1. Dr. Monica Elliott Ft. Lauderdale REC
BASIC
PLANT
PATHOLOGY
Dr. Monica Elliott Ft. Lauderdale REC

2. WHAT IS A
HEALTHY PLANT?
You can’t diagnose a plant problem without knowing how the plant looks when healthy!

5. Ask the right questions!
PLANTS DON’T TALK!
Information about a
plant sample must
come from person
managing the plant !
Ask the right questions!

6. Abiotic
vs.
Biotic

7. But, first rule out those pesky insects

8. Sooty mold is a fungus, but not a pathogen
Sooty mold is a fungus, but not a pathogen. It is feeding off insect excretions, such as honeydew.

9. Abiotic Biotic Injuries Pathogen is the problem Disorders
Pathogen is not causing problem
Biotic
Pathogen is the problem

10. A destructive physical occurrence to the plant
INJURY
A destructive physical
occurrence to the plant

11. INJURY Lightning strikes, Tire tracks Car or lawn equipment exhaust
NO pathogen!
Lightning strikes, Tire tracks
Car or lawn equipment exhaust
Animals - moles, armadillos, urine

14. DISORDER Interaction between the plant &
its environment that is usually
associated with imbalances of
physical or chemical require-
ments for plant growth.

15. DISORDERS Nutritional, usually deficiencies Air pollution
NO pathogen!
Cold or heat stress
Nutritional, usually deficiencies
Air pollution
Excessive rainfall or drought
Pesticide phytotoxicity

16. Cold Damage

17. Both too much and too little water can cause disease-like symptoms.
Drought
Oedema
Both too much and too little water can cause disease-like symptoms.

19. Sunburned palm leaf

20. Manganese deficiency

21. Manganese deficiency

22. Potassium deficiency

23. SPOTS & PATCHES A plant with a spot does not
automatically mean it has a
disease.
A yellow or dead patch in
the lawn does not mean there
is a disease.

26. Chinchbug damage

27. Typical injury from growth regulator type herbicide

30. DISEASE Interaction between the plant and a pathogen that disrupts
the normal growth and
appearance of the plant.

31. DISEASE Susceptible host Virulent pathogen Conducive environment
Three Components:
Susceptible host
Virulent pathogen
Conducive environment
Disease Triangle

32. Types of Pathogens Bacteria Phytoplasmas (mlo) Viruses Viroids Fungi
large
small

33. Most bacteria can be cultured on artificial media.
Phytoplasmas, viruses and viroids cannot be cultured on media.

34. Most fungi can be cultured on artificial media, but not all.

35. PATHOLOGY TERMS that is body of fungus.
MYCELIA: thread-like material
that is body of fungus.
SPORES: reproductive structures
of a fungus or bacterium

36. Bacteria – most enter through natural
openings or wounds
Viruses – transmitted through wounds
made mechanically or by vectors
Phytoplasmas – transmitted by vectors
Fungi – enter through natural
openings, wounds; or by mechanical
pressure or enzymes they produce

38. FUNGUS - FUNGI No chlorophyll, so no self energy
PATHOGEN: obtains energy
from living things
SAPROPHYTE: obtains energy
from dead things
SAME fungus can be BOTH a
pathogen and a saprophyte!

39. PATHOLOGY TERMS the fact it has a disease
SYMPTOMS: how plant expresses
the fact it has a disease
leaf spots, patches, tip die back, etc.
SIGNS: actual pathogen parts
associated with a diseased plant
spores, mycelia, conks, mushrooms

40. Signs of Disease

41. Signs of Disease

42. Signs of Disease

43. Plant
Organs
And
Functions
Disease
Symptoms

44. Symptoms spot – small, distinct lesion on leaf, fruit . . .
blight – spots that have coalesced or merged
together; more tissue being affected
rot – tissue is breaking down (fruit, roots);
usually mushy, but can be dry
wilt – plant droops due to water stress; can
be systemic (xylem) or due to root rot

45. Symptoms
gall – masses of undifferentiated growth; usually on stems or woody tissue
(branches) but can be on roots
- wart, clubroot, witches’-broom
canker – sunken lesions; usually on stems or
woody tissue
patches, decline – terms often used in
association with grasses (turf, grain crops)

46. Symptoms Caused by Bacteria
leaf spots and blights – water soaked,
greasy
soft rots of fruits
wilts (systemic – xylem)
gall (overgrowths/cell proliferation)
cankers

47. Symptom: Water soaked or greasy leaf spots

48. Symptom: Water soaked or greasy leaf blight

49. Symptom: Wilt
Symptom: Gall

50. Symptoms Caused by Viruses
dwarfing or stunting to some degree
mosaics – light green, yellow or white
areas intermingled with green – leaves
or fruits
ring spots – chlorotic or necrotic rings –
leaves, fruits or stems
are always systemic infections

51. Symptom: Dwarfing and Stunting

52. Symptom: Mosaic

53. Symptom: Ringspot

54. Symptoms Caused by Fungi
leaf spots and blights (including rust and
powdery mildew)
soft or dry rots of fruits, bulbs . . .
root rots
wilts (systemic – xylem)
overgrowths/cell proliferation –
clubroot, galls, warts, witches’-broom
scabs, cankers, patches and decline

55. Symptom: Leaf spots and blight

56. Symptom: Soft or dry rots

57. Symptom: Wilt

58. Symptom: Patches and Decline

60. PATHOLOGY TERMS does or does not cause a disease yes or no question
PATHOGENESIS: the pathogen either
does or does not cause a disease
yes or no question
VIRULENCE: severity level of the
disease that a pathogen causes
minimal damage vs. dead plant

61. Plant Samples Goal is to have plant sample arrive in
diagnostic laboratory looking like it did in
the field or landscape.
Keep roots moist, but do not place any other
tissue inside plastic bag.
Ask the right questions, fill out form
completely. It is critical to have background
information about the situation.

62. Plant Samples Ask the right questions: What is the plant?
Where is plant growing?
Is this sample typical?
When did symptoms appear?
Fertility and pesticide applications?

63. Plant Samples

64. Plant Samples Best samples are those that exhibit
progression of symptoms – e.g., leaf spot to
leaf blight to severely diseased plant.
Best to examine entire plant, if possible, as
root disease could be cause for leaf symptoms
Good pictures are useful, illustrating overall
symptoms and close-ups

65. Plant Samples Soil samples for disease diagnosis are useless.
Do not be afraid to tell a client that the sample is inadequate. We are not miracle workers!
It is better to make no diagnosis than to make the wrong diagnosis, especially if it is a valuable specimen or pesticides are required.

67. Three “Little” Steps 2. Identify the conditions
1. Identify the disease.
2. Identify the conditions
causing disease diagnosed.
3. Identify the management techniques
that will alter the disease-conducive
conditions causing disease diagnosed.
SureLook
Holmes

68. DISEASE Susceptible host Virulent pathogen Conducive environment
Three Components:
Susceptible host
Virulent pathogen
Conducive environment
Disease Triangle

69. Plant Disease Control Integrated Approach
Pathogen exclusion or sanitation
Plant resistance (genetic)
Cultural methods
Chemical methods

70. Plant Disease Control Pathogen exclusion - via regulation
- via ‘just don’t bring it home no
matter how cute it looks’ if it has a
spot, wilt, etc.

72. Plant resistance (genetic)
Plant Disease Control
Plant resistance (genetic)
Immunity is the rule in the plant
kingdom
Where immunity does not exist, plant
breeders have developed cultivars
with resistance to specific pathogens.

73. Plant Disease Control
Plant resistance (genetic)

74. Plant Disease Control Plant resistance (genetic)
- breeding for resistance to pathogen
- plant adaptation to site (right plant
for the right site concept)
- monoculture vs. mixed culture

75. Plant Disease Control Cultural methods - crop rotation
- host eradication (alternate hosts)
- improved plant environment,
especially water management

76. Plant Disease Control Cultural methods - sanitation of
tools, pots, shoes,
equipment, etc.

77. Plant Disease Control Chemical methods - seed treatments
- soil treatments/root drenches
- foliar sprays
- trunk injections

78. Plant Disease Control Chemical methods
critical to understand that chemicals do
not necessarily eliminate symptoms
observed
most chemicals prevent disease from
ever occurring or keep it from spreading

79. Plant Disease Control Chemical methods
ex: leaf spots don’t disappear, but old leaves with spots die and new growth is healthy and spot free
ex: rotted roots eventually die, but new roots are healthy and take their place to supply water and nutrients

80. Plant Disease Control Chemical methods “The label is the law.”
Pesticide labels must be followed, even by homeowners – safety to applicator and environment.
The site for application must be on the label – turf vs. ornamentals.

81. Some diseases do not have ANY control methods.
Plant Disease Control
Some diseases do not have ANY control methods.

82. Proactive vs. Reactive The single best method for controlling diseases
is to prevent them!