CHAPTER 8: FOREST PATHOLOGY

1
CHAPTER 8FOREST PATHOLOGY

• FOREST PATHOLOGY ? study of diseases in trees
  (and fiber deterioration after harvest)
• DISEASES ? losses as high as 35 of growth
• DISEASE CONTROL STRATEGIES used only if economic
  loss at least equals treatment costs

2
DISEASE OR INJURY?

• DISEASE ? disturbance of normal metabolism or
  structure involves continuous irritation by
  abiotic or biotic causal agent
• INJURY affects plant only once or intermittently

3
TORNADO INJURY
4
CAUSES OF DISEASE ABIOTIC (NON-INFECTIOUS)
AGENTS

• Moisture temperature extremes
• Nutrient excess or deficiency
• Toxic substances (e.g., air pollution)

5
CAUSES OF DISEASE BIOTIC (INFECTIOUS) AGENTS

• VIRUSES
• MYCOPLASMAS
• BACTERIA
• FUNGI (most common biotic disease agent in trees)
• PARASITIC PLANTS
• NEMATODES (EELWORMS)

6
CAUSES OF DISEASE VIRUSES

• Relatively unimportant in forestry
• More significant with trend to plantation
  forestry?

7
CAUSES OF DISEASE MYCOPLASMAS

• Smallest free living organisms
• Relatively unimportant in forestry
• BUT a mycoplasma-caused disease impeded progress
  against Dutch elm disease

8
CAUSES OF DISEASE BACTERIA

• Relatively unimportant in North American forestry
• Poplar canker serious in Europe
• May cause wetwood (abnormal heartwood)
• Decay pioneers (pre-fungal wood decay)
• Agrobacterium important for biotechnology (a
  natural plant genetic engineer)

9
WETWOOD -- TURKEY OAK
10
CAUSES OF DISEASE PARASITIC PLANTS

• E.g., DWARF MISTLETOES
• Major problem in western conifers
• Stunts growth (witches-broom)
• Death of leader, branches, tree
• Control difficult (physical removal)

11
WITCHES BROOM ON SPRUCE
12
CAUSES OF DISEASE NEMATODES(MICROSCOPIC
EELWORMS)

• IN PLANTATIONS NATURAL FORESTS little
  information in North America
• IN NURSERIES root dieback, plant stunting,
  mortality

13
CAUSES OF DISEASE FUNGI

• THE MOST DESTRUCTIVE DISEASE-CAUSING ORGANISMS IN
  FOREST TREES
• Saprophytes on dead organic material (e.g.,
  heartrot)
• Parasites on living plants (e.g., white pine
  blister rust ? stem girdling)

14
CAUSES OF DISEASE FUNGI (continued)

• HEARTROT (CAUSED BY SAPROPHYTES)
• gt70 of disease losses in forests
• Little effect on vigor/mortality (heartwood is
  dead)
• Causes structural weakness (increases storm
  damage)
• Fungi enter trees through infection courts
  (wounds or damage)
• Decay increases with tree age, damage

15
HEARTROT FUNGI

• BROWN ROT FUNGI
• Utilize cell wall cellulose
• Wood fiber become economically useless
• WHITE ROT FUNGI
• Utilize cell wall cellulose and lignin
• Wood becomes useless for construction
• Fiber usually OK for pulp/paper

16
HEARTROT CONTROL

• CONTROL IS SILVICULTURAL OR PREVENTIVE (There Is
  No Cure)
• Shorten rotation age
• Avoid logging injuries to residual trees
• Control stand density
• Remove diseased trees early
• Thin stump sprouts early

17
FRUITING BODIES ON ASH
18
FRUITING BODIES
19
CAUSES OF DISEASE FUNGI (continued)

• ROOT ROTS
• Many types, may kill trees
• Spread underground root-to-root or via fungal
  mycelium
• Control difficult
• Chemical treatment of cut stumps
• Biological control (non-pathogenic competitors)

20
ROOT / BUTT ROT FRUITING BODIES
21
ROOT ROT DAMAGE IN WESTERN RED CEDAR
22
CROWN SYMPTOMS OF ROOT DISEASE
23
ROOT DISEASE STAND DAMAGE
24
CAUSES OF DISEASE FUNGI (continued)

• CANKERS
• Localized death of stem cambial tissues
• May kill by girdling stem (e.g., chestnut blight)
• May decay wood
• May reduce wood quality
• Control difficult or unknown

25
CHESTNUT BLIGHT
26
CAUSES OF DISEASE FUNGI (continued)

• VASCULAR WILT DISEASES
• Fungi grow in xylem vessels
• Reduces water conduction leads to tree death
• Primarily in angiosperms (e.g., Dutch elm
  disease, oak wilt)
• Infections via soil, root grafts, insects (e.g.,
  Dutch elm disease carried by bark beetles)

27
OAK WILT
28
CAUSES OF DISEASE FUNGI (continued)

• RUST FUNGI
• May attack leaves and conifer stems cones
• Many require two different hosts

29
RUST FUNGI

• E.g., WHITE PINE BLISTER RUST
• Introduced from Asia via Europe 1900
• Most serious disease of white (soft, 5-needle)
  pines
• Branch stem cankers girdle and kill
• Eliminating alternate host (currants/gooseberries)
  failed as a control strategy
• Breeding for resistance may be best hope -- (but
  pathogen may evolve in response)

30
WHITE PINE BLISTER RUST ON EASTERN WHITE PINE
31
WHITE PINE BLISTER RUST IN MONTANA
32
RUST FUNGI

• E.g., FUSIFORM RUST (SOUTHERN PINES)
• Loblolly slash pines are killed by cankers
• Longleaf shortleaf pines resistant or immune
• Native to southern U.S., but disease rare before
  1900
• Trend ? more loblolly slash pines
• Trend ? more oaks (the rusts alternate host)
• Now a costly epidemic
• Partial control achieved by
• Fungicides (in nurseries)
• Planting seedlings from resistant provenances

33
FUSIFORM RUST ON LOBLOLLY PINE
34
FUSIFORM RUST WIND BREAKAGE AT CANKER
35
FUSIFORM RUST SEEDLING INOCULATION
36
FUSIFORM RUST ON OAK LEAF (ALTERNATE HOST)
37
FUSIFORM RUST RELATIVE DISEASE SEVERITY
38
Melampsora RUST ON COTTONWOOD
39
CAUSES OF DISEASE FUNGI (continued)

• DAMPING-OFF (occurs in seedlings)
• Main obstacle to raising conifer seedlings
• May kill before seedling emerges from soil
• Emerged seedlings infected at soil surface
  seedlings topple
• May cause root rot
• Fungicide treatment often necessary

40
DAMPING-OFF
41
DAMAGE TO KILLED OR INJURED STANDING TIMBER

• Sapwood decays rapidly in dead trees
• Microorganisms insects first
• Wood-destroying fungi next
• Heartwood decays last
• Younger trees deteriorate faster (less heartwood
  than in older trees)
• Salvage harvest must occur within a few years
  unless trees were large (overmature) before death

42
DAMAGE TO FOREST PRODUCTS

• CONTROL OF STAINS AND DECAY REQUIRES PREVENTION,
  e.g.
• Rapid drying (air seasoning, kilns)
• Fungicides, wood preservatives
• Excluding oxygen from logs (e.g., with water)

43
DISEASE TRIANGLE(Requirements For Disease)
Susceptible Host
Virulent Pathogen
Favorable Environment
44
DISEASE TRIANGLE(Requirements For Disease)
Susceptible Host
Virulent Pathogen
Favorable Environment
ENVIRONMENTAL STRESSES CAN PREDISPOSE TREES TO
DISEASES CAUSED BY PATHOGENS E.g.,
drought E.g., freezing
45
DISEASE MANAGEMENT

• GOAL reduce damage to acceptable level
• FOCUS prevention of disease if possible
• FOCUS is NOT on cure
• INTEGRATED PEST MANAGEMENT (IPM) use of
  silvicultural indirect management techniques
  (disease management, not disease cure)