TREE & SHRUB
DISEASES
OF
TEXAS
Compiled by: THOMAS Isakeit, Ext. Plant Pathologist
Modified for use in Fort Bend by: Vince Mannino, CED-FBC
FUNGAL
DISEASES
AFFECT A WIDE
HOST RANGE
AND CAUSE
DEATH
WOOD DECAY FUNGI
 Mature trees affected
 Gradual decline over several years
 Wounds and environmental stress
(e.g. drought) are pre-disposition
factors
 Diagnosis: presence of fruiting
bodies (conks)
WOOD DECAY FUNGI
WOOD DECAY FUNGI
LIVE OAK IN A
NATIVE STAND
AVOCADO IN AN ESTABLISHED
ORCHARD
DIAGNOSIS OF GANODERMA
THE PRESENCE OF FRUITING BODIES (CONKS) OF GANODERMA
LUCIDUM ON TREES THAT ARE STILL ALIVE IS DIAGNOSTIC FOR
THIS SPECIES OF WOOD DECAY FUNGUS. IT CAN ALSO OCCUR ON
DEAD TREES AS A SAPROPHYTE.
OTHER WOOD ROT FUNGI
A CONK ON A LIVING TREE IS
EVIDENCE OF INFECTION !
GANODERMA LUCIDUM seems to
be the most prevalent species in
south and central texas, but other
species of wood decay fungi have
been identified (INONOTUS
RICKII shown here).
WOOD ROT FUNGUS - DIAGNOSIS
sometimes conks may not be
produced on infected trees
until they are dead. the
presence of rhizomorphs
(white or brown fungus
strands on the root surface)
on a tree that is gradually
dying may support a tentative
diagnosis of fungal infection
WOOD DECAY FUNGI
 There is no treatment once trees are infected.
 Prevention: keep trees watered, try to
minimize other stress.
 Prevention: proper pruning technique to
promote rapid wound healing. there is no
benefit to pruning paint.
 Wood decay fungi may be transmitted by
wood-boring beetles
 A living, infected tree may be in danger of
falling!
COTTON ROOT ROT
 Rapid death (weeks or within season) of
trees and shrubs of any age
 Symptom onset during summer months
 Diagnosis: microscopic examination of
fungal strands on roots, presence of spore
mats on soil surface (not always produced)
 If cotton can grow in the vicinity, then so
can cotton root rot!
COTTON ROOT ROT
COTTON ROOT ROT
ASH TREE
&
CAPE HONEYSUCKLE
COTTON ROOT ROT
Progression of cotton root rot on Pittosporum
COTTON ROOT ROT
Spore mats of
the fungus are
sometimes
produced on
the soil
surface near
the dying
plant, in moist,
shaded areas
COTTON ROOT ROT
 No treatment for infected plants
 Fungus survives indefinitely in soil &
doesn’t move; infection occurs when
plant roots grow to it
 Monocot plants (e.g. agave, banana,
palms) are immune
 Dicot plants vary in resistance: see tx
plant diseases handbook (b-1140) or tx
ag. expt. station bulletin 527
DISEASES CAUSED BY
FUNGI AND OTHER
ORGANISMS THAT
CAUSE DEATH AND HAVE
A MORE LIMITED HOST
RANGE IN TEXAS
FUNGAL CANKER AND DIEBACK
 Caused by several species of fungi,




with some host specificity
Fungi are “weak” pathogens
Host predisposed by injury and/or
environmental stress
Diagnosed by the presence of the
fungus to differentiate from insects
Treatment: corrective pruning
FUNGAL CANKER AND DIEBACK
Canker on Oleander stem, caused by
Botryospaeria obtusa spores are
produced in black, pimple-like structures
in the bark.
OAK WILT
 Caused by a fungus
 Affects: live oak, shumard oak,
spanish oak, and blackjack oak
 Spread by sap-feeding beetles, root
grafts
 Prevention: prune during periods of
low insect activity, removal of
infected trees and soil trenching
to prevent root grafts
OAK WILT
Some
trees
will not
die, but
are
stunted
forever.
OAK WILT
CHARACTERISTIC LEAF SYMPTOM ON LIVE OAK
OAK WILT
NOTE: This tree’s infection was caused by stress from too
much soil added…Where are the root flares?
Injectors
that
supply
fungicides
will do
little, but
cost a lot.
SLIME FLUX (WETWOOD)
This is a water soaking of
heartwood affecting many tree
species & is associated with
various bacterial species.
Liquid will drain from
openings of trunks, often
staining the outside. it is
associated with branch
dieback, but its role in tree
mortality is not certain. there
is no treatment or prevention
for this condition.
FIRE BLIGHT
 Caused by a bacterium
 Affects plants in the rose family: in
Texas, particularly apple, pear & photinia
 Bacterium can be spread by pollinating
insects at bloom time
 Confirm diagnosis since may mimic
herbicide damage
 Prune affected branches at least 8”
below symptoms
FIREBLIGHT
• left: branch
dieback
• right: quick
death of
leaves, often
associated
with flowers
(source of
infection)
FOOT ROT OF CITRUS
 Caused by a fungus, Phytophthora
(several species)
 Infection through wounds of trunk,
leading to defoliation and fruit drop
 Soilborne, other plants susceptible,
depending upon the fungus species
involved
 Treated with fungicides
FOOT ROT OF CITRUS
FOOT ROT OF CITRUS
DETAIL OF SYMPTOMS
ON LOWER TRUNK
PHYTOPHTHORA ROOT ROT AND
LEAF BLIGHT OF HIBISCUS
Too much
soil
moisture
and/or
poor
drainage
PHYTOPHTHORA ROOT ROT AND
LEAF BLIGHT OF HIBISCUS
PYTHIUM ROOT ROT OF HIBISCUS
EXTENSIVE ROOT ROT LEADS TO WILTING
AND DEATH. CONTROL WITH SANITATION,
GOOD DRAINAGE AND FUNGICIDES.
OLEANDER LEAF SCORCH
 Caused by a bacterium, Xylella fastidiosa: a




pathovar (strain) specific to oleander
Started showing up in late 1990’s
Bacterium can be spread by some
leafhoppers & sharpshooters
Confirm diagnosis at p.d. clinic
No treatment, but some cultivars may have
resistance
OLEANDER LEAF SCORCH
Landscapers’ nightmare!
OLEANDER LEAF SCORCH
PHOENIX LETHAL DECLINE
 Cause: a phytoplasma (ultra-small, wall-less




type of bacterium)
Some strains spread by leafhoppers &
planthoppers
Confirm diagnosis at p.d. clinic
Phoenix spp. susceptible, Sabal and
Washingtonia palms resistant
recent outbreak (2001) in Corpus Christi
PHOENIX LETHAL DECLINE
PHOENIX LETHAL DECLINE
RACHIS BLIGHT OF PALMS
NON-INFECTIOUS (NONLIVING) CAUSES OF TREE
AND SHRUB DEATH
FREEZE DAMAGE
LIGHTNING DAMAGE
• If lightening
makes a
spiral the
trees is
DEAD.
• If the strike
is mostly
straight up
and down,
then there is
a chance
DROUGHT & SALT STRESS
Right: typical symptoms.
Left: salt residue on soil surface
SOIL-APPLIED HERBICIDE
Herbicide (Krovar) was applied to citrus orchard
soil. Live oak roots grew into
orchard soil and picked up the herbicide.
SOIL-APPLIED HERBICIDE
variations in foliar damage
from krovar
SOIL STERILANT
INFECTIOUS DISEASES
(FUNGI AND OTHER
ORGANISMS) THAT
DISFIGURE OR BLEMISH
SHOOTS AND LEAVES,
BUT DO NO CAUSE
DIEBACK
CROWN GALL



Cause: bacterium
wide host range
spread by pruning
tools and splashing
water
 galls formed at base
of shoot
OLEANDER OLIVE KNOT
Caused by a bacterium with a
narrow host range.
GALL RUST FUNGI
Gall Rust on Acacia
GALL RUST FUNGI
GYMNOSPORANGIUM SPECIES - infect
members of the cypress and rose families.
infection of both types of plants are required
to complete the life cycle of the fungus and
different spores infect each type.
FUNGI INFECTING FOLIAGE
TOP LEFT: Entomosporium on
photinia.
TOP RIGHT: Rust on live oak
BOTTOM LEFT: Lembosina
quercina on live oak
CERCOSPORA LEAF BLIGHT OF
PITTOSPORUM
ANTHRACNOSE FUNGI
Shows up
mostly in
summer.
Treat at
budbreak.
DOWNY MILDEW OF ROSE
Cool weather fungus
POWDERY MILDEW FUNGI
TOP: on wild olive
RIGHT: on live oak
VIRUS DISEASES
Ring Spot Virus on rose.
NON-INFECTIOUS (NONLIVING) CAUSES OF TREE
AND SHRUB
DISFIGUREMENT OR
BLEMISHES, BUT NOT
DEATH
HERBICIDE DRIFT
HERBICIDES (E.G. 2,4-D) can drift onto foliage,
causing growth
deformations
NUTRIENT DEFICIENCIES
IRON DEFICIENCY IN
TEXAS IS USUALLY
RELATED TO HIGH PH
SOILS
NUTRIENT DEFICIENCIES
Zinc Deficiency – less pronounced than iron def.
INSECTS AND PLANTS
THAT DISFIGURE OR
BLEMISH SHOOTS AND
LEAVES, BUT DO NO
CAUSE DIEBACK
INSECT GALLS
GALL MITE on live oak leaf.
INSECT GALL on bark of
Texas ebony.
INSECT DAMAGE (FOLIAGE)
TRUE MISTLETOE
Parasite –
popular during
Christmas,
better than
Love Potion #9.
DODDER
Parasite like mistletoe.
OTHER, LIVING CAUSES
OF TREE AND SHRUB
DISFIGUREMENT OR
BLEMISHES, BUT NOT
DEATH
FOLIAR DAMAGE
SOOTY MOLD FUNGUS
ON LIVE OAK. The
fungus is usually
associated with insect
honeydew.
LEAF SPOT ON MAGNOLIA
caused by algae.
LICHENS
BALL MOSS
FASCIATION
ON HIBISCUS
ON MOUNTAIN
LAUREL
FASCIATION is a flattening of the
stem, caused by a mutation in
the plant