Diagnosing Tree Disorders in the Landscape

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Diagnosing Tree Disorders in the Landscape
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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

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Plant Diseases

• Biotic Factors
• Viruses
• Bacteria
• Fungi
• Nematodes
• Abiotic Factors
• Environmental Problems
• Herbicides
• Nutritional Deficiencies
• Pollutants

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Damage from herbivores

• Animals and Rodents
• Insects
• Mites
• Nematodes

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Insect Damage Identification

• Know Common Pest Arthropod Groups!
• Numerous lepidopteran caterpillars (ex.
  armyworms, cutworms)
• Beetles (Order Coleoptera) numerous
  leaf-feeding 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

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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

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Symptom or sign?
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Diagnosis

• Compare plants with disorder to healthy plants
• Roots, stems, leaves, fruits
• Ask questions!
• History, conditions, variety, soil, etc.
• Hypothesis of cause

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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

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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?

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What are viruses and viroids?

• Very small particles of nucleic acid and protein
  (viruses) or naked nucleic acid (viroids)

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Symptoms of Viruses
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Plum Pox Virus
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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

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What do bacteria look like?

• Cant see with the naked eye unless there are a
  LOT of them
• Culture on artificial media (some are not
  culturable on media)

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Bacterial disease symptoms
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Fire blight

• Erwinia amylovora
• Apple, pear, mountain ash, raspberry, hawthorne,
  contoneaster

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What are fungal diseases?

• Cause the majority of economically significant
  plant diseases
• Caused by fungi organisms with threadlike
  hyphae and reproductive structures (spores)

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Fungal Plant Diseases

• Root Diseases - Soilborne and Residue borne
• Cankers
• Rots
• Wilts
• Foliar Diseases Residue borne, wind-blown and
  rain-splashed spores
• Leaf spots and leaf molds

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Fungal symptoms signs
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Dutch Elm Disease in Montana
Beetle Galleries
Lesser European Elm Bark Beetle
Staining in twig
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Cytospora canker - Spruce
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Verticillium Wilt
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Root Rots and Diseases
Wind-thrown Trees
Phytopthora
Armillaria
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Sudden Oak Death Phytopthora ramorum
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Rhizosphaera needle cast

• Rhizosphaera kalhkoffii
• Rainsplash dispersed
• Symptoms
• Reduced needle retention
• Dead (brown) older needles
• Healthy, new needles do not show signs of
  infection

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Powdery mildew
Obligate Parasite Spores airborne over
long distances
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Nematodes a very small, worm-like animal
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Pine Wilt Nematode
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Piercing Sucking Insects

• Insects with piercing-sucking mouthparts cause
  stippling and/or chlorosis on the host.
• Example groups aphids, true bugs, hoppers,
  scale insects, whiteflies

Aphids
Plant Bugs
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Sooty Mold
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Leaf miners
birch leafminer

• Insects that produce characteristic mines in
  leaves by feeding.
• Formed by various insects including flies, wasps,
  moths, and beetles.

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Leaf Defoliaters

• Damage caused to a plant by insect feeding.
• Skeletonizing results when the veins or the
  skeleton of the leaf is left behind.

Grasshoppers
Japanese Beetles
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Spider Mite Damage

• Leaf damage includes flecking, bronzing,
  and/or scorching of leaves.
• Several natural enemies. Most problematic
  in heavy insecticide use areas.

twospotted spider mite
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Damage by Boring Insects

• Insects that bore into a stem, or seedhead
• Damage often results in weakening or killing the
  host

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Emerald Ash BorerWhat 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

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Emerald Ash BorerWhat 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

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Cottony Ash Psyllid
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Woodpeckers and Sapsuckers
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Porcupines
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Deer and Elk Rubs
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Drought Damage

• Trees will shed leaves and needles to prevent
  water loss

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Herbicide?

• History
• Soil analysis or bioassay
• Tissue analysis

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Symptoms of herbicide injury
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Winter Injury
Frost Damage
Desiccation
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Seasonal Needle Cast
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Planting too deep
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Iron Deficiency - Chlorosis
Common in high pH Soils

• Apply sulfur to lower soil pH
• Apply chelated iron fertilizer
• foliar or soil applications

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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!

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Montana State UniversitySchutter Diagnostic Lab

• Physical address
• 121 Plant BioScience Bldg. (PBB)
• Mailing Address
• 119 Plant BioScience Bldg.
• P.O. Box 173150
• Bozeman, MT 59717-3150
• [phone]
• diagnostics_at_montana.edu
• http//diagnostics.montana.edu/