are a LOT of them
Culture on artificial media (some are not
culturable on media)
Bacterial disease symptoms
Fire blight
Erwinia amylovora
Apple, pear, mountain
ash, raspberry,
hawthorne, contoneaster
What are fungal diseases?
Cause the majority of economically
significant plant diseases
Caused by fungi – organisms with
threadlike hyphae and reproductive
structures (spores)
Fungal Plant Diseases
Root Diseases - Soilborne
and Residue borne
– Cankers
– Rots
– Wilts
Foliar Diseases –
Residue borne, windblown and rain-splashed
spores
– Leaf spots and leaf molds
Fungal symptoms & signs
Dutch Elm Disease in Montana
Beetle Galleries
Lesser European Elm
Bark Beetle
Staining in twig
Cytospora canker - Spruce
Verticillium Wilt
Root Rots and Diseases
Wind-thrown Trees
Phytopthora
Armillaria
Sudden Oak Death
Phytopthora ramorum
Rhizosphaera needle cast
Rhizosphaera kalhkoffii
Rainsplash dispersed
Symptoms:
– Reduced needle retention
– Dead (brown) older needles
– Healthy, new needles do not show signs of
infection
Powdery mildew
Obligate Parasite
Spores airborne over
long distances –
Nematodes: a very small, wormlike animal
Pine Wilt Nematode
Piercing Sucking Insects
Aphids
Plant Bugs
Insects with
piercing-sucking
mouthparts cause
stippling and/or
chlorosis on the host.
Example groups:
aphids, true bugs,
hoppers, scale
insects, whiteflies
Sooty Mold
Leaf miners
birch leafminer
Insects that produce
characteristic
“mines” in leaves by
feeding.
Formed by various
insects including
flies, wasps, moths,
and beetles.
Leaf Defoliaters
Damage caused to a
plant by insect
feeding.
Grasshoppers
“Skeletonizing”
results when the
veins or the
“skeleton” of the
leaf is left behind.
Japanese Beetles
Spider Mite Damage
•
•
twospotted spider mite
Leaf damage
includes flecking,
bronzing, and/or
scorching of leaves.
Several natural
enemies. Most
problematic in heavy
insecticide use areas.
Damage by Boring Insects
Insects that bore
into a stem, or
seedhead
Damage often
results in weakening
or killing the host
Emerald Ash Borer
What does the damage look like?
1. Canopy starts to thin and water sprouts may
start
2. Serpentine feeding just below bark
3. Small, D-shaped exit hole
4. Woodpecker damage another clue to infestation
Emerald Ash Borer
What does it look like?
1. Adult is metallic green, about ½ inch
2. Larvae are flat bodied, about 1 inch
3. Larvae pupate in the tree and adults
emerge from D shaped exit holes
Cottony Ash Psyllid
Woodpeckers and Sapsuckers
Porcupines
Deer and Elk Rubs
Drought Damage
Trees will shed leaves
and needles to
prevent water loss
Herbicide?
History
Soil analysis or bioassay
Tissue analysis
Symptoms of herbicide
injury
Winter Injury
Frost Damage
Desiccation
Seasonal Needle Cast
Planting too deep
Iron Deficiency - Chlorosis
Common in high pH Soils
• Apply sulfur to lower soil pH
• Apply chelated iron fertilizer
foliar or soil applications
How to be a diagnostician
Know the plant involved
– What a healthy plant looks like!
Look for symptoms and signs
Look for patterns
Question the environment
Make a diagnosis, and check the facts!
Montana State University
Schutter Diagnostic Lab
Physical address
121 Plant BioScience Bldg. (PBB)
Mailing Address
119 Plant BioScience Bldg.
P.O. Box 173150
Bozeman, MT 59717-3150
(406) 994-5150
diagnostics@montana.edu
http://diagnostics.montana.edu/