1. Landscape Pests & Diseases:
Diagnosis and Treatment
Leslie Lyles, M.S.
Horticultural Consultant
I.S.A. Certified Arborist (#WE-1220A)

2. Have you ever noticed…
There are more insect and disease
problems in the urban forest than
in natural forests.

3. Urban Forest VS Natural Forests
 Increase stress pre-disposes trees to vigor related
diseases. Since the forest is the normal ecological
niche for trees, it would be expected, in most
cases, that more stress would be found in shade
trees than in forest trees.

4. Don’t Stress Me Out!
When a plant is stressed, it is much more susceptible
to attack by insect and disease organisms. Typically,
95% or greater of the problems seen in the landscape
can be traced back to a cultural (abiotic) cause.

5. Stresses affecting plant health:
 Compacted soil
 Reflective heat
 Sparse or excessive water supply
 Insufficient nutrients
 Chemicals (pesticides, fertilizers)
 Soil Problems (salinity, pH, Boron)
 Air Pollution
 Accidents, vandalism, neglect
 Infestation by pests and disease organisms

6. Urban Forest VS Natural Forests
 Increase stress pre-disposes trees to vigor related
diseases. Since the forest is the normal ecological
niche for trees, it would be expected, in most
cases, that more stress would be found in shade
trees than in forest trees.
 A major responsibility of the diagnostician is to
provide necessary information regarding care to
maintain vigor and to prevent or alleviate as many
adverse stress factors as possible.

7. What can cause Problems?
Abiotic Causes:
Biotic Causes:

8. What can cause Problems?
Abiotic Causes:
 Environmental stress

9. What can cause Problems?
Abiotic Causes:
 Environmental stress
– Flooding or Drought

10. What can cause Problems?
Abiotic Causes:
 Environmental stress
– Flooding or Drought
– Soil problems (Salinity, Boron)

11. What can cause Problems?
Abiotic Causes:
 Environmental stress
– Flooding or Drought
– Soil problems (Salinity, Boron)
– Freeze

12. What can cause Problems?
Abiotic Causes:
 Environmental stress
– Flooding or Drought
– Soil problems (Salinity, Boron)
– Freeze
– Scorch

13. What can cause Problems?
Abiotic Causes:
 Environmental stress
– Flooding or Drought
– Soil problems (Salinity, Boron)
– Freeze
– Scorch
– Air Pollution

14. What can cause Problems?
Abiotic Causes:
 Environmental stress
– Flooding or Drought
– Soil problems (Salinity, Boron)
– Freeze
– Scorch
– Air Pollution
– Reflective Heat

15. What can cause Problems?
Abiotic Causes:
 Environmental stress
 People pressure

16. What can cause Problems?
Abiotic Causes:
 Environmental stress
 People pressure
– Soil compaction and construction damage

17. What can cause Problems?
Abiotic Causes:
 Environmental stress
 People pressure
– Soil compaction and construction damage
– Lawn mower and string trimmer damage

18. What can cause Problems?
Abiotic Causes:
 Environmental stress
 People pressure
– Soil compaction and construction damage
– Lawn mower and string trimmer damage
– Children

19. What can cause Problems?
Abiotic Causes:
 Environmental stress
 People pressure
– Soil compaction and construction damage
– Lawn mower and string trimmer damage
– Children
– Improper handling and planting

20. What can cause Problems?
Abiotic Causes:
 Environmental stress
 People pressure
– Soil compaction and construction damage
– Lawn mower and string trimmer damage
– Children
– Improper handling and planting
– Poor plant selection and placement

21. What can cause Problems?
Abiotic Causes:
 Environmental stress
 People pressure
– Soil compaction and construction damage
– Lawn mower and string trimmer damage
– Children
– Improper handling and planting
– Poor plant selection and placement
– Poor cultural practices

22. What can cause Problems?
Abiotic Causes:
 Environmental stress
 People pressure
Biotic Causes:
 Micro-organisms
 Macro-organisms

23. What can cause Problems?
Biotic Causes:
 Micro-organisms
– Fungi
– Bacteria
– virus

24. What can cause Problems?
Biotic Causes:
 Micro-organisms
– Fungi
– Bacteria
– virus
 Macro-organisms
– Insects
– Animals
– parasitic plants

25. In general:
Non-infectious disorders (abiotic causes)
typically affect the entire plant and more
than just one plant.

26. In general:
Non-infectious disorders (abiotic causes)
typically affect the entire plant and more
than just one plant.
Infectious disorders (biotic causes) typically
affect only a portion of a plant, and not
necessarily every plant of the same species.

27. Plant Diseases
The Disease Process

28. What is disease?
 Abnormal physiology resulting from the
continuous interaction between a host and
a primary causal agent resulting in
characteristic symptoms.

29. Disease Triangle
Environment Pathogen
Ab
s
bu
Diseas e severity
es
un
nd
en
da
a
bl
nc
ra
e
vo
Fa
Duration V irulence
Resistance Disease escape
Host Plant
There must be three factors present for disease development:
susceptible host, pathogen, and a suitable environment. If
any of these factors are absent, there is no disease.

30. Susceptible Host Susceptible Host
Causal Agent
Causal Agent
Environment Environment
Slight Disease Severe Disease

31. Most common pathogens:
 Fungi - powdery mildew, vascular wilts,
Cytospora, Dutch elm disease

32. Most common pathogens:
 Fungi - powdery mildew, vascular wilts,
Cytospora, Dutch elm disease
 Bacteria- Fireblight, some bacterial wilts,
wetwood

33. Most common pathogens:
 Fungi - powdery mildew, vascular wilts,
Cytospora, Dutch elm disease
 Bacteria- Fireblight, some bacterial wilts,
wetwood
 Virus - Rose mosaic virus

34. Treatment of disease:
 Cultural control – Work to prevent the
disease and it’s spread
– Appropriate watering
– Removal of diseased plant tissue
– Select resistant varieties
– Crop rotation

35. Treatment of disease:
 Foliar disease
– Practice good cultural control
– typically, fungicidal sprays are effective

36. Powdery mildew
Powdery mildew

37. Anthracnose
Anthracnose

38. Needle blight
Needle blight

39. Phomopsis
Phomopsis

40. Peach Leaf Curl

41. Rose Mosaic Virus
Rose Mosaic Virus

42. Treatment of disease:
 Foliar disease
 Stem
– typically no good chemical control
– preventative sprays for some i.e., Fireblight
– Practice good cultural control; proper pruning
(proper cut, timing, disinfect tools)

43. Cytospora canker

44. Spruce with Cytospora

46. Fireblight

47. Nectria canker

48. Bacterial Blight

49. Crowngall
Crowngall

50. Bacterial wetwood
Bacterial wetwood

51. Treatment of disease:
 Foliar
 Stem
 Root
– keep trees vigorous
– avoid wounding roots and heavy pruning
– Practice good cultural control (manage
irrigation, prevent soil compaction or root
damage, avoid infected plants)

52. Phytophthora
Phytophthora

54. ithium blight

55. Treatment of disease:
 Foliar
 Stem
 Root
 Vascular
– increase vigor with fertilization and water
– systemic chemicals in very early stages
– cultural control (control insect vectors,
eradicate infected host plants)

56. Verticillium Wilt
Verticillium Wilt

57. Dutch Elm Disease
Dutch Elm Disease

58. Insects

59. Treatment of insect problems:
 Not all insects cause problems! Know what the
insect is and the plant’s/client’s level of tolerance
before treating.

60. Ladybug larvae

61. Ladybug adult & larvae
Adult Larvae
Ladybird beetle

62. Praying Mantis
Lacewing
Ladybird Beetle

63. Beneficial?

64. Earwig
Garden spider
Parasitic wasp
Assassin bug
Beneficial? Yes

67. Treatment of insect problems:
 Not all insects cause problems! Know what the
insect is and the plant’s/client’s level of tolerance
before treating.
 Consider cultural control and least toxic methods
first (hosing plant, soap solutions, oil sprays,
pruning).

68. Spittle Bug

72. Aphids

73. Wooly Apple Aphid

74. Aphid on Pine

75. Scale

76. Scale Insects

77. Treatment of insect problems:
 Not all insects cause problems! Know what the
insect is and the plant’s/client’s level of tolerance
before treating.
 Consider cultural control and least toxic methods
first (hosing plant, soap solutions, oil sprays).
 Is the cost of cure worth the expense (example:
Protecting birch from the Bronze Birch Borer)?

78. Bronze Birch Borer

79. Treatment of insect problems:
 Not all insects cause problems! Know what the
insect is and the plant’s/client’s level of tolerance
before treating.
 Consider cultural control and least toxic methods
first (hosing plant, soap solutions, oil sprays).
 Is the cost of cure worth the expense (example:
Protecting birch from the Bronze Birch Borer)?
 If a few plants have an infestation that needs
treating, don’t broadcast spray the entire yard.

80. Spidermite Damage

81. Spidermite infestation on Spruce

82. Treatment of insect problems:
 Not all insects cause problems! Know what the insect is
and the plant’s/client’s level of tolerance before you treat.
 Consider cultural control and least toxic methods first
(hosing plant, soap solutions, oil sprays).
 Is the cost of cure worth the expense (ex. Protecting birch
from the Bronze Birch Borer)?
 If a few plants have an infestation that needs treating,
don’t broadcast spray the entire yard.
 Know the pest (where is it feeding) and the mode of action
of the chemical (contact or systemic).

83. Root weevil

84. Root Weevils

85. Pine Pitch Moth

86. Flatheaded Borer

87. Treatment of insect problems:
 Not all insects cause problems! Know what the insect is
and the plant’s/client’s level of tolerance before you treat.
 Consider cultural control and least toxic methods first
(hosing plant, soap solutions, oil sprays).
 Is the cost of cure worth the expense (ex. Protecting birch
from the Bronze Birch Borer)?
 If a few plants have an infestation that needs treating,
don’t broadcast spray the entire yard.
 Know the pest and the mode of action of the chemical
(contact or systemic).
 If repeat spraying is necessary, don’t always use the same
chemical.

88. Making the Diagnosis

89. Accurate diagnosis of plant
problems depends on:
 Observation of subtle differences from the normal

90. Accurate diagnosis of plant
problems depends on:
 Observation of subtle differences from the normal
 Knowledge of plants, soil, climate, cultural practices,
pests…

91. Accurate diagnosis of plant
problems depends on:
 Observation of subtle differences from the normal
 Knowledge of plants, soil, climate, cultural practices,
pests…
 Recent history of plants, site, cultural practices, climate

92. Accurate diagnosis of plant
problems depends on:
 Observation of subtle differences from the normal
 Knowledge of plants, soil, climate, cultural practices,
pests…
 Recent history of plants, site, cultural practices, climate
 Analytical approach to problem solving

93. Plant identification is critical as it can help
lead one to proper diagnosis; some diseases
are host specific.
(Example: Fireblight is only found in plants of
the family Rosaceae)

94. Knowledge of how a tree is put together and
functions is essential before one can determine
if some part of a tree's system is abnormal or
diseased.

95. Normal or diseased?

96. Normal: Varigated Boxelder

97. Normal?

98. Yes, Corkscrew Willow

99. Normal?

100. No, Fasciation

101. Normal?

102. No… 2,4-D damage

103. Disease Diagnosis: look for signs and
symptoms that can help with the diagnosis
 Sign - evidence of the pathogen itself
– mycelium
– fruiting body
– Pycnidia
– Oozing

104. Signs

105. Disease Diagnosis: look for signs and
symptoms that can help with the diagnosis
 Sign
 Symptom - Plant's response to the pathogen
(general appearance of the plant)

106. Symptoms

107. Diagnosis: Where to start?
 What part of plant is affected? (leaves, stem, roots, fruit)

108. Diagnosis: Where to start?
 What part of plant is affected? (leaves, stem, roots, fruit)
 What are the symptoms? (wilts, spots, chlorosis, curling...)

109. Diagnosis: Where to start?
 What part of plant is affected? (leaves, stem, roots, fruit)
 What are the symptoms? (wilts, spots, chlorosis, curling...)
 How many plants are affected?

110. Diagnosis: Where to start?
 What part of plant is affected? (leaves, stem, roots, fruit)
 What are the symptoms? (wilts, spots, chlorosis, curling...)
 How many plants are affected?
 Are they all the same type of plant, or many species?

111. Diagnosis: Where to start?
 What part of plant is affected? (leaves, stem, roots, fruit)
 What are the symptoms? (wilts, spots, chlorosis, curling...)
 How many plants are affected?
 Are they all the same type of plant, or many species?
 When did the symptoms first appear?

113. Lightening Damage

118. Diagnosis: Where to start?
 What part of plant is affected? (leaves, stem, roots, fruit)
 What are the symptoms? (wilts, spots, chlorosis, curling...)
 How many plants are affected?
 Are they all the same type of plant, or many species?
 When did the symptoms first appear?
 Is there a pattern to the symptoms?

119. Borer & Sapsucker
Borer exit holes
Sapsucker damage

120. Insect Damage Patterns
Root weevil
Leafcutter bee
Insect Damage Patterns

121. Diagnosis: Where to start?
 What part of plant is affected? (leaves, stem, roots, fruit)
 What are the symptoms? (wilts, spots, chlorosis, curling...)
 How many plants are affected?
 Are they all the same type of plant, or many species?
 When did the symptoms first appear?
 Is there a pattern to the symptoms?
 Are there any signs of insects or disease?

123. Sign
Symptom

124. Diagnosis: Where to start?
 What part of plant is affected? (leaves, stem, roots, fruit)
 What are the symptoms? (wilts, spots, chlorosis, curling...)
 How many plants are affected?
 Are they all the same type of plant, or many species?
 When did the symptoms first appear?
 Is there a pattern to the symptoms?
 Are there any signs of insects or disease?
 Any major changes in the vicinity of the plant in the last few
years? (excavation, grading ...)

126. Diagnosis: Where to start?
 What part of plant is affected? (leaves, stem, roots, fruit)
 What are the symptoms? (wilts, spots, chlorosis, curling...)
 How many plants are affected?
 Are they all the same type of plant, or many species?
 When did the symptoms first appear?
 Is there a pattern to the symptoms?
 Are there any signs of insects or disease?
 Any major changes in the vicinity of the plant in the last few
years? (excavation, grading ...)
 What were the cultural practices in the previous seasons?

132. Conclusions:
 Be observant
 Ask questions
 Don’t jump to conclusions (many pests and
diseases are secondary to a more serious
cultural problem)
 If you are unable to diagnose the problem,
do some research, talk to others, or refer it
to someone who can