The document provides information on common ornamental plant diseases caused by fungi, bacteria, and other pathogens. It describes the symptoms, signs, life cycles and management strategies for various diseases that affect leaves, flowers, stems, and roots of ornamental plants. Key diseases discussed include powdery mildew, botrytis, rusts, fire blight, bacterial blight, crown gall, cankers, and vascular wilts. The document emphasizes integrated pest management approaches for disease control, such as sanitation, improving plant health and removing diseased plant material.

1. Ornamental Plant Diseases
Commercial Pesticide Applicator
Exam Preparation
Laura Pottorff, Colorado State
University Adams County

2. Diseases Caused by Fungi
• If the cause affects leaves/flowers only
– Fungi
• Powdery mildew
• Botrytis
• Rust
• Anthracnose
• Marsonnina
• Apple scab
• Septoria leaf spot

3. Common characteristics of fungi
that affect leaves/flowers
• Live above ground
• Spread via wind, water, insects
• Often require a water film on leaf surface to
germinate and penetrate plant tissue.
• Often overwinter on plant debris.

4. Powdery mildew on poinsettia

5. Powdery mildews
• Produces talcum powder-like growth on leaf
surface. (Sign)
• Many, many plants are susceptible (even
weeds).

6. Powdery mildew
• Example:
– Western sand cherry

7. Powdery mildew
• Fungus overwinters on
leaf debris
• Favored by
– shade, poor air
circulation

8. Powdery mildew management
• Clean up leaf debris.
• Improve air circulation with selective
pruning.
• Fungicides
– Potassium bicarbonates, Oils, Sulfur, Neem
– Cleary’s 3336, Eagle, Bayleton

9. Botrytis (Gray mold)
• Fungus produces gray mold on surface of
flowers, fruit, leaves, and stems.

10. Botrytis
• Favored by • Management
– high humidity – Clean up debris
– Poor air circulation – Good plant culture
– Wounded or weakened – Avoid over watering
tissue – Avoid over fertilization
– Many of the same
fungicides as for
powdery mildew
control *follow label
directions.

11. Rust diseases
• Two types
– single host
• sunflower rust
• snapdragon rust
• rose rust
– two hosts
• Juniper - Hawthorn rust

12. Juniper - Hawthorn Rust
• Rocky Mt. Juniper
– Galls

13. Juniper - Hawthorn Rust
• Hawthorn
– Leaf spots

14. Cedar/apple rust leaf Cedar/apple rust “spores” on leaf
spots on crabapple underside of crabapple
June-August
August - April
April - June
Cedar/apple rust
gall on juniper
Cedar/apple rust
“spore horns” on
juniper

15. Juniper Hawthorn Rust
Management
• Separate hosts
• Prune out galls on juniper
• Clean up leaves in autumn on hawthorn
• Fungicides
– Juniper
• Bordeaux mixture
– Hawthorn
• Bayleton, Cleary’s 3336

16. Day Lily Rust
• Native to China, • Main way of spread
Japan, Korea, Taiwan, – Airborne spores
Russia
• Be on the look out
– Not yet in Colorado
• Heteroecious rust
– Day lily
– Patrinia (lily family)
– Hosta? (lily family)
Diagram: M. Hahn and K.
Mendgen, Konstanz
University

17. Day Lily Rust
• First found in U.S. in December 2000
• Due to nature in which plants are moved
about there is concern
• We do not know how serious this disease
will be

18. Day Lily Rust

19. Daylily rust
• Symptoms

20. Day Lily Rust
• Not Daylily rust

21. Day Lily Rust
• Signs

22. Day lily Rust management
• Fungicides known to be affective against rust and
labeled for day lily
– Banner Maxx (propiconazole)
• home owner version
– Fertilome liquid systemic fungicide
– Contrast (flutalonil)
– Heritage (azoxystrobin)
– Systhane (myclobutanil)
– Daconil
– Mancozeb

23. Apple Scab (Venturia inequalis)
• Hosts: Apple, Crabpple, Malus spp.
• Symptoms

24. Apple Scab
• Favored by • Management
– Wet spring – Clean up leaf debris in
fall
– Poor air circulation
– Fungicides normally
– Certain varieties more
not needed.
susceptible
• Radiant crabapples

25. Anthracnose
Anthracnose

26. Anthracnose
• Anthracnose is a term • Hosts: oak, sycamore,
for a type of leaf spot ash, and many other
disease. ornamentals
• Blotchy, necrotic
lesions.
• Normally not serious.
• Outbreaks dependent
on spring weather
conditions.

27. Anthracnose
• Life cycle:
– fungus overwinters on
leaves that fall to the
ground in autumn.
– Spores become active
in spring and blow up
to newly emerging
leaves.
– Favored by spring
moisture.

28. Anthracnose
• Management:
– clean up leaf debris
– allow for better air movement
– fungicides are normally not needed

29. Marsonnina leaf spot on aspen

30. Marsonnina leaf spot
• Host: Aspen
• Damage: Yearly infestations may weaken
tree. Causes premature leaf drop.
• Normally not a concern in native areas
(except for ruining fall color)
• In landscaped areas may detract from look
of tree.

31. Marsonnina leaf spot
• Symptoms
– dark black spots on leaves

32. Marsonnina leaf spot
• Life cycle:
– Fungus overwinters on leaf debris
– Will spread to newly emerging leaves in the
spring.
– Symptoms visible in late summer - fall.

33. Marsonnina leaf spot
management
• When symptoms are visible (late summer):
– Clean up leaf debris
– IT IS TOO LATE TO SPRAY
• If a fungicide application is warranted
– Apply in the spring during bud break
• Cleary’s 3336
• 26GT

34. Septoria leaf spot
Photos:Government of British
• Hosts: Cottonwood,
Columbia- Forest Services
maple and dogwood
• Round leaf spots with
dark margin
• Fruiting structures
within tan interior of
leaf spot
Fruiting structures

35. Integrated Pest Management of
Fungal Leaf Spots
• Clean up leaf debris (sanitation)
• Avoid moisture on leaf surface
• Decrease relative humidity
• Improve air circulation
• Is the plant located in the “right place”
• Optional
– Funigicides

36. Examples of Alternative Fungicides
Labeled for Most** Leaf Spots
• **READ THE LABEL!!!
– Copper sulfate (anthracnose, powdery mildew,
juniper tip blights)
– Neem oil (Triact, Rose Defense) for powdery
mildew
– Potassium bicarbonate (Kaligreen, First Step)
for powdery mildew
– Sulfur (powdery mildew, black spot)

37. How do we get rid of it?
(Integrated Pest Management)
• If the cause affects leaves/flowers (and
stems) only
– Bacteria
• Fire blight

38. Spring - Summer
Fire blight cycle
Shepherd’s crook
Canker

39. Fire blight cycle
Summer - Winter

40. Integrated Pest Management of
Fire blight
• Prevention • Control
– Resistant varieties – Removal of
• Crabapples
symptomatic branches
– Centurion
(disinfect tools
– David
between each cut)
– Indian Summer
– Molten Lava
– Pesticides
– Profusion
• Streptomycin sulfate
– Robinson
(for agricultural use
– Biological control
only)
• Blight Ban (Pseudomonas
• Copper
flourescens)

41. Bacterial blight
(Pseudomonas)
• Hosts: Lilac, • Symptoms: blackened
stems, petioles, and
Cotoneaster
leaves. Shepherds crook.
• Occurs in spring
• Commonly confused
with frost injury
Photos from Cornell University

42. Bacterial Blight
• Management
– Dry spring weather is a natural control
– Prune out diseased branches, disinfecting
pruning tools between each cut.
– Results from chemical control are often
unsatisfactory

43. Bacterial Wetwood
• Hosts: Cottonwood, • Callus formation
Siberian Elm, Willow retarded
• Smelly, ooze running
down trunk

44. Bacterial wetwood
• No effective methods exist to eliminate
wetwood disease. Preventing damage and
stress to a tree's roots and stem is the best
way to avoid a serious wetwood problem.
Drought conditions increase wetwood
problems, so it is important that the tree
receives adequate water, especially during
spring and summer months.

45. Crown Gall
Agrobacterium tumefaciens
• Hosts: Stone and
pome fruits, roses,
cottonwood, junipers,
grapes.
• Symptoms: wilting,
gall at crown line or
on roots.

46. Crown gall management
• Bacterium is soilborne
• Remove plant
• Replant with nonsusceptible species
• Avoid root wounding

47. How do we get rid of it?
(Integrated Pest Management)
• If cause (who) only affects stems
– Fungi
• Cankers
Canker caused by
bacteria
Canker caused by
fungus

48. Dieback caused by?

49. So What???
Cytospora?
Fruiting structures = fungus
Thyronectria?

50. Dieback caused by?

51. Girdling

52. Integrated Pest Management for
Canker diseases
• Remove affected branch.
• Remove entire plant if on main stem.
• Optional
– Improve health of plant
• Fungicides are not effective

53. Vascular wilts
• If the cause (who) only affects internal plant
tissues
– Fungi
• Dutch Elm Disease (Vectored)
• Verticillium wilt (soilborne)

54. Vascular wilt disease
– Can also move
• Dutch elm disease
between trees through
– Vectored by the elm
root graphs
bark beetle

55. Integrated Pest Management for
Dutch Elm Disease
• Prevention • Control
– Resistant varieties – Remove tree
– Fungicide injection – Trench potential root
graphs
• Arbotect
(benzimadazole) – Control vector
• Alamo
(propioconazole)
Fungicide
injection
Photo by Lise
Mahnke

56. Vascular Wilt Disease
• Verticillium wilt • Gray to olive brown
vascular streaking
– Soilborne fungus
– Many types of plant
hosts
• Woody
• Herbaceous

57. Integrated Pest Management of
Verticillium Wilt
• Prevention • Control
– Rotation of host plants – Removal of tree (not
mandated)
– Resistant tree varieties
– Fungicides not
• Hawthorn
effective
• Honey locust
• All conifers
• Apple/Crabapple/Pear
• Sycamore
• Oak
• Willow
• Mt Ash
• Linden

58. • Dieback caused by?

59. Girdling root

60. Problems affecting roots
• If cause (who) only affects roots
• Biotic
– Fungi (Pythium, Rhizoctonia)
• Abiotic
– Root girdling
– Oxygen starvation
– Etc.

61. Symptoms of root rot
• Soft brown mushy roots
– Sloughing of cortex

62. Integrated Pest Management for
Fungal Root Rots
• Biotic
– Avoid over watering/improve soil drainage
– Destroy severely affected plants
– Optional
• Fungicides

63. Fungicides Labeled for Most**
Root Rot Fungi
• **READ LABEL DIRECTIONS
– Rhizoctonia or Fusarium
• Iprodione (Chipco 26019)
• azoxystrobin (Heritage)
• Thiophanate methyl (Cleary’s 3336)
• Trifloxystrobin (Compass)
• Gliocladium virens (Soilguard) - Biological

64. Fungicides Labeled for Most**
Root Rot Fungi
• **READ LABEL DIRECTIONS
– Pythium or Phytophthora
• Metalaxyl (Subdue or Chipco Signature)
• azoxystrobin (Heritage)

65. Abiotic Diseases
• environmentally induced disease
• the precursors or primary plant problems
– lead to plant stress/weakness
– lead to invasion of insects and disease

66. Affecting Roots
• Soil condition and drainage is the primary
problem

67. Affecting roots (and leaves)
• Abiotic- 80% of all
landscape plant
problems fall this
category

68. Affecting Roots (and leaves)
• oxygen starved roots

69. Colorado Blue spruce located on south
facing slope in urban landscape.

70. Plant siting
• Natives and adapted
non natives can be
Ginnala maple
planted together.
– Watch that moisture
regimes are similar
Yucca

71. Affecting Roots
(leaves symptomatic)
• Nutrient deficiency
– brought on by
• soil condition
• excess moisture
– oxygen starvation

72. Affecting roots
(leaves symptomatic)
• Leaf scorch
– an imbalance between
water uptake and loss.

73. Affecting Leaves
External “pressures” typically
“blow” in.

74. Leaves affected
– Freeze

75. Affecting leaves
• 2,4-D herbicide injury to Ginnala maple

76. Is a Chemical Necessary?
– Is the host plant valuable?
– Is the pest/disease properly identified?
– Is the disease life- or health-threatening?
– Does this plant have a history of disease?
– Are effective, legal treatments available?
– Will one or two applications suffice?
– Have cultural control practices been used?