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Garden CSI: Part II. Jim Jacobi. Extension Plant Pathologist Alabama Cooperative Ext. System. Plant Problem Diagnosis A process of elimination. Identify the type of plant Start with a list of possibilities based on plant species and time of year

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garden csi part ii

Garden CSI:Part II

Jim Jacobi.

Extension Plant Pathologist

Alabama Cooperative Ext. System

plant problem diagnosis a process of elimination
Plant Problem DiagnosisA process of elimination
  • Identify the type of plant
  • Start with a list of possibilities based on plant species and time of year
      • Red Maple – Phyllosticta leaf spot, gloomy scale
      • Flowering Dogwood – Powdery mildew, spot anthracnose, dogwood borer
  • Look for clues and patterns (symptoms and signs)
  • Rule out biotic and abioticproblems, narrow the list of possibilities
  • Repeat steps 3 and 4, if needed
  • Consult expert or send sample to a diagnostic lab



T. Stebbins. Univ. of TN

  • Identify and classify symptoms
    • Underdevelopment of plant tissues - stunting
    • Overdevelopment of plant tissues - galls
    • Necrosis or death – leaf spots, dieback
  • Identify plant parts affected
signs and symptoms
Signs and Symptoms

Types of arthropod feeding damage

  • Stippling
  • Chlorosis
  • Sooty Mold
  • Leafmining
  • Leaf Defoliaters
  • Spider Mites
  • Borers
  • Root Damage
  • Learn to recognize the different types of feeding damage



Lacy L. Hyche, Auburn University,

signs and symptoms8
Signs and Symptoms
  • Look for signs of insect frass or insect fecal material
  • Can be an early warning sign of defoliators and other types on insects
  • Look for frass dropping on sidewalks, leaves, bark and around the base of trees.

Lesser canna leafroller larvae and frass

signs and symptoms9
Signs and Symptoms

Frass tubes from granulate ambrosia beetle

signs and symptoms10
Signs and Symptoms

Over-development of tissues

  • Some insect and mite species can induce gall formation on a variety of host plant structures.
  • Gall-makers are generally host plant specific.

Eyespot Gall

A mite gall,

Aculops laevigata on willow

Photo: William M. Ciesla, Forest Health Management International,

Gall Mite Damage

Photo: Petr Kapitola, Forestry and Game Management Research Institute - Czechia,

signs and symptoms11
Signs and Symptoms

Over-development of tissues

  • How do you know if an insect has caused this damage?
  • Closely examine plant deformation.
  • Cut open gall.
  • Exit holes, frass, empty larval chambers, etc.
  • Rear insects to adult stage.

cynipid gall wasps

Photo: Ronald F. Billings, Texas Forest Service,

oriental chestnut gall wasp

Photo: Jerry A. Payne, USDA Agricultural Research Service,

signs and symptoms12
Signs and Symptoms

Over-development of tissues

  • Bacterial and fungal galls may resemble insect galls.
  • Crown gall bacterium causes galls on roots, crowns and stems.
  • Fungi can also form large galls that superficially resemble crown gall

Crown gall on eastern red cedar

Photo: Edward L. Barnard, Florida Department of Agriculture and Consumer Services,

signs and symptoms13
Signs and Symptoms

Over-development of tissues

  • Phomopsis gall on oak
  • In this case, there are no exit holes, frass, empty larval chambers, etc.
signs and symptoms14
Signs and Symptoms

Tissue Necrosis

  • Fungal leaf spots
  • Usually round, not vein-limited
  • Elongated on narrow leaves or stems
  • May have alternating zones of light and dark tissue
  • Sporulation, mycelia, or small dot-like fruiting bodies may be evident

Leaf spot of Indian hawthorn. R. K. Jones

signs and symptoms15
Signs and Symptoms

Fungal fruiting bodies

Leaf spot on red maple cause by the fungus


signs and symptoms16
Signs and Symptoms

Tissue Necrosis

Bacterial leaf spots

  • Often dark and water-soaked
  • Often vein-limited, giving angular shape
  • Bacterial “ooze” or ‘flow’ observed under microscope

Bacterial leaf spot of hibiscus. A. R. Chase



example english ivy
Example - English Ivy
  • Both bacterial and fungal leaf spots occur on English ivy.
  • Use signs and symptoms to determine the cause of the spots

R. K. Jones/NCSU

example english ivy18
Example - English Ivy
  • Fungal Leaf Spot (Anthracnose)
  • Large, irregularly shaped, tan to brown spots
  • Have numerous, tiny, dark-brown dots (fruiting bodies) on lower surface of leaf

Moorman PSU

Moorman PSU

example english ivy19
Example - English Ivy
  • Bacterial Leaf Spot
  • Circular, dark-brown to black spots, often with yellow halo
  • Viewed on underside of leaf spots may appear greasy
  • No fruiting structures in spots

Moorman Penn State Univ.

A. S. Windham – Univ. Tenn.

signs and symptoms20
Signs and Symptoms

Necrosis of tissue


  • Several possible cause for damage
  • Feeding damage from several types of insects can lead to limb dieback.
  • Bacterial and Fungal Cankers
  • Root problems
  • Death of the host may result.

Botryosphaeria dieback on rhododendron

M. Daughtrey/APS Press

signs and symptoms21
Signs and Symptoms

Azalea lace bug damage

Types of Insect Feeding Damage

 Insects with piercing- sucking mouthparts cause stippling and/or chlorosis on the host.

 Example groups: aphids, true bugs, hoppers, scale insects, whiteflies, etc.

Lacebug Damage on Azalea

signs and symptoms22
Signs and Symptoms

Types of Insect Feeding Damage

  • Presence of Sooty Mold may suggest an infestation of honeydew producing insects such as scales, mealybugs, whiteflies, or aphids.
  • Presence of ants may also be an indicator of these insects!
  • Look up. Insect problem maybe in nearby trees. Asian Woolly Hackberry Aphid

Sooty mold on crape myrtle

signs and symptoms23
Signs and Symptoms

oak skeletonizer

Types of Insect Feeding Damage

Leaf Defoliaters

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

Top Photo: James Solomon, USDA Forest Service,

maple trumpet skeletonizer

Bottom Photo: E. Bradford Walker, Vermont Department of Forests, Parks and Recreation,

signs and symptoms24
Signs and Symptoms

columbine leafminer

Types of Insect Feeding Damage


  • Insects that produce characteristic “mines” in leaves by feeding.
  • Formed by various insects including flies, wasps, moths, and beetles.
  • Some may be confused with leaf spot diseases

Top Photo: Lisa Ames, UGA,

Solitary oak leafminer

James Solomon, USDA Forest Service,

Aspen blotchminer

signs and symptoms25
Signs and Symptoms

Types of Arthropod Feeding Damage

Spider Mites

  • Leaf damage includes flecking, bronzing, and/or scorching of leaves.
  • Use hand-lens to see mites
  • Tap leaves on white paper
  • Several natural enemies. Most problematic in heavy insecticide use areas.

Spider mite damage on hydrangea

Photo: Mississippi State University Archives, Mississippi State University,

twospotted spider mite

signs and symptoms26
Signs and Symptoms


  • Don’t forget to look for potential insect and disease damage on roots!

Aspen root girdler

Top Photo: Ostry, Mike. USDA Forest Service.

Scarab beetle larval feeding damage on root system of pine

Bottom Photo: Robert L. Anderson, USDA Forest Service,

case 1 leaf spots on butterfly bush buddleia x weyeriana28
Case #1 – Leaf spots on Butterfly Bush (Buddleia x weyeriana)
  • Fungal sporulation on underside of leaf opposite chlorotic spots
  • Downy mildew

Downy Mildew

S. Jeffers/Clemson

southern purple mint moth on rosemary
Southern Purple Mint Moth on Rosemary

Southern purple mint moth larva

Southern purple mint moth adult


Case #3 – Leaf spots on Brunnera ‘Jack Frost’

  • No fungal fruiting bodies or sporulation
  • No bacterial streaming or ‘ooze’
  • Foliar nematode emerging from leaf tissue on microscope slide

T. Stebbins. Univ. of TN

case 4 wilt of oakleaf hydrangea35
Case #4 – Wilt of Oakleaf Hydrangea
  • Adequate soil moisture
  • Presence of white fungal mycelium under bark
  • Armillaria root rot
case 5 tip dieback of southern magnolia37
Case # 5 – Tip Dieback of Southern Magnolia
  • Branch dieback of pencil sized branch tips
  • Small entrance holes (< 1mm) on bottom side of the limbs
  • Black twig borer (Xylosandrus compactus) within stems

Some of the slides were adapted from NPDN slidesets developed by the following authors

  • Amanda C. Hodges, University of Florida
  • Amanda M. Ellis, University of Florida
  • Meg Williamson, Clemson University
  • Melissa Riley, Clemson University
  • Otis Maloy, Washington State University