Oak Wilt

1. Oak wilt

2. What is Oak Wilt?
One of the most destructive tree diseases in the
United States.
Killing oak trees in central Texas in epidemic
proportions.
Caused by the fungus Bretziella fagacearum

3. Distribution in U.S.
Present in over 20 eastern and mid-western states

4. Where Is
Oak Wilt?
Present in 76
central and
west Texas
counties
Counties in Texas with oak
wilt cover an area larger
than CT, MA, MD, NH, NJ,
RI and VT combined!
Oak wilt first
identified in
Dallas, in 1961
in Texas

5. Oak wilt Impact

6. Urban Areas (< 1 acre)
Oak wilt may reduce urban
property values by 15-20%.

7. Rural Residential Areas
Loss of live oaks to oak wilt has greater economic
impact around ranch houses.

8. Rural Areas
Thousands of acres of live oaks
have become victims of oak wilt in
rural areas of Central Texas.

9. Suburban Areas (1-10 acres)
The many new “ranchettes” (<10 ac) in Central Texas have
increased incidence and impact of oak wilt.

10. Ecosystem Impact
Golden cheeked warbler
Also known as gold
finch of Tx
Endangered species
breeds in Central Tx
Range from Palo Pinto
county southwestward
along eastern and
southern edge of
Edwards Plateau
Only species with
breeding range
confined to Tx
Direct threat due to
loss of habitat (oaks
and juniper)

11. Ecosystem Impact
Ashe Juniper encroachment

12. Which Oaks are Susceptible to Oak Wilt?
All oaks (Quercus spp.) are susceptible to oak wilt!
Red oaks are extremely susceptible and play a unique role in
disease spread. Spanish (Q. buckleyi), Blackjack (Q. marilandica)
and Shumard (Q. shumardii) are present in central Texas.
White oaks tolerate oak wilt and rarely die from the disease.
These include Post (Q. stellata), Bur (Q. macrocarpa), Chinkapin
(Q. muhlenbergii), Lacey (Q. laceyi) and White Shin or Bigelow
(Q. breviloba v. sinuata).
Live oaks (Q. virginiana and Q. fusiformes) are intermediate in
susceptibility but are seriously affected due to their vast,
interconnected root systems that allow movement of the fungus
between trees.

13. Blackjack Spanish Shumard
The Red Oaks

14. The White Oaks
Bur
Post
Chinkapin
Lacey White Shin

15. The Live Oaks
Escarpment Coastal

16. Above Ground (long distance) via sap-feeding beetles.
Fungal spores are picked up from certain infected Red
oaks and carried to fresh wounds on other oak species.
New infection centers are started in this manner.
How is Oak Wilt Spread?
Sap Beetle
Fungal Mat
Fresh Wound
on Live Oak

17. Fungal Mats
Contain spores for spread by the beetle
Produced only on red oaks
Mycelial mats form under bark
Multiple mats per tree
Produce a sweet odor like rotting melons

18. Fungal mat production is accelerated by cool,
moist weather
In Texas trees killed in late summer may produce
mats the following spring.
Fungal Mats

19. Beetle Spread
Nitidulid Beetle

20. Beetle Spread
Beetles are only opportunistic
Sap feeding beetles
Attracted to sweet smelling odors- ripe fruit,
fresh wounds on trees
Peak beetle populations is in the spring
High temperatures limit beetle activity
Visit healthy trees rather than dead trees

21. Beetle Spread

22. How is Oak Wilt Spread?
Underground (localized) via interconnected root systems and
root grafts. This occurs primarily in Live oaks and is responsible
for the majority of spread and tree deaths in central Texas.
Root Grafts Live Oak Mott

23. Local Spread
Root grafts
live oaks and live oaks
live oaks and red oaks

24. How Fast Does Oak Wilt Spread?
Rate of spread via interconnected root systems
and root grafts is approximately 50’ to 75’ per
year.
1983 2 years later

25. How to Identify Oak Wilt
Foliar symptoms in Live oaks
Veinal chlorosis and/or necrosis

26. How to Identify Oak Wilt
Foliar symptoms in Red oaks
Bronzing or water soaking

27. How to Identify Oak Wilt
Pattern of mortality in Live oaks
Rapid defoliation.
Death in 3 to 6 months.
Eventual spread to adjacent trees.
No fungal mat formation.
~ 20% survival rate.

28. How to Identify Oak Wilt
Pattern of mortality
in Red oaks
Maintain dead leaves.
Death in 3 to 4 weeks.
Possible spread to adjacent trees.
Possible formation of fungal mats.
100% mortality (no survivors).

29. How to Identify Oak Wilt
Laboratory Diagnosis
(for all oaks)
Oak wilt may be confirmed by isolating the fungus
from diseased tissues in the laboratory.
TAMU AgriLife Extension-Texas Plant Disease
Diagnostic Lab
• https://plantclinic.tamu.edu/forms/
TAMU AgriLife Extension- Soil, Water, and Forage
Testing Lab
• https://agrilifeextension.tamu.edu/solutions/soil-
testing/

30. How to Manage Oak Wilt
Early detection and prompt action are essential for successful
management of oak wilt.
There are four primary approaches used to manage oak wilt:
These measures will not cure oak wilt but will
significantly reduce tree losses.
Prevention
Trenching
InjectionPlanting

31. How to Manage Oak Wilt
Prevention
Avoid wounding oaks from
February through June, and
regardless of season, paint all
pruning cuts and other wounds
immediately.

32. How to Manage Oak Wilt
Destroy infected Red oaks (burn, bury
or girdle) to prevent fungal mat
formation.

33. How to Manage Oak Wilt
Transport and use
dry, well-seasoned
firewood only.
Leave unseasoned
wood on site at least
one full year before
transporting.
Do not store infected
firewood near
uninfected trees.
Cover wood with
clear plastic and bury
the edges to prevent
insects from leaving
the pile.

34. How to Manage Oak Wilt
Used to disrupt root connections
and stop the localized spreading
of the disease.
Trenching

35. How to Manage Oak Wilt
Trenches must be placed a minimum distance of
100’ from the disease and at least 4’ deep
(sometimes deeper) to halt spread.
Diseased Tree
Healthy Tree
Trench

36. How to Manage Oak Wilt
Removing all oaks, especially
healthy oaks along barrier, can
improve trenching effectiveness.
Pushing

37. How to Manage Oak Wilt
Injection
Used to protect high-value
Live oaks in advance of an
expanding oak wilt center.
Best candidates for treatment
are healthy Live oaks within
75’ to 150’ from symptomatic
trees.
Injection does not stop root
transmission of the fungus.

38. How to Manage Oak Wilt
Treatment success depends
on the health of the tree,
application rate, and
injection technique.
Injection should only be
performed by trained
applicators.

39. How to Manage Oak Wilt
Several steps are involved in
the injection process from
mixing the fungicide solution
to connecting the injection
harness to the tree.
The services of a professional
arborist may be required to
assure proper injection.

40. How to Manage Oak Wilt
Planting
Select trees that are native or
adapted to central Texas.
Select trees that are resistant
or immune to oak wilt.
Avoid planting monocultures;
create diversity in the
landscape.
Avoid wounding oaks during
planting.

41. Commonly Confused with…
• Drought
• Hypoxolyn canker

42. What is Drought?
The absence of precipitation for a periods of
time sufficient to deplete soil moisture and
injure plants
Drought stress results when water loss exceeds
the ability of the plant’s roots to absorb water
and begins to interfere with normal plant
processes

43. Symptoms of Drought Injury
• Loss of turgidity – wilting
• Chlorotic leaves - yellowing
• Leaves may appear dull
• Leaves become misshapen
• Browning and/or loss of leaves
• Loss of fine feeder roots
• Branch dieback from top down and from
outer to inner branches
• Decreased defenses against insects and
disease

44. Leaf symptoms from drought
Interveinal chlorosis Tip burn

45. Branch dieback

46. Other drought related problems
• Increased plant susceptibility to pests:
Spider mites, Borers, Twig beetles, aphids
• Increased susceptibility to diseases:
Armallaria root rot, Ganoderma root rot,
Hypoxylon canker, Bacterial wetwood,
and a host of other wood rot fungi

47. Hypoxylon canker

48. Disease spread
• Spores are produced from fruiting structures
and spread by wind.
• Spores enter tree through injuries to limbs
and trunk
• Disease commonly remains dormant until the
tree experiences stress sufficient enough to
reduce tree defense mechanisms and allow the
disease to colonize the tree

49. Hypoxylon Canker Symptoms
• Change of foliage color in early summer or
spring
• Branch dieback, initially in one branch, then
spreading to the whole crown
• Bark sloughs off exposing large masses of
brown dusty spores that transition to a
grayish surface with black fruiting structures
• Infected wood has black streaks or patterns
throughout the wood

50. Control Options
• Prevention is achieved by maintaining tree
health
• Avoid injury to trunk, limbs and roots
• Never apply fill soil around the trees
• Avoid compaction of soil in root zone
• Do not alter drainage around trees
• Avoid injury to root systems

51. Tree Insects & Disease

52. Damage To Trees Can Be
Caused By:
• Diseases
• Insects
• Environmental Factors
• Animals or human Activity
• Toxic Chemicals
• Combination of two or more

53. DISEASES

54. Pecan Scab

55. Pecan Scab
Hosts: Pecan
Time of Year: infected in May to June
Symptoms: visible lesions develop in 7 to 14 days. Lesions
are generally circular, range in size from pinpoint to about
one-quarter inch in diameter. They are light brown to black
Effects: Poorly filled pecans and possible premature nut drop
Control: Use resistant varieties of pecan, mix varieties in an
orchard, sanitation, Fungicide applications at budbreak.

56. Powdery Mildew

57. Powdery Mildew
Hosts: most local plants, especially crepe myrtle and cedar elms
Time of Year: late summer
Symptoms: a white powdery mold on leaves or buds, may cause
distortion of leaves when severe.
Effects: Yellowing of leaves and death of tissue may result in
premature leaf drop.
Control: Gather up fallen leaves in autumn and destroy them, may use
fungicide sprays when first white patches are noticed. (potassium
bicarbonate, benomyl, wettable sulfur, funginex, folpet,
cycloheximide, pipron)

58. Anthracnose

59. Anthracnose
Hosts: various hosts including sycamore, oak, ash, and dogwood
Time of Year: cool season disease of spring & fall
Symptoms: irregular patches of dead leaf tissue, blackened
bases of the leaf stem, cankering of the branch at the base of leaf
stem, and shoot dieback.
Effects: May cause decline or death in trees
Control: Destroy fallen leaves and twigs, prune dead wood and
large infected limbs as the fungus can overwinter on these
parts.Tiophanate-methyl, cupric hydroxide,or chlorothalonil,
may be applied at bud-break and 10-14 days later.

60. Bacterial Leaf Scorch

61. Bacterial Leaf Scorch
Hosts: various species including elm, red maple, mulberry, oak,
and sycamore
Time of Year: mid-summer
Symptoms: yellowing and then browning of the edge of all the
leaves on one shoot of a tree, leaves will hang on until fall
Effects: Growth of damaged trees slows and diseased limbs start
to die back each year.
Control: Injecting bactericides into the trunk of lightly damaged
trees will suppress symptoms but will not eradicate the bacteria.
Fertilizing and irrigating may prolong the life of diseased trees.

62. Oak Leaf Blister

63. Oak Leaf Blister
Hosts: oaks, especially red oaks
Time of Year: spring
Symptoms: blisters scattered over upper leaf surface with
corresponding gray depression on the lower surface.
Effects: Hinders appearance of tree.
Control: Single application of chlorothalonil or mancozeb
in early spring just before the buds begin to swell will
control the disease.

64. OTHER COMMON
PROBLEMS

65. Lightning Strike

66. Mistletoe • Parasite common to
many trees, especially
sugar hackberry and
cedar elm.
• Draws water and
nutrients from the
host tree.
• Rarely kills trees but
causes structural
problems
• Spread by birds and
rain when in seed.

67. • Prune branches with
mistletoe infestations.
• Physically remove mistletoe
growths.
• Florel
growth hormone
is available spray
for mistletoe
control. Timing
is critical!

68. INSECTS & PESTS

69. Defoliating insects
• Cankerworms and caterpillars
• Orthopterans
– Grasshoppers
– Katydids
– Walking sticks

70. Cankerworms
Spring Cankerworm Fall Cankerworm

71. Cankerworms
Hosts: red & white oaks, maples, elms, hickories, ash, and cherry
Time of year: Spring (May & June), Fall (after a freeze)
Symptoms: Small holes in leaves are evidence of young larvae
feeding on foliage. Older larvae will consume the entire leaf
except the midribs and major veins.
Effects: Growth loss, mast reduction, and possible mortality
when coupled with other stressors.
Control: Other insects and birds will help in the control. Placing
sticky bands around the trunks of high value trees can help trap
the females as they climb higher into the tree to lay eggs.
Bacterial thuringiensis is shown to help control cankerworms.

72. Fall Webworm
• Common throughout US &
southern Canada.
• Host include over 100
species of broadleaf trees.
• More nuisance than threat
to tree health.
• Two forms in Texas,
redheaded and blackheaded.
• Redheaded form builds
larger and more dense webs.
• Young larvae skeletonize
the upper leaf while older
ones devour the entire leaf.
• Adult moths usually appear
in May.

73. • Female adults lay several
hundred eggs on underside
of leaves.
• Egg masses appear as
white, cottony patch on
leaf.
• Up to 4 generations per
year in southern Texas.

74. Controls:
• Prune nests from high
value trees and destroy
• Chemically treat with Sevin
or Bacillus thuringiensis
(B.t.)

75. Orthopterans

76. Orthopterans
Hosts: Hardwoods
Time of Year: summer
Symptoms: Entire leaf blade, except stout veins are
eaten. Trees may be defoliated twice in one year.
Effects: Mortality may occur if continuous defoliation
occurs year after year.
Control: Natural predators (birds)

77. Squirrels
• Feed on tissue in oaks and pecans when other food sources are scarce.

78. Squirrels
Hosts: oaks, pecans, some conifers
Time of year: Spring, Fall
Symptoms: Flagging will occur throughout the canopy
of the tree. Upon closer inspection can possibly see teeth
marks from the chewing.
Effects: Twigs will die off in canopy, can kill small
trees.
Control: Good luck!

79. Sucking Insects
• Aphids
• Lace bugs
• Scales

80. Aphids
Left: oak leaf aphid, Above: wooly ash aphid

81. Aphids
Hosts: hardwoods and conifers
Time of Year: spring, summer
Symptoms: feed on undersides of leaves causing stunting,
curls or folds in leaves. Also look for leaf discoloration,
dieback or flagging of newly formed terminals, and early
leaf drop
Effects: May distort foliage, cause terminal dieback, reduce
vitality, weaken the tree, and cause branch or crown dieback.
May also see sooty mold and ants frequenting tree.
Control: Parasites and predators, insecticides may be used
to protect high value trees.

82. Lace Bugs

83. Lace Bugs
Hosts: hardwoods (sycamore, oak, elm, hackberry)
Time of Year: summer
Symptoms: Infested leaves will have chlorotic spots or
flecks on the upper side.
Effects: Leaves may be discolored and performing little
photosynthesis and may fall from tree
Control: Natural enemies, chemical controls are usually
only used on shade and ornamental trees.

84. Scales

85. Scales
Hosts: hardwoods and conifers
Time of Year: spring, summer
Symptoms: stunting of leaf or shoot growth, leaves turning
yellow or red, early leaf drop or dieback
Effects: Heavy infestations may kill trees. Sooty mold and
ants frequenting trees.
Control: Natural enemies, chemical controls are used on
high value trees and are most effective on immature scales.

86. Gall Forming Insects
Oak Apple gall
Horned wasp gall

87. Diagnosis of Problem:
D ISTRIBUTION OF DAMAGE
I DENTITY OF TREE
S ITE TYPE, CONDITIONS, & CHANGES
E NVIRONMENTAL CONDITIONS & OTHER CHANGES
A GE OF TREE NOW OR AT PLANTING
S YMPTOMS
E XTRANEOUS MATTER (INSECTS, FUNGI, EXUDATES, ODORS)
D EAD BARK, DISCOLORED WOOD
T IME OF ONSET OF DAMAGE & ITS PROGRESS WITH TIME
R OOT CONDITION
E VIDENCE – REVIEW BEFORE MAKING A DIAGNOSIS
E XTRA EVIDENCE – SEE WHERE POSSIBLE, IN ORDER TO CONFIRM

88. Questions
rmcgregor@tfs.tamu.edu